View source for Solar System

{{Short description|The Sun and objects orbiting it}}
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{{Use dmy dates|date=August 2024}}
{{Use American English|date=August 2024}}
{{Infobox planetary system|background=#efefef
| title = Solar System
| image = {{Switcher|[[File:Solar System true color.jpg|upright=1.3|frameless]]|without captions|[[File:Solar System true color (title and caption).jpg|upright=1.3|frameless]]|with captions|default=1}}
| image_alt = A true-color image of the Solar System with sizes, but not distances, to scale. The order of the planets are from right to left.
| image_size = 400px
| caption = {{Longitem|The [[Sun]], [[Planets of the solar system|planets, moons and dwarf planets]]{{Efn|The [[Asteroid Belt]], [[Kuiper Belt]], and [[Scattered Disc]] are not added because the individual asteroids are too small to be shown on the diagram.}}<br />(true color, size to scale, distances not to scale)|style=padding:2px 0 4px 0;}}
| age = 4.568&nbsp;billion years{{refn|group=lower-alpha|name=AgeSolarSystem}}
| location = {{Longitem|{{unbulleted list
    |{{nowrap|[[Local Interstellar Cloud]]}}
    |[[Local Bubble]]<ref name="JPL interstellar">{{cite web |url=http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/neighborhood.html |title=Our Local Galactic Neighborhood | website=  interstellar.jpl.nasa.gov |publisher=NASA |series=Interstellar Probe Project |year= 2000 |access-date=8 August 2012 |archive-url=https://web.archive.org/web/20131121061128/http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/neighborhood.html |archive-date=21 November 2013 |url-status=dead }}</ref>
    |[[Orion–Cygnus Arm]]
    |[[Milky Way]]<ref>{{Cite web |last=Hurt |first=R. |date=8 November 2017 |title=The Milky Way Galaxy |url=https://science.nasa.gov/resource/the-milky-way-galaxy/ |access-date=19 April 2024 |website=science.nasa.gov |language=en-US}}</ref>}}}}
| neareststar = {{Longitem|{{Ublist
    |[[Proxima Centauri]]
    |&nbsp;(4.2465&nbsp;[[Light-year|ly]])<ref name="lurie2014" group="D">{{cite journal |last1=Lurie |first1=John C. |last2=Henry |first2=Todd J. |last3=Jao |first3=Wei-Chun |last4=Quinn |first4=Samuel N. |last5=Winters |first5= Jennifer G. |last6=Ianna |first6=Philip A. |last7=Koerner |first7=David W. |last8= Riedel |first8=Adric R. |last9=Subasavage |first9=John P. | display-authors = 3| year= 2014 |title=The Solar neighborhood. XXXIV. A search for planets orbiting nearby M dwarfs using astrometry |journal=The Astronomical Journal |volume=148 |issue= 5 |pages=91 |arxiv=1407.4820 |bibcode= 2014AJ....148...91L |doi= 10.1088/0004-6256/148/5/91 |s2cid= 118492541 |issn = 0004-6256}}</ref>
    |[[Alpha Centauri]]
    |&nbsp;(4.36&nbsp;ly)<ref name="RECONS" group="D">{{cite web|work= astro.gsu.edu| publisher= Research Consortium On Nearby Stars, Georgia State University|date=7 September 2007|title=The One Hundred Nearest Star Systems |url=http://www.astro.gsu.edu/RECONS/TOP100.posted.htm|access-date=2 December 2014|archive-url=https://web.archive.org/web/20071112173559/http://www.chara.gsu.edu/RECONS/TOP100.posted.htm|archive-date=12 November 2007| url-status=live}}</ref>}}}}

| frostline = {{val|5|u=AU|p=~}}<ref name="Mumma">{{Cite journal |last1=Mumma |first1=M. J. |last2=Disanti |first2=M. A. |last3=Dello Russo |first3=N. |last4=Magee-Sauer |first4=K. |last5=Gibb |first5=E. |last6=Novak |first6=R. |display-authors = 3| year= 2003 |title=Remote infrared observations of parent volatiles in comets: A window on the early solar system |journal=Advances in Space Research |volume=31 |issue=12 |pages=2563–2575 |bibcode= 2003AdSpR..31.2563M |citeseerx= 10.1.1.575.5091 |doi=10.1016/S0273-1177(03)00578-7}}</ref>
| outerplanetname = [[Neptune]]
| semimajoraxis = 30.07 AU<ref name=Horizons group="D">{{cite web |first=Donald K. |last=Yeomans |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%278%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%272000-01-01%27&STOP_TIME=%272000-01-02%27&STEP_SIZE=%27200%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27 |title=HORIZONS Web-Interface for Neptune Barycenter (Major Body=8) |publisher=[[JPL Horizons On-Line Ephemeris System]] | website= jpl.nasa.gov|access-date=18 July 2014 |archive-date=7 September 2021 |archive-url=https://web.archive.org/web/20210907055935/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%278%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%272000-01-01%27&STOP_TIME=%272000-01-02%27&STEP_SIZE=%27200%20years%27&CENTER=%27%400%27&OUT_UNITS=%27AU-D%27 |url-status=live }}—Select "Ephemeris Type: Orbital Elements", "Time Span: 2000-01-01 12:00 to 2000-01-02". ("Target Body: Neptune Barycenter" and "Center: Solar System Barycenter (@0)".)</ref>
| Kuiper_cliff = 50–70 AU<ref name="twotino">{{cite journal | first1= E. I.| last1= Chiang |title=Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances |journal=[[The Astronomical Journal]] |volume=126 |issue=1 |pages=430–443 |date=2003 |doi=10.1086/375207 |last2=Jordan |first2=A. B. |last3=Millis |first3=R. L. |last4=Buie |first4=M. W. |last5=Wasserman |first5=L. H. |last6=Elliot |first6=J. L. |last7=Kern |first7=S. D. |last8=Trilling |first8=D. E. |last9=Meech |first9=K. J. | display-authors = 3| bibcode= 2003AJ....126..430C |arxiv=astro-ph/0301458 |s2cid=54079935}}</ref><ref name= "KuiperGap">{{cite journal |first1=C. | last1=de la Fuente Marcos |first2=R. | last2= de la Fuente Marcos |title=Past the outer rim, into the unknown: structures beyond the Kuiper Cliff |journal=[[Monthly Notices of the Royal Astronomical Society Letters]] |volume=527 |issue=1 |pages= L110–L114 |url=https://academic.oup.com/mnrasl/article-abstract/527/1/L110/7280408 |publication-date=20 September 2023 |date=January 2024 |access-date=28 September 2023 |bibcode=2024MNRAS.527L.110D |arxiv=2309.03885 |doi=10.1093/mnrasl/slad132 | doi-access=free |s2cid= |archive-date=28 October 2023 |archive-url=https://web.archive.org/web/20231028132004/https://academic.oup.com/mnrasl/article-abstract/527/1/L110/7280408 |url-status=live}}</ref>
| heliopause = detected at 120 AU<ref name="heliopause">{{cite web|url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html#.UjJLPZKR86s|title=NASA Spacecraft Embarks on Historic Journey Into Interstellar Space|first=Tony|last=Greicius| website= nasa.gov| date=5 May 2015|access-date=19 April 2024|archive-date=11 June 2020|archive-url=https://web.archive.org/web/20200611233345/https://www.nasa.gov/mission_pages/voyager/voyager20130912.html#.UjJLPZKR86s|url-status=dead}}</ref>
| hillsphere = 1.1 pc (230,000 AU)<ref name="Chebotarev">{{cite journal |last1=Chebotarev |first1=G. A. |title=Gravitational Spheres of the Major Planets, Moon and Sun |journal=Astronomicheskii Zhurnal |date=1 January 1963 |volume=40 |pages=812 |bibcode=1964SvA.....7..618C |url=https://adsabs.harvard.edu/full/1964SvA.....7..618C |issn=0004-6299 |access-date=6 May 2024 |archive-date=7 May 2024 |archive-url=https://web.archive.org/web/20240507030847/https://adsabs.harvard.edu/full/1964SvA.....7..618C |url-status=live }}</ref> – 0.865 pc (178,419 AU)<ref>{{cite journal |last1=Souami |first1=D |last2= Cresson |first2=J |last3=Biernacki |first3=C |last4=Pierret |first4=F |title=On the local and global properties of gravitational spheres of influence |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=21 August 2020 |volume= 496 |issue=4 |pages= 4287–4297 |doi= 10.1093/mnras/staa1520|doi-access=free | arxiv= 2005.13059 }}</ref>

| noknown_stars = yes
| noknown_planets = yes
| stars = [[Sun]]
| planets = {{Longitem|{{Plainlist|*[[Mercury (planet)|Mercury]]
*[[Venus]]
*[[Earth]]
*[[Mars]]
*[[Jupiter]]
*[[Saturn]]
*[[Uranus]]
*[[Neptune]]}}}}
| dwarfplanets = {{Longitem|{{Plainlist|
*{{Dp|Ceres}}
*{{Dp|Orcus}}
*[[Pluto]]
*[[Haumea]]
*{{Dp|Quaoar}}
*[[Makemake]]
*{{Dp|Gonggong}}
*[[Eris (dwarf planet)|Eris]]
*{{Dp|Sedna}}
*&nbsp;[[List of possible dwarf planets|''more candidates...'']]
}}}}
| satellites = 758<ref name="JPLbodies" group="D">{{Cite web |title=Solar System Objects |url=https://ssd.jpl.nasa.gov |url-status=live |archive-url=https://web.archive.org/web/20210707142304/https://ssd.jpl.nasa.gov |archive-date=7 July 2021 |access-date=14 August 2023 |publisher=NASA/JPL Solar System Dynamics}}</ref>
| minorplanets = 1,368,528<ref name="MPCSummary" group="D">{{Cite web |title=Latest Published Data |url=https://minorplanetcenter.net/mpc/summary |access-date=27 May 2024 |website=The International Astronomical Union Minor Planet Center |archive-date=5 March 2019 |archive-url=https://web.archive.org/web/20190305034947/https://minorplanetcenter.net/mpc/summary |url-status=live }}</ref>
| comets = 4,591<ref name=MPCSummary group="D"/>

| inclination = ~60°, to the ecliptic{{Refn |group=lower-alpha |name=angle}}<!-- If anyone can find a cited value for the inclination of the Solar System's invariable plane to the galactic plane, please replace this value -->
| galacticcenter = {{longitem|24,000–28,000 ly}}<ref name="francis14">{{cite journal |first1=Charles |last1=Francis |first2=Erik |last2=Anderson |s2cid= 119235554 |title=Two estimates of the distance to the Galactic Centre |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=June 2014 |volume=441 |issue=2 |pages=1105–1114 |doi=10.1093/mnras/stu631 |doi-access=free |bibcode= 2014MNRAS.441.1105F |arxiv=1309.2629}}</ref>
| orbitalspeed = {{longitem|720,000&nbsp;km/h (450,000&nbsp;mi/h)<ref name="roughfactsofthesun" />}}
| orbitalperiod = ~230 [[million year]]s<ref name="roughfactsofthesun">{{Cite web |title=Sun: Facts |url=https://science.nasa.gov/sun/facts/ |access-date=19 April 2024 |website=science.nasa.gov |language=en-US |archive-date=19 April 2024 |archive-url=https://web.archive.org/web/20240419151126/https://science.nasa.gov/sun/facts/ |url-status=live }}</ref>
| spectral = [[G-type main-sequence star|G2V]]
}}

The '''Solar System'''<ref group="lower-alpha">[[Capitalization]] of the name varies. The [[International Astronomical Union]], the authoritative body regarding [[astronomical nomenclature]], specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar System" and "solar system" structures in their [http://www.iau.org/public/themes/naming/ naming guidelines document] {{Webarchive|url=https://web.archive.org/web/20210725053113/https://www.iau.org/public/themes/naming |date=25 July 2021 }}. The name is commonly rendered in lower case ('solar system'), as, for example, in the ''[[Oxford English Dictionary]]'' and [http://www.m-w.com/dictionary/solar%20system ''Merriam-Webster's 11th Collegiate Dictionary''] {{Webarchive|url=https://web.archive.org/web/20080127201148/http://www.m-w.com/dictionary/solar%20system |date=27 January 2008 }}.</ref> is the [[gravitationally bound]] system of the [[Sun]] and the objects that [[orbit]] it.<ref name="IAU Office of Astronomy for Education y607">{{cite web | title=IAU Office of Astronomy for Education | website=astro4edu.org | publisher=IAU Office of Astronomy for Education | url=https://astro4edu.org/resources/glossary/term/314/ | access-date=11 December 2023 | archive-date=11 December 2023 | archive-url=https://web.archive.org/web/20231211093539/https://astro4edu.org/resources/glossary/term/314/ | url-status=live }}</ref> It [[Formation and evolution of the Solar System|formed about 4.6&nbsp;billion years ago]] when a dense region of a [[molecular cloud]] collapsed, forming the Sun and a [[protoplanetary disc]]. The Sun is a typical star that maintains a [[hydrostatic equilibrium|balanced equilibrium]] by the [[thermonuclear fusion|fusion]] of hydrogen into helium at its [[stellar core|core]], releasing this energy from its outer [[photosphere]]. Astronomers [[stellar classification|classify]] it as a [[G-type main-sequence star]].

The largest objects that orbit the Sun are the eight [[planet]]s. In order from the Sun, they are four [[terrestrial planet]]s ([[Mercury (planet)|Mercury]], [[Venus]], [[Earth]] and [[Mars]]); two [[gas giant]]s ([[Jupiter]] and [[Saturn]]); and two [[ice giant]]s ([[Uranus]] and [[Neptune]]). All terrestrial planets have solid surfaces. Inversely, all [[giant planets]] do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn.

There is a strong consensus among astronomers{{Efn|The [[International Astronomical Union]]'s Minor Planet Center has yet to officially list Orcus, Quaoar, Gonggong, and Sedna as dwarf planets as of 2024.}} that the Solar System has at least nine [[dwarf planet]]s: {{Dp|Ceres}}, {{Dp|Orcus}}, [[Pluto]], {{Dp|Haumea}}, {{Dp|Quaoar}}, {{Dp|Makemake}}, {{Dp|Gonggong}}, {{Dp|Eris}}, and {{Dp|Sedna}}. There are a vast number of [[Small Solar System body|small Solar System bodies]], such as [[asteroid]]s, [[comet]]s, [[Centaur (minor planet)|centaurs]], [[meteoroid]]s, and [[interplanetary dust cloud]]s. Some of these bodies are in the [[asteroid belt]] (between Mars's and Jupiter's orbit) and the [[Kuiper belt]] (just outside Neptune's orbit).{{efn|For more classifications of Solar System objects, see [[List of minor-planet groups]] and {{Section link|Comet|Classification}}.}} Six planets, seven dwarf planets, and other bodies have orbiting [[natural satellite]]s, which are commonly called 'moons'.

The Solar System is constantly flooded by the Sun's [[charged particle]]s, the [[solar wind]], forming the [[heliosphere]]. Around 75–90 [[astronomical unit]]s from the Sun,{{Efn|The scale of the Solar System is sufficiently large that astronomers use a custom unit to express distances. The [[astronomical unit]], abbreviated AU, is equal to {{Convert|1|AU|km mi|lk=off|disp=out|abbr=~}}. This is what the distance from the Earth to the Sun would be if the planet's orbit were perfectly circular.<ref>{{Cite journal |last=Standish |first=E. M. |date=April 2005 |title=The Astronomical Unit now |journal=Proceedings of the International Astronomical Union |volume=2004 |issue=IAUC196 |pages=163–179 |bibcode=2005tvnv.conf..163S |doi=10.1017/S1743921305001365 |s2cid=55944238 |doi-access=free}}</ref>}} the solar wind is halted, resulting in the [[Heliopause (astronomy)|heliopause]]. This is the boundary of the Solar System to [[interstellar space]]. The outermost region of the Solar System is the theorized [[Oort cloud]], the source for [[long-period comet]]s, extending to a radius of {{val|2000|–|200000|u=AU|fmt=commas}}. The closest star to the Solar System, [[Proxima Centauri]], is {{convert|4.25|ly|AU}} away. Both stars belong to the [[Milky Way]] galaxy.

== Formation and evolution ==
{{Main|Formation and evolution of the Solar System}}

=== Past ===
[[File:Soot-line1.jpg|thumb|upright=1.35|Diagram of the early Solar System's [[protoplanetary disk]], out of which Earth and other Solar System bodies formed]]
The Solar System formed at least 4.568&nbsp;billion years ago from the gravitational collapse of a region within a large [[molecular cloud]].{{Refn|name=AgeSolarSystem|group=lower-alpha|The date is based on the oldest [[inclusion (mineral)|inclusions]] found to date in [[meteorite]]s, {{Val|4568.2|+0.2|-0.4}} million years, and is thought to be the date of the formation of the first solid material in the collapsing nebula.<ref>{{Cite journal |last1=Bouvier |first1=A. |last2=Wadhwa |first2=M. |author-link2=Meenakshi Wadhwa |year=2010 |title=The age of the Solar System redefined by the oldest Pb–Pb age of a meteoritic inclusion |journal=Nature Geoscience |volume=3 |issue=9 |pages= 637–641 |bibcode=2010NatGe...3..637B |doi=10.1038/NGEO941 |s2cid=56092512}}</ref>}} This initial cloud was likely several light-years across and probably birthed several stars.<ref name="Arizona">{{Cite web |last=Zabludoff |first=Ann |title= Lecture 13: The Nebular Theory of the origin of the Solar System |url=http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html |url-status=live |archive-url=https://archive.today/20120710135114/http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html |archive-date=10 July 2012 |access-date=27 December 2006 |website=NATS 102: The Physical Universe |publisher=University of Arizona}}</ref> As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements [[Nuclear fusion|fused]] by previous generations of stars.<ref name=":3" />

As the [[solar nebula|pre-solar nebula]]<ref name=":3">{{Cite conference |last=Irvine |first=W. M. |date=1983 |title= The chemical composition of the pre-solar nebula |volume=1 |pages=3 |bibcode= 1983coex....1....3I |book-title=Cometary exploration; Proceedings of the International Conference}}</ref> collapsed, [[conservation of angular momentum]] caused it to rotate faster. The center, where most of the mass collected, became increasingly hotter than the surroundings.<ref name="Arizona" /> As the contracting nebula spun faster, it began to flatten into a [[protoplanetary disc]] with a diameter of roughly {{val|200|u=AU}}<ref name="Arizona" /><ref>{{cite journal | title=Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective | last=Vorobyov | first=Eduard I. | journal=The Astrophysical Journal | volume=729 | issue=2 | at=id. 146 | date=March 2011 | doi=10.1088/0004-637X/729/2/146 | arxiv=1101.3090 | bibcode=2011ApJ...729..146V | quote=estimates of disk radii in the Taurus and Ophiuchus star forming regions lie in a wide range between 50 AU and 1000 AU, with a median value of 200 AU.}}</ref> and a hot, dense [[protostar]] at the center.<ref>{{Cite journal |last=Greaves |first=Jane S. |date=7 January 2005 |title=Disks Around Stars and the Growth of Planetary Systems |journal=[[Science (journal)|Science]] |volume=307 |issue=5706 |pages=68–71 |bibcode=2005Sci...307...68G |doi=10.1126/science.1101979 |pmid=15637266 |s2cid=27720602}}</ref><ref>{{Cite book |publisher= Space Studies Board, Committee on Planetary and Lunar Exploration, National Research Council, Division on Engineering and Physical Sciences, National Academies Press |title=Strategy for the Detection and Study of Other Planetary Systems and Extrasolar Planetary Materials: 1990–2000 |date=1990 |isbn=978-0309041935 |publication-place=Washington D.C. |pages=21–33 |chapter=3. Present Understanding of the Origin of Planetary Systems |access-date=9 April 2022 |chapter-url=https://books.google.com/books?id=y56pS7SJs_8C&pg=PT29 |archive-url=https://web.archive.org/web/20220409211803/https://books.google.com/books?id=y56pS7SJs_8C&pg=PT29&lpg=PT29 |archive-date=9 April 2022 |url-status=live}}</ref> The planets formed by [[accretion (astrophysics)|accretion]] from this disc,<ref>{{Cite journal |last1=Boss |first1=A. P. |last2=Durisen |first2=R. H. |date=2005 |title=Chondrule-forming Shock Fronts in the Solar Nebula: A Possible Unified Scenario for Planet and Chondrite Formation |journal=[[The Astrophysical Journal]] |volume=621 |issue=2 |page=L137 |arxiv=astro-ph/0501592 |bibcode=2005ApJ...621L.137B |doi=10.1086/429160 |s2cid=15244154}}</ref> in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies. Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover [[small Solar System body|minor bodies]].<ref name="bennett_8.2" /><ref>{{Cite book |last1=Nagasawa |first1=M. |title=Protostars and Planets V |last2=Thommes |first2=E. W. |last3=Kenyon |first3=S. J. |last4=Bromley |first4=B. C. |last5=Lin |first5=D. N. C. |date=2007 | display-authors = 3 |publisher=University of Arizona Press |editor-last=Reipurth |editor-first=B. |publication-place=Tucson |pages=639–654 |chapter=The Diverse Origins of Terrestrial-Planet Systems |bibcode= 2007prpl.conf..639N |access-date=10 April 2022 |editor-last2=Jewitt |editor-first2=D. |editor-last3=Keil |editor-first3=K. |chapter-url=https://jila.colorado.edu/~pja/astr5820/nagasawa.pdf |archive-url=https://web.archive.org/web/20220412010025/https://jila.colorado.edu/~pja/astr5820/nagasawa.pdf |archive-date=12 April 2022 |url-status=live}}</ref>

Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the [[Frost line (astrophysics)|frost line]]). They eventually formed the rocky planets of Mercury, Venus, Earth, and Mars. Because these [[Refractory (planetary science)|refractory]] materials only comprised a small fraction of the solar nebula, the terrestrial planets could not grow very large.<ref name="bennett_8.2" />

The giant planets (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where material is cool enough for [[Volatile (astrogeology)|volatile]] icy compounds to remain solid. The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium, the lightest and most abundant elements.<ref name="bennett_8.2" /> Leftover debris that never became planets congregated in regions such as the asteroid belt, Kuiper belt, and Oort cloud.<ref name="bennett_8.2">{{Cite book |last=Bennett |first=Jeffrey O. |title=The cosmic perspective |date=2020 |publisher=Pearson |isbn= 978-0-134-87436-4 |edition=9th |location=Hoboken, New Jersey |chapter= Chapter 8.2}}</ref>

Within 50&nbsp;million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin [[nuclear fusion|thermonuclear fusion]].<ref name="Yi2001">{{Cite journal |last1=Yi |first1=Sukyoung |last2=Demarque |first2=Pierre |last3=Kim |first3=Yong-Cheol |last4=Lee |first4=Young-Wook |last5=Ree |first5=Chang H. |last6=Lejeune |first6=Thibault |last7=Barnes |first7= Sydney | display-authors = 3| date=2001 |title=Toward Better Age Estimates for Stellar Populations: The ''Y''<sup>2</sup> Isochrones for Solar Mixture |journal= [[Astrophysical Journal Supplement]] |volume=136 |issue=2 |pages=417–437 |arxiv=astro-ph/0104292 |bibcode= 2001ApJS..136..417Y |doi=10.1086/321795 |s2cid=118940644}}</ref> As helium accumulates at its core, the Sun is growing brighter;<ref name=":4">{{Cite journal |last=Gough |first=D. O. |date=November 1981 |title=Solar Interior Structure and Luminosity Variations |journal=Solar Physics |volume=74 |issue=1 |pages=21–34 |bibcode=1981SoPh...74...21G |doi= 10.1007/BF00151270 |s2cid=120541081}}</ref> early in its main-sequence life its brightness was 70% that of what it is today.<ref>{{Cite journal |last=Shaviv |first=Nir J. |date=2003 |title=Towards a Solution to the Early Faint Sun Paradox: A Lower Cosmic Ray Flux from a Stronger Solar Wind |journal= [[Journal of Geophysical Research]] |volume=108 |issue=A12 |page=1437 |arxiv=astroph/0306477 |bibcode= 2003JGRA..108.1437S |doi= 10.1029/2003JA009997 |s2cid= 11148141}}</ref> The temperature, [[Nuclear reaction rate|reaction rate]], pressure, and density increased until [[hydrostatic equilibrium]] was achieved: the thermal pressure counterbalancing the force of gravity. At this point, the Sun became a [[main sequence|main-sequence]] star.<ref>{{Cite journal |last1= Chrysostomou |first1=A. |last2=Lucas |first2=P. W. |date=2005 |title=The Formation of Stars |journal= [[Contemporary Physics]] |volume=46 |issue=1 |pages=29–40 |bibcode= 2005ConPh..46...29C |doi= 10.1080/0010751042000275277 |s2cid= 120275197}}</ref> Solar wind from the Sun created the [[heliosphere]] and swept away the remaining gas and dust from the protoplanetary disc into interstellar space.<ref name=":4" />

Following the dissipation of the [[protoplanetary disk]], the [[Nice model]] proposes that [[Gravity assist|gravitational encounters]] between planetisimals and the gas giants caused each to [[Planetary migration|migrate]] into different orbits. This led to dynamical instability of the entire system, which scattered the planetisimals and ultimately placed the gas giants in their current positions. During this period, the [[grand tack hypothesis]] suggests that a final inward migration of Jupiter dispersed much of the asteroid belt, leading to the [[Late Heavy Bombardment]] of the inner planets.<ref>{{cite journal | title=Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets | last1=Gomes | first1=R. | last2=Levison | first2=H. F. | last3=Tsiganis | first3=K. | last4=Morbidelli | first4=A. | journal=Nature | year=2005 | volume=435 | pages=466–469 | doi=10.1038/nature03676 | pmid=15917802 | issue=7041 | bibcode=2005Natur.435..466G | doi-access=free }}</ref><ref>{{cite book | last=Crida | first=A. | chapter=Solar System Formation | date=2009 | title=Reviews in Modern Astronomy: Formation and Evolution of Cosmic Structures | volume=21 | pages=215–227 | arxiv=0903.3008 | bibcode= 2009RvMA...21..215C | doi=10.1002/9783527629190.ch12 | isbn=9783527629190 | s2cid=118414100 }}</ref>

=== Present and future ===
The Solar System remains in a relatively stable, slowly evolving state by following isolated, [[gravitationally bound]] orbits around the Sun.<ref>{{Cite journal |last1=Malhotra |first1=R. |last2=Holman |first2=Matthew |last3=Ito |first3=Takashi |date=October 2001 |title=Chaos and stability of the solar system |journal= Proceedings of the National Academy of Sciences |volume=98 |issue=22 |pages=12342–12343 |bibcode= 2001PNAS...9812342M |doi=10.1073/pnas.231384098 |pmc=60054 |pmid=11606772 |doi-access=free}}</ref> Although the Solar System has been fairly stable for billions of years, it is technically [[chaotic system|chaotic]], and may [[stability of the Solar System|eventually be disrupted]]. There is a small chance that another star will pass through the Solar System in the next few billion years. Although this could destabilize the system and eventually lead millions of years later to expulsion of planets, collisions of planets, or planets hitting the Sun, it would most likely leave the Solar System much as it is today.<ref>{{cite journal |first1=Sean |last1=Raymond |display-authors=etal |date=27 November 2023 |title=Future trajectories of the Solar System: dynamical simulations of stellar encounters within 100 au |url=https://academic.oup.com/mnras/article/527/3/6126/7452883?login=false |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=527 |issue=3 |pages=6126–6138 |arxiv=2311.12171 |bibcode=2024MNRAS.527.6126R |doi=10.1093/mnras/stad3604 |doi-access=free |access-date=10 December 2023 |archive-date=10 December 2023 |archive-url=https://web.archive.org/web/20231210152219/https://academic.oup.com/mnras/article/527/3/6126/7452883?login=false |url-status=live }}</ref>

[[File:Sun red giant.svg|thumb|The current Sun compared to its peak size in the red-giant phase]]
The Sun's main-sequence phase, from beginning to end, will last about 10&nbsp;billion years for the Sun compared to around two billion years for all other subsequent phases of the Sun's pre-[[stellar remnant|remnant]] life combined.<ref name= "mnras386_1">{{Cite journal |last1= Schröder |first1=K.-P. |last2=Connon Smith |first2=Robert |date=May 2008 |title= Distant future of the Sun and Earth revisited |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=386 |issue=1 |pages=155–163 |arxiv=0801.4031 |bibcode=2008MNRAS.386..155S |doi=10.1111/j.1365-2966.2008.13022.x |doi-access=free |s2cid=10073988}}</ref> The Solar System will remain roughly as it is known today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5&nbsp;billion years from now. This will mark the end of the Sun's main-sequence life. At that time, the core of the Sun will contract with hydrogen fusion occurring along a shell surrounding the inert helium, and the energy output will be greater than at present. The outer layers of the Sun will expand to roughly 260 times its current diameter, and the Sun will become a [[red giant]]. Because of its increased surface area, the surface of the Sun will be cooler ({{Convert|2,600|K|F}} at its coolest) than it is on the main sequence.<ref name="mnras386_1" />

The expanding Sun is expected to vaporize Mercury as well as Venus, and render Earth and Mars uninhabitable (possibly destroying Earth as well).<ref>{{cite web | url=https://science.nasa.gov/universe/exoplanets/giant-red-stars-may-heat-frozen-worlds-into-habitable-planets/ | title=Giant red stars may heat frozen worlds into habitable planets - NASA Science }}</ref><ref>{{cite journal |last1= Aungwerojwit |first1=Amornrat |last2= Gänsicke |first2=Boris T |last3=Dhillon |first3=Vikram S |last4=Drake |first4= Andrew |last5=Inight |first5=Keith |last6= Kaye |first6=Thomas G |last7=Marsh |first7=T R |last8=Mullen |first8=Ed |last9= Pelisoli |first9=Ingrid |last10=Swan |first10=Andrew | display-authors = 3 |title=Long-term variability in debris transiting white dwarfs |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=2024 |volume=530 |issue=1 |pages=117–128 |doi=10.1093/mnras/stae750 |doi-access=free|arxiv=2404.04422 }}</ref> Eventually, the core will be hot enough for helium fusion; the Sun will burn helium for a fraction of the time it burned hydrogen in the core. The Sun is not massive enough to commence the fusion of heavier elements, and nuclear reactions in the core will dwindle. Its outer layers will be ejected into space, leaving behind a dense [[white dwarf]], half the original mass of the Sun but only the size of Earth.<ref name="mnras386_1"/> The ejected outer layers may form a [[planetary nebula]], returning some of the material that formed the Sun—but now enriched with [[metallicity|heavier elements]] like carbon—to the [[interstellar medium]].<ref>{{Cite web|title=Planetary Nebulas|url=https://www.cfa.harvard.edu/research/topic/planetary-nebulas|access-date=6 April 2024|publisher=Harvard & Smithsonian Center for Astrophysics|website=cfa.harvard.edu|archive-date=6 April 2024|archive-url=https://web.archive.org/web/20240406205913/https://www.cfa.harvard.edu/research/topic/planetary-nebulas|url-status=live}}</ref><ref>{{Cite journal|url=https://www.nature.com/articles/s41550-018-0453-9.epdf?sharing_token=XozRTVzMDBR74HQBj2lbV9RgN0jAjWel9jnR3ZoTv0OzwWt8mLOdVW4Y_YiE39Le3Xp-8zVx5tUnLpAORu5j1mnJNZpxp_fWsbZgn60hEE3IHsu89UrtgD6uRRVi7jD74SBwEYsmB2RyB2RCfRqLbLr5EqTy1-rK2KrrLO-TxuHwLmapWXxYkuOn5Rgut4w4JuE1XKNeJeRNDNx_0juT0bPlXn9WB29_BzKx1pGlzEXtR677aZ3SUe5um8epWM4PgYT-VDXR6Jevm-M9SDszF4a2eWOeV0CdynDONJuE1n37sanK9itS1edHH_xrybrldJgWdACO4sxHnFn3DHdB0Q==|title=The mysterious age invariance of the planetary nebula luminosity function bright cut-off|first1=K.|last1=Gesicki|first2=A. A.|last2=Zijlstra|first3=M. M.|last3=Miller Bertolami|date=7 May 2018|journal=Nature Astronomy|volume=2|issue=7|pages=580–584|doi=10.1038/s41550-018-0453-9|arxiv=1805.02643|bibcode=2018NatAs...2..580G|hdl=11336/82487|s2cid=256708667|access-date=16 January 2024|archive-date=16 January 2024|archive-url=https://web.archive.org/web/20240116173409/https://www.nature.com/articles/s41550-018-0453-9.epdf?sharing_token=XozRTVzMDBR74HQBj2lbV9RgN0jAjWel9jnR3ZoTv0OzwWt8mLOdVW4Y_YiE39Le3Xp-8zVx5tUnLpAORu5j1mnJNZpxp_fWsbZgn60hEE3IHsu89UrtgD6uRRVi7jD74SBwEYsmB2RyB2RCfRqLbLr5EqTy1-rK2KrrLO-TxuHwLmapWXxYkuOn5Rgut4w4JuE1XKNeJeRNDNx_0juT0bPlXn9WB29_BzKx1pGlzEXtR677aZ3SUe5um8epWM4PgYT-VDXR6Jevm-M9SDszF4a2eWOeV0CdynDONJuE1n37sanK9itS1edHH_xrybrldJgWdACO4sxHnFn3DHdB0Q==|url-status=live}}</ref>

==General characteristics==
Astronomers sometimes divide the Solar System structure into separate regions. The [[inner Solar System]] includes Mercury, Venus, Earth, Mars, and the bodies in the [[asteroid belt]]. The [[outer Solar System]] includes Jupiter, Saturn, Uranus, Neptune, and the bodies in the [[Kuiper belt]].<ref>{{Cite web |title=The Planets |url=https://science.nasa.gov/solar-system/planets/ |access-date=6 April 2024 |publisher=NASA}}</ref> Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of [[Trans-Neptunian object|the objects beyond Neptune]].<ref>{{Cite web |title=Kuiper Belt: Facts |url=https://science.nasa.gov/solar-system/kuiper-belt/facts/ |access-date=6 April 2024 |publisher=NASA |archive-date=12 March 2024 |archive-url=https://web.archive.org/web/20240312024528/https://science.nasa.gov/solar-system/kuiper-belt/facts/ |url-status=live }}</ref>

=== Composition ===
{{Further|List of Solar System objects|List of interstellar and circumstellar molecules}}

The principal component of the Solar System is the Sun, a [[G-type main-sequence star]] that contains 99.86% of the system's known mass and dominates it gravitationally.<ref>{{Cite journal |last=Woolfson |first=M. |date=2000 |title=The origin and evolution of the solar system |journal=[[Astronomy & Geophysics]] |volume=41 |issue=1 |pages=1.12–1.19 |bibcode=2000A&G....41a..12W |doi=10.1046/j.1468-4004.2000.00012.x |doi-access=free}}</ref> The Sun's four largest orbiting bodies, the giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. The remaining objects of the Solar System (including the four terrestrial planets, the dwarf planets, moons, [[asteroid]]s, and comets) together comprise less than 0.002% of the Solar System's total mass.{{Refn |The mass of the Solar System excluding the Sun, Jupiter and Saturn can be determined by adding together all the calculated masses for its largest objects and using rough calculations for the masses of the Oort cloud (estimated at roughly 3 Earth masses),<ref>{{Cite arXiv |eprint=astro-ph/0512256 |first=Alessandro |last=Morbidelli |title=Origin and dynamical evolution of comets and their reservoirs |date=2005}}</ref> the Kuiper belt (estimated at 0.1 Earth mass)<ref name="Delsanti-Beyond_The_Planets"/> and the asteroid belt (estimated to be 0.0005 Earth mass)<ref name="Krasinsky2002"/> for a total, rounded upwards, of ~37 Earth masses, or 8.1% of the mass in orbit around the Sun. With the combined masses of Uranus and Neptune (~31 Earth masses) subtracted, the remaining ~6 Earth masses of material comprise 1.3% of the total orbiting mass.|name=footnoteD|group=lower-alpha}}

The Sun is composed of roughly 98% hydrogen and helium,<ref>{{Cite web |title=The Sun's Vital Statistics |url=http://solar-center.stanford.edu/vitalstats.html |url-status=live |archive-url=https://www.webcitation.org/6BOkQXma3?url=http://solar-center.stanford.edu/vitalstats.html |archive-date=14 October 2012 |access-date=29 July 2008 |publisher=Stanford Solar Center |postscript=,}} citing {{Cite book
|last=Eddy
|first=J.
|title=A New Sun: The Solar Results From Skylab
|url=https://history.nasa.gov/SP-402/contents.htm
|publisher=[[NASA]]
|date=1979
|page=37
|id=NASA SP-402
|access-date=12 July 2017
|archive-date=30 July 2021
|archive-url=https://web.archive.org/web/20210730024856/https://history.nasa.gov/SP-402/contents.htm
|url-status=live
}}</ref> as are Jupiter and Saturn.<ref>{{Cite web |last=Williams |first=David R. |date=7 September 2006 |title=Saturn Fact Sheet |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html |url-status=dead |archive-url=https://web.archive.org/web/20110804224236/http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html |archive-date=4 August 2011 |access-date=31 July 2007 |publisher=NASA }}</ref><ref name="Williams-Jupiter" /> A composition gradient exists in the Solar System, created by heat and [[light pressure]] from the early Sun; those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points. Objects farther from the Sun are composed largely of materials with lower melting points.<ref>{{Cite book |last1=Weissman |first1=Paul Robert |url=https://archive.org/details/encyclopediaofso0000unse_u6d1/page/615 |title=Encyclopedia of the solar system |last2=Johnson |first2=Torrence V. |date=2007 |publisher=Academic Press |isbn=978-0-12-088589-3 |page=[https://archive.org/details/encyclopediaofso0000unse_u6d1/page/615 615]}}</ref> The boundary in the Solar System beyond which those volatile substances could coalesce is known as the [[Frost line (astrophysics)|frost line]], and it lies at roughly five times the Earth's distance from the Sun.<ref name="Mumma" />

=== Orbits ===

[[File:Solar system orrery inner planets.gif|thumb|Animations of the Solar System's [[inner planet]]s orbiting. Each frame represents 2 days of motion.]]
[[File:Solar system orrery outer planets.gif|thumb|Animations of the Solar System's [[outer planet]]s orbiting. This animation is 100 times faster than the inner planet animation.]]

The planets and other large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the [[ecliptic]]. Smaller icy objects such as comets frequently orbit at significantly greater angles to this plane.<ref name="Levison2003">{{Cite journal |last1=Levison |first1=H.F. |author-link=Harold F. Levison |last2=Morbidelli |first2=A. |date=27 November 2003 |title=The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration |journal=[[Nature (journal)|Nature]] |volume=426 |issue=6965 |pages=419–421 |bibcode=2003Natur.426..419L |doi=10.1038/nature02120 |pmid=14647375 |s2cid=4395099}}</ref><ref>{{Cite journal |last1=Levison |first1=Harold F. |last2=Duncan |first2=Martin J. |date=1997 |title=From the Kuiper Belt to Jupiter-Family Comets: The Spatial Distribution of Ecliptic Comets |journal=[[Icarus (journal)|Icarus]] |volume=127 |issue=1 |pages=13–32 |bibcode=1997Icar..127...13L |doi=10.1006/icar.1996.5637}}</ref> Most of the planets in the Solar System have secondary systems of their own, being orbited by natural satellites called moons. All of the largest natural satellites are in [[synchronous rotation]], with one face permanently turned toward their parent. The four giant planets have planetary rings, thin discs of tiny particles that orbit them in unison.<ref name="bennett_4.5">{{Cite book |last1=Bennett |first1=Jeffrey O. |title=The Cosmic Perspective |last2=Donahue |first2=Megan |last3=Schneider |first3=Nicholas |last4=Voit |first4=Mark |date=2020 |publisher=Pearson |isbn=978-0-134-87436-4 |edition=9th |location=Hoboken, NJ |chapter=4.5 Orbits, Tides, and the Acceleration of Gravity |oclc=1061866912 |author-link2=Megan Donahue}}</ref>

As a result of the [[Formation and evolution of the Solar System|formation of the Solar System]], planets and most other objects orbit the Sun in the same direction that the Sun is rotating. That is, counter-clockwise, as viewed from above Earth's north pole.<ref>{{Cite magazine |last=Grossman |first=Lisa |date=13 August 2009 |title=Planet found orbiting its star backwards for first time |url=https://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html |url-status=live |magazine=New Scientist |archive-url=https://web.archive.org/web/20121017083955/http://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html |archive-date=17 October 2012 |access-date=10 October 2009}}</ref> There are exceptions, such as [[Halley's Comet]].<ref>{{Cite web |last=Nakano |first=Syuichi |date=2001 |title=OAA computing section circular |url=http://www.oaa.gr.jp/~oaacs/nk/nk866.htm |url-status=live |archive-url=https://web.archive.org/web/20190921103057/http://www.oaa.gr.jp/~oaacs/nk/nk866.htm |archive-date=21 September 2019 |access-date=15 May 2007 |publisher=Oriental Astronomical Association}}</ref> Most of the larger moons orbit their planets in [[Retrograde and prograde motion|prograde]] direction, matching the direction of planetary rotation; Neptune's moon [[Triton (moon)|Triton]] is the largest to orbit in the opposite, retrograde manner.<ref>{{Cite journal |last1=Agnor |first1=Craig B. |last2=Hamilton |first2=Douglas P. |date=May 2006 |title=Neptune's capture of its moon Triton in a binary–planet gravitational encounter |url=https://www.nature.com/articles/nature04792 |url-status=live |journal=[[Nature (journal)|Nature]] |language=en |volume=441 |issue=7090 |pages=192–194 |bibcode=2006Natur.441..192A |doi=10.1038/nature04792 |issn=1476-4687 |pmid=16688170 |s2cid=4420518 |archive-url=https://web.archive.org/web/20220415081402/https://www.nature.com/articles/nature04792 |archive-date=15 April 2022 |access-date=28 March 2022}}</ref> Most larger objects rotate around their own axes in the prograde direction relative to their orbit, though the rotation of Venus is retrograde.<ref>{{Cite book |last=Gallant |first=Roy A. |url=https://www.worldcat.org/oclc/6533014 |title=National Geographic Picture Atlas of Our Universe |date=1980 |publisher=National Geographic Society |isbn=0-87044-356-9 |editor-last=Sedeen |editor-first=Margaret |location=Washington, D.C. |pages=82 |oclc=6533014 |access-date=28 March 2022 |archive-url=https://web.archive.org/web/20220420161217/https://www.worldcat.org/title/national-geographic-picture-atlas-of-our-universe/oclc/6533014 |archive-date=20 April 2022 |url-status=live}}</ref>

To a good first approximation, [[Kepler's laws of planetary motion]] describe the orbits of objects around the Sun.<ref name=":0">{{Cite book |last1=Frautschi |first1=Steven C. |title=The Mechanical Universe: Mechanics and Heat |title-link=The Mechanical Universe |last2=Olenick |first2=Richard P. |last3=Apostol |first3=Tom M. |last4=Goodstein |first4=David L. |date=2007 |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |edition=Advanced |location=Cambridge [Cambridgeshire] |oclc=227002144 |author-link=Steven Frautschi |author-link3=Tom M. Apostol |author-link4=David L. Goodstein}}</ref>{{Rp|pages=433–437}} These laws stipulate that each object travels along an [[ellipse]] with the Sun at one [[focus (geometry)|focus]], which causes the body's distance from the Sun to vary over the course of its year. A body's closest approach to the Sun is called its ''[[perihelion]]'', whereas its most distant point from the Sun is called its ''[[aphelion]]''.<ref name=":8">{{Cite book |last1=Feynman |first1=Richard P. |title=The Feynman Lectures on Physics, Volume 1 |title-link=The Feynman Lectures on Physics |last2=Leighton |first2=Robert B. |last3=Sands |first3=Matthew L. |date=1989 |publisher=Addison-Wesley Pub. Co |isbn=0-201-02010-6 |location=Reading, Mass. |oclc=531535 |author-link=Richard Feynman |author-link2=Robert B. Leighton |author-link3=Matthew Sands |orig-date=1965}}</ref>{{Rp|location=9-6}} With the exception of Mercury, the orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. Kepler's laws only account for the influence of the Sun's gravity upon an orbiting body, not the gravitational pulls of different bodies upon each other. On a human time scale, these perturbations can be accounted for using [[numerical model of the Solar System|numerical models]],<ref name=":8" />{{Rp|location=9-6}} but the planetary system can change chaotically over billions of years.<ref>{{Cite journal |last1=Lecar |first1=Myron |last2=Franklin |first2=Fred A. |last3=Holman |first3=Matthew J. |last4=Murray |first4=Norman J. |date=2001 |title=Chaos in the Solar System |journal=Annual Review of Astronomy and Astrophysics |volume=39 |issue=1 |pages=581–631 |arxiv=astro-ph/0111600 |bibcode=2001ARA&A..39..581L |doi=10.1146/annurev.astro.39.1.581 |s2cid=55949289}}</ref>

The [[angular momentum]] of the Solar System is a measure of the total amount of orbital and [[rotational momentum]] possessed by all its moving components.<ref>{{Cite book |last=Piccirillo |first=Lucio |url=https://books.google.com/books?id=W0jpDwAAQBAJ&pg=PA210 |title=Introduction to the Maths and Physics of the Solar System |date=2020 |publisher=CRC Press |isbn=978-0429682803 |page=210 |access-date=10 May 2022 |archive-url=https://web.archive.org/web/20220730084321/https://www.google.com/books/edition/Introduction_to_the_Maths_and_Physics_of/W0jpDwAAQBAJ?gbpv=1&pg=PA210 |archive-date=30 July 2022 |url-status=live}}</ref> Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum.<ref name="Marochnik1995">{{Cite conference |last1=Marochnik |first1=L. |last2=Mukhin |first2=L. |date=1995 |title=Is Solar System Evolution Cometary Dominated? |series=Astronomical Society of the Pacific Conference Series |volume=74 |page=83 |bibcode=1995ASPC...74...83M |isbn=0-937707-93-7 |book-title=Progress in the Search for Extraterrestrial Life |editor=Shostak, G.S.}}</ref><ref>{{Cite journal |last1=Bi |first1=S. L. |last2=Li |first2=T. D. |last3=Li |first3=L. H. |last4=Yang |first4=W. M. |year=2011 |title=Solar Models with Revised Abundance |journal=[[The Astrophysical Journal]] |volume=731 |issue=2 |pages=L42 |arxiv=1104.1032 |bibcode=2011ApJ...731L..42B |doi=10.1088/2041-8205/731/2/L42 |s2cid=118681206}}</ref> The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of their mass, orbit, and distance from the Sun, with a possibly significant contribution from comets.<ref name="Marochnik1995" />

=== Distances and scales ===
[[File:Solar System distance to scale.svg|center|thumb|upright=2.5|To-scale diagram of distance between planets, with the white bar showing orbital variations. The size of the planets is not to scale.]]

The radius of the Sun is {{Cvt|0.0047|AU|km mi|sigfig=1|abbr=unit}}.<ref name="arxiv1203_4898">{{Cite journal |last1=Emilio |first1=Marcelo |last2=Kuhn |first2=Jeff R. |last3=Bush |first3=Rock I. |last4=Scholl |first4=Isabelle F. |year=2012 |title=Measuring the Solar Radius from Space during the 2003 and 2006 Mercury Transits |journal=[[The Astrophysical Journal]] |volume=750 |issue=2 |page=135 |arxiv=1203.4898 |bibcode=2012ApJ...750..135E |doi=10.1088/0004-637X/750/2/135 |s2cid=119255559}}</ref> Thus, the Sun occupies 0.00001% (1 part in 10<sup>7</sup>) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1&nbsp;millionth (10<sup>−6</sup>) that of the Sun. Jupiter, the largest planet, is {{val|5.2|u=AU}} from the Sun and has a radius of {{Convert|71000|km|AU mi|abbr=on|sigfig=2}}, whereas the most distant planet, Neptune, is {{val|30|u=AU}} from the Sun.<ref name="Williams-Jupiter">{{Cite web |last=Williams |first=David R. |date=23 December 2021 |title=Jupiter Fact Sheet |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html |url-status=live |archive-url=https://web.archive.org/web/20180122180353/https://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html |archive-date=22 January 2018 |access-date=28 March 2022 |website=NASA Goddard Space Flight Center}}</ref><ref>{{Cite web |last=Williams |first=David R. |date=23 December 2021 |title=Neptune Fact Sheet |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html |url-status=live |archive-url=https://web.archive.org/web/20161119045252/http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html |archive-date=19 November 2016 |access-date=28 March 2022 |website=NASA Goddard Space Flight Center}}</ref>

With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and the orbit of the next nearest object to the Sun. For example, Venus is approximately 0.33&nbsp;AU farther out from the Sun than Mercury, whereas Saturn is 4.3&nbsp;AU out from Jupiter, and Neptune lies 10.5&nbsp;AU out from Uranus. Attempts have been made to determine a relationship between these orbital distances, like the [[Titius–Bode law]]<ref>{{Cite journal |last=Jaki |first=Stanley L. |date=1 July 1972 |title=The Early History of the Titius-Bode Law |url=https://aapt.scitation.org/doi/abs/10.1119/1.1986734 |url-status=live |journal=American Journal of Physics |volume=40 |issue=7 |pages=1014–1023 |bibcode=1972AmJPh..40.1014J |doi=10.1119/1.1986734 |issn=0002-9505 |archive-url=https://web.archive.org/web/20220420161227/https://aapt.scitation.org/doi/abs/10.1119/1.1986734 |archive-date=20 April 2022 |access-date=2 April 2022}}</ref> and [[Mysterium Cosmographicum|Johannes Kepler's model]] based on the [[Platonic solid]]s,<ref>{{Cite journal |last=Phillips |first=J. P. |date=1965 |title=Kepler's Echinus |journal=Isis |volume=56 |issue=2 |pages=196–200 |doi=10.1086/349957 |issn=0021-1753 |jstor=227915 |s2cid=145268784}}</ref> but ongoing discoveries have invalidated these hypotheses.<ref name="Boss">{{Cite magazine |last=Boss |first=Alan |date=October 2006 |title=Is it a coincidence that most of the planets fall within the Titius-Bode law's boundaries? |url=https://astronomy.com/magazine/ask-astro/2006/10/is-it-a-coincidence-that-most-of-the-planets-fall-within-the-titius-bode-laws-boundaries |url-status=live |magazine=Astronomy |volume=30 |issue=10 |page=70 |archive-url=https://web.archive.org/web/20220316135255/https://astronomy.com/magazine/ask-astro/2006/10/is-it-a-coincidence-that-most-of-the-planets-fall-within-the-titius-bode-laws-boundaries |archive-date=16 March 2022 |access-date=9 April 2022 |series=Ask Astro}}</ref>

Some [[Solar System model]]s attempt to convey the relative scales involved in the Solar System in human terms. Some are small in scale (and may be mechanical—called [[Orrery|orreries]])—whereas others extend across cities or regional areas.<ref>{{Cite web |last=Ottewell |first=Guy |date=1989 |title=The Thousand-Yard Model: or, Earth as a Peppercorn |url=http://www.noao.edu/education/peppercorn/pcmain.html |url-status=dead |archive-url=https://web.archive.org/web/20160710065429/http://www.noao.edu/education/peppercorn/pcmain.html |archive-date=10 July 2016 |access-date=10 May 2012 |website=NOAO Educational Outreach Office}}</ref> The largest such scale model, the [[Sweden Solar System]], uses the 110-meter (361-foot) [[Avicii Arena]] in [[Stockholm]] as its substitute Sun, and, following the scale, Jupiter is a 7.5-meter (25-foot) sphere at [[Stockholm Arlanda Airport]], 40&nbsp;km (25&nbsp;mi) away, whereas the farthest current object, [[90377 Sedna|Sedna]], is a 10&nbsp;cm (4&nbsp;in) sphere in [[Luleå]], 912&nbsp;km (567&nbsp;mi) away.<ref>{{Cite web |title=Tours of Model Solar Systems |url=http://internal.psychology.illinois.edu/~wbrewer/solarmodel.html |url-status=dead |archive-url=https://web.archive.org/web/20110412124455/http://internal.psychology.illinois.edu/~wbrewer/solarmodel.html |archive-date=12 April 2011 |access-date=10 May 2012 |publisher=University of Illinois}}</ref><ref name="Sedna">{{Cite web |title=Luleå är Sedna. I alla fall om vår sol motsvaras av Globen i Stockholm |url=http://www.kuriren.nu/arkiv/2005/11/17/Lokalt/1510647/Lule%C3%A5-%C3%A4r-Sedna.aspx |url-status=dead |archive-url=https://web.archive.org/web/20100715074955/http://www.kuriren.nu/arkiv/2005/11/17/Lokalt/1510647/Lule%C3%A5-%C3%A4r-Sedna.aspx |archive-date=15 July 2010 |access-date=10 May 2010 |publisher=Norrbotten Kuriren (in Swedish)}}</ref> At that scale, the distance to Proxima Centauri would be roughly 8 times further than the Moon is from Earth.

If the Sun–Neptune distance is scaled to {{Convert|100|m|ft|4=-1}}, then the Sun would be about {{Convert|3|cm|abbr=on}} in diameter (roughly two-thirds the diameter of a golf ball), the giant planets would be all smaller than about {{Convert|3|mm|abbr=on}}, and [[Earth's diameter]] along with that of the other terrestrial planets would be smaller than a [[flea]] ({{Convert|0.3|mm|abbr=on|disp=or}}) at this scale.<ref>See, for example, {{Cite web |last=Office of Space Science |date=9 July 2004 |title=Solar System Scale |url=http://www.nasa.gov/audience/foreducators/5-8/features/F_Solar_System_Scale.html |url-status=live |archive-url=https://web.archive.org/web/20160827184323/http://www.nasa.gov/audience/foreducators/5-8/features/F_Solar_System_Scale.html |archive-date=27 August 2016 |access-date=2 April 2013 |website=NASA Educator Features}}</ref>

=== Habitability ===
{{Main|Planetary habitability in the Solar System}}
{{Multiple image|perrow = 1|total_width = 350
 | direction         = vertical

 <!--image 1-->
 | image1            = PIA21424 - The TRAPPIST-1 Habitable Zone.jpg
 | alt1              =
 | caption1          = Comparison of the habitable zones of the Solar System and [[TRAPPIST-1]], an ultracool red dwarf star known to have seven terrestrial planets in stable orbits around the star.
 <!--image 2-->
 | image2            = Diagram of different habitable zone regions by Chester Harman.jpg
 | alt2              =
 | caption2          = Comparison of the [[habitable zone]]s for different stellar temperatures, with a sample of known exoplanets plus the Earth, Mars, and Venus. From top to bottom are an [[F-type main-sequence star]], a [[G-type main-sequence star|yellow dwarf]] (G-type main-sequence star), an [[orange dwarf]] (K-type main-sequence star), a typical [[red dwarf]], and an [[ultra-cool dwarf]].
}}
Besides solar energy, the primary characteristic of the Solar System enabling the presence of life is the heliosphere and planetary magnetic fields (for those planets that have them). These magnetic fields partially shield the Solar System from high-energy interstellar particles called [[cosmic ray]]s. The density of cosmic rays in the [[interstellar medium]] and the strength of the Sun's magnetic field change on very long timescales, so the level of cosmic-ray penetration in the Solar System varies, though by how much is unknown.<ref name="Langner_et_al_2005">{{Cite journal |last1=Langner |first1=U. W. |last2=Potgieter |first2=M. S. |date=2005 |title=Effects of the position of the solar wind termination shock and the heliopause on the heliospheric modulation of cosmic rays |journal=[[Advances in Space Research]] |volume=35 |issue=12 |pages=2084–2090 |bibcode=2005AdSpR..35.2084L |doi=10.1016/j.asr.2004.12.005}}</ref>

The [[Circumstellar habitable zone|zone of habitability]] of the Solar System is conventionally located in the inner Solar System, where planetary surface or atmospheric temperatures admit the possibility of [[liquid water]].<ref name="NASA-20150407">{{Cite web |last1=Dyches |first1=Preston |last2=Chou |first2=Felcia |date=7 April 2015 |title=The Solar System and Beyond is Awash in Water |url=http://www.nasa.gov/jpl/the-solar-system-and-beyond-is-awash-in-water |url-status=dead |archive-url=https://web.archive.org/web/20150410113514/http://www.nasa.gov/jpl/the-solar-system-and-beyond-is-awash-in-water/ |archive-date=10 April 2015 |access-date=8 April 2015 |website=[[NASA]]}}</ref> Habitability might be possible in [[subsurface ocean]]s of various outer Solar System moons.<ref>{{Cite book |last1=Robert T. Pappalardo |url=https://books.google.com/books?id=Jpcz2UoXejgC |title=Europa |last2=William B. McKinnon |last3=K. Khurana |publisher=University of Arizona Press |year=2009 |isbn=978-0-8165-2844-8 |page=658 |access-date=6 April 2023 |archive-date=6 April 2023 |archive-url=https://web.archive.org/web/20230406102731/https://books.google.com/books?id=Jpcz2UoXejgC |url-status=live }} [https://books.google.com/books?id=Jpcz2UoXejgC&pg=PA658 Extract of page 658] {{Webarchive|url=https://web.archive.org/web/20230415082720/https://books.google.com/books?id=Jpcz2UoXejgC&pg=PA658 |date=15 April 2023 }}</ref>

=== Comparison with extrasolar systems ===
Compared to many extrasolar systems, the Solar System stands out in lacking planets interior to the orbit of Mercury.<ref name="Martin082015">{{Cite journal |last1=Martin |first1=Rebecca G. |last2=Livio |first2=Mario |year=2015 |title=The Solar System as an Exoplanetary System |journal=[[The Astrophysical Journal]] |volume=810 |issue=2 |page=105 |arxiv=1508.00931 |bibcode=2015ApJ...810..105M |doi=10.1088/0004-637X/810/2/105 |s2cid=119119390}}</ref><ref>{{Cite journal |last=Kohler |first=Susanna |date=25 September 2015 |title=How Normal is Our Solar System? |url=https://aasnova.org/2015/09/25/how-normal-is-our-solar-system |url-status=live |journal=Aas Nova Highlights |publisher=American Astronomical Society |page=313 |bibcode=2015nova.pres..313K |archive-url=https://web.archive.org/web/20220407043952/https://aasnova.org/2015/09/25/how-normal-is-our-solar-system |archive-date=7 April 2022 |access-date=31 March 2022}}</ref> The known Solar System lacks [[super-Earth]]s, planets between one and ten times as massive as the Earth,<ref name="Martin082015" /> although the hypothetical [[Planet Nine]], if it does exist, could be a super-Earth orbiting in the edge of the Solar System.<ref>{{Cite journal |last1=Sheppard |first1=Scott S. |author-link=Scott S. Sheppard |last2=Trujillo |first2=Chadwick |author-link2=Chad Trujillo |date=7 December 2016 |title=New extreme trans-Neptunian objects: Toward a super-Earth in the outer solar system |journal=The Astronomical Journal |volume=152 |issue=6 |page=221 |arxiv=1608.08772 |bibcode=2016AJ....152..221S |doi=10.3847/1538-3881/152/6/221 |issn=1538-3881 |s2cid=119187392 |doi-access=free}}</ref>

Uncommonly, it has only small terrestrial and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there is no "gap" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). As many of these super-Earths are closer to their respective stars than Mercury is to the Sun, a hypothesis has arisen that all planetary systems start with many close-in planets, and that typically a sequence of their collisions causes consolidation of mass into few larger planets, but in case of the Solar System the collisions caused their destruction and ejection.<ref name="Martin082015" /><ref>{{Cite journal |last1=Volk |first1=Kathryn |last2=Gladman |first2=Brett |year=2015 |title=Consolidating and Crushing Exoplanets: Did it happen here? |journal=[[The Astrophysical Journal Letters]] |volume=806 |page=L26 |arxiv=1502.06558 |bibcode=2015ApJ...806L..26V |doi=10.1088/2041-8205/806/2/L26 |s2cid=118052299 |number=2}}</ref>

The orbits of Solar System planets are nearly circular. Compared to many other systems, they have smaller [[orbital eccentricity]].<ref name="Martin082015" /> Although there are attempts to explain it partly with a bias in the [[Doppler spectroscopy|radial-velocity detection method]] and partly with long interactions of a quite high number of planets, the exact causes remain undetermined.<ref name="Martin082015" /><ref>{{Cite journal |last1=Goldreich |first1=Peter |last2=Lithwick |first2=Yoram |last3=Sari |first3=Re'em |year=2004 |title=Final Stages of Planet Formation |journal=[[The Astrophysical Journal]] |volume=614 |issue=1 |pages=497–507 |arxiv=astro-ph/0404240 |bibcode=2004ApJ...614..497G |doi=10.1086/423612 |s2cid=16419857}}</ref>

== Sun ==
{{Main|Sun}}
[[File:The Sun in white light.jpg|thumb|alt=White ball of plasma|The Sun in true white color]]

The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 [[Earth mass]]es),<ref>{{Cite web |title=Sun: Facts & Figures |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |url-status=dead |archive-url=https://web.archive.org/web/20080102034758/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |archive-date=2 January 2008 |access-date=14 May 2009 |publisher=NASA}}</ref> which comprises 99.86% of all the mass in the Solar System,<ref name="Woolfson00">{{Cite journal |last=Woolfson |first=M. |date=2000 |title=The origin and evolution of the solar system |journal=[[Astronomy & Geophysics]] |volume=41 |issue=1 |page=12 |bibcode=2000A&G....41a..12W |doi=10.1046/j.1468-4004.2000.00012.x |doi-access=free}}</ref> produces temperatures and densities in its [[solar core|core]] high enough to sustain nuclear fusion of hydrogen into helium.<ref>{{Cite book |last=Zirker |first=Jack B. |url=https://archive.org/details/journeyfromcente0000zirk |title=Journey from the Center of the Sun |date=2002 |publisher=[[Princeton University Press]] |isbn=978-0-691-05781-1 |pages=[https://archive.org/details/journeyfromcente0000zirk/page/120 120–127] |url-access=registration}}</ref> This releases an enormous amount of [[energy]], mostly [[radiant energy|radiated]] into [[outer space|space]] as [[electromagnetic radiation]] peaking in [[visible light]].<ref>{{Cite web |title=What Color is the Sun? |work=NASA |url=https://eclipse2017.nasa.gov/what-color-sun |access-date=6 April 2024 |archive-date=26 April 2024 |archive-url=https://web.archive.org/web/20240426130849/https://eclipse2017.nasa.gov/what-color-sun |url-status=live }}</ref><ref>{{Cite web |title=What Color is the Sun? |url=http://solar-center.stanford.edu/SID/activities/GreenSun.html |url-status=live |archive-url=https://web.archive.org/web/20171030154449/http://solar-center.stanford.edu/SID/activities/GreenSun.html |archive-date=30 October 2017 |access-date=23 May 2016 |publisher=[[Stanford University|Stanford]] Solar Center}}</ref>

Because the Sun fuses hydrogen at its core, it is a main-sequence star. More specifically, it is a [[G-type main-sequence star|G2-type main-sequence star]], where the type designation refers to its [[effective temperature]]. Hotter main-sequence stars are more luminous but shorter lived. The Sun's temperature is intermediate between that of the [[O-type main-sequence star|hottest stars]] and that of the coolest stars. Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as [[red dwarf]]s, make up about 75% of the [[Fusor (astronomy)|fusor]] stars in the [[Milky Way]].<ref>{{Cite journal |last1=Mejías |first1=Andrea |last2=Minniti |first2=Dante |last3=Alonso-García |first3=Javier |last4=Beamín |first4=Juan Carlos |last5=Saito |first5=Roberto K. |last6=Solano |first6=Enrique |year=2022 |title=VVVX near-IR photometry for 99 low-mass stars in the Gaia EDR3 Catalog of Nearby Stars |journal=Astronomy & Astrophysics |volume=660 |pages=A131 |arxiv=2203.00786 |bibcode=2022A&A...660A.131M |doi=10.1051/0004-6361/202141759 |s2cid=246842719}}</ref>

The Sun is a [[Population I stars|population I star]], having formed in the [[spiral arm]]s of the [[Milky Way]] galaxy. It has a higher abundance of elements heavier than hydrogen and helium ("[[metallicity|metals]]" in astronomical parlance) than the older population II stars in the [[galactic bulge]] and [[Galactic halo|halo]].<ref>{{Cite journal |last1=van Albada |first1=T.S. |last2=Baker |first2=Norman |date=1973 |title=On the Two Oosterhoff Groups of Globular Clusters |journal=[[The Astrophysical Journal]] |volume=185 |pages=477–498 |bibcode=1973ApJ...185..477V |doi=10.1086/152434 |doi-access=free}}</ref> Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the [[universe]] could be enriched with these atoms. The oldest stars contain few metals, whereas stars born later have more. This higher metallicity is thought to have been crucial to the Sun's development of a [[planetary system]] because the planets formed from the accretion of "metals".<ref>{{Cite journal |last=Lineweaver |first=Charles H. |date=9 March 2001 |title=An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect |journal=[[Icarus (journal)|Icarus]] |volume=151 |issue=2 |pages=307–313 |arxiv=astro-ph/0012399 |bibcode=2001Icar..151..307L |citeseerx=10.1.1.254.7940 |doi=10.1006/icar.2001.6607 |s2cid=14077895}}</ref>

{{Anchor|Interplanetary environment}}The region of space dominated by the Solar [[magnetosphere]] is the [[heliosphere]], which spans much of the Solar System. Along with [[Sunlight|light]], the Sun radiates a continuous stream of charged particles (a [[plasma (physics)|plasma]]) called the [[solar wind]]. This stream spreads outwards at speeds from {{Convert|900000|km/h|mph}} to {{Convert|2880000|km/h|mph}},<ref>{{Cite book |last=Kallenrode |first=May-Britt |url=https://www.worldcat.org/oclc/53443301 |title=Space Physics: An introduction to plasmas and particles in the heliosphere and magnetospheres |date=2004 |publisher=Springer |isbn=978-3-540-20617-0 |edition=3rd |location=Berlin |pages=150 |oclc=53443301 |access-date=1 April 2022 |archive-url=https://web.archive.org/web/20220420161223/https://www.worldcat.org/title/space-physics-an-introduction-to-plasmas-and-particles-in-the-heliosphere-and-magnetospheres/oclc/53443301 |archive-date=20 April 2022 |url-status=live}}</ref> filling the vacuum between the bodies of the Solar System. The result is a [[Vacuum|thin]], dusty atmosphere, called the [[interplanetary medium]], which extends to at least {{val|100|u=AU}}.<ref name="Voyager">{{Cite web |last=Steigerwald |first=Bill |date=24 May 2005 |title=Voyager Enters Solar System's Final Frontier |url=http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html |url-status=live |archive-url=https://web.archive.org/web/20200516082547/https://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html |archive-date=16 May 2020 |access-date=2 April 2007 |website=NASA}}</ref>

Activity on the Sun's surface, such as [[solar flare]]s and [[coronal mass ejection]]s, disturbs the heliosphere, creating [[space weather]] and causing [[geomagnetic storm]]s.<ref name="SunFlip">{{Cite web |last=Phillips |first=Tony |date=15 February 2001 |title=The Sun Does a Flip |url=https://science.nasa.gov/science-news/science-at-nasa/2001/ast15feb_1 |url-status=live |archive-url=https://web.archive.org/web/20220401050813/https://science.nasa.gov/science-news/science-at-nasa/2001/ast15feb_1 |archive-date=1 April 2022 |access-date=1 April 2022 |website=NASA Science: Share the Science}}</ref> Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into Earth's upper atmosphere, where its interactions create [[Aurora (astronomy)|aurorae]] seen near the [[Earth's magnetic field#Magnetic poles|magnetic poles]].<ref>{{Cite book |last1=Fraknoi |first1=Andrew |url=https://www.worldcat.org/oclc/961476196 |title=Astronomy |last2=Morrison |first2=David |last3=Wolff |first3=Sidney C. |last4=Beck |first4=John |date=2022 |publisher=[[OpenStax]] |isbn=978-1-947-17224-1 |location=Houston, Texas |chapter=15.4 Space weather |oclc=961476196 |display-authors=3 |access-date=9 March 2022 |orig-date=2016 |chapter-url=https://openstax.org/books/astronomy/pages/15-4-space-weather |archive-url=https://web.archive.org/web/20200719090803/http://worldcat.org/oclc/961476196 |archive-date=19 July 2020 |url-status=live}}</ref> The largest stable structure within the heliosphere is the [[heliospheric current sheet]], a spiral form created by the actions of the Sun's rotating magnetic field on the interplanetary medium.<ref>{{Cite web |date=22 April 2003 |title=A Star with two North Poles |url=https://science.nasa.gov/science-news/science-at-nasa/2003/22apr_currentsheet |url-status=live |archive-url=https://web.archive.org/web/20220401192948/https://science.nasa.gov/science-news/science-at-nasa/2003/22apr_currentsheet |archive-date=1 April 2022 |access-date=1 April 2022 |website=NASA Science: Share the Science}}</ref><ref>{{Cite journal |last=Riley |first=Pete |date=2002 |title=Modeling the heliospheric current sheet: Solar cycle variations |journal=[[Journal of Geophysical Research]] |volume=107 |issue=A7 |page=1136 |bibcode=2002JGRA..107.1136R |doi=10.1029/2001JA000299 |doi-access=free}}</ref>

== Inner Solar System ==
The inner Solar System is the region comprising the [[#Terrestrial planets|terrestrial planets]] and the [[asteroid]]s.<ref>{{Cite web |title=Inner Solar System |url=https://science.nasa.gov/solar-system/focus-areas/inner-solar-system |url-status=live |archive-url=https://web.archive.org/web/20220410004501/https://science.nasa.gov/solar-system/focus-areas/inner-solar-system |archive-date=10 April 2022 |access-date=2 April 2022 |website=NASA Science: Share the Science}}</ref> Composed mainly of [[silicate]]s and metals,<ref>{{Cite book |last1=Del Genio |first1=Anthony D. |title=Planetary Astrobiology |last2=Brain |first2=David |last3=Noack |first3=Lena |last4=Schaefer |first4=Laura |date=2020 |publisher=University of Arizona Press |isbn=978-0816540655 |editor-last=Meadows |editor-first=Victoria S. |page=420 |chapter=The Inner Solar System's Habitability Through Time |bibcode=2018arXiv180704776D |author-link4=Laura K. Schaefer |editor-last2=Arney |editor-first2=Giada N. |editor-last3=Schmidt |editor-first3=Britney |editor-last4=Des Marais |editor-first4=David J. |arxiv=1807.04776}}</ref> the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn. This region is within the [[Frost line (astrophysics)|frost line]], which is a little less than {{val|5|u=AU}} from the Sun.<ref name="Levison2003"/>

=== Inner planets<span class="anchor" id="Terrestrial planets"></span> ===
{{Main|Terrestrial planet}}
[[File:Terrestrial planet sizes 3.jpg|right|thumb|alt=Venus and Earth about the same size, Mars is about 0.55 times as big and Mercury is about 0.4 times as big|The four terrestrial planets [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]] and [[Mars]]]]
The four terrestrial or inner planets have dense, rocky compositions, few or no [[natural satellite|moons]], and no [[planetary ring|ring systems]]. They are composed largely of [[Refractory (planetary science)|refractory]] minerals such as [[silicates]]{{Mdash}}which form their [[crust (geology)|crusts]] and [[mantle (geology)|mantles]]{{Mdash}}and metals such as iron and nickel which form their [[planetary core|cores]]. Three of the four inner planets (Venus, Earth, and Mars) have [[atmosphere]]s substantial enough to generate weather; all have impact craters and [[tectonics|tectonic]] surface features, such as [[rift valley]]s and volcanoes.<ref name="Ryden">{{Cite journal |last=Ryden |first=Robert |date=December 1999 |title=Astronomical Math |url=https://pubs.nctm.org/view/journals/mt/92/9/article-p786.xml |url-status=live |journal=The Mathematics Teacher |volume=92 |issue=9 |pages=786–792 |doi=10.5951/MT.92.9.0786 |issn=0025-5769 |jstor=27971203 |archive-url=https://web.archive.org/web/20220412010049/https://pubs.nctm.org/view/journals/mt/92/9/article-p786.xml |archive-date=12 April 2022 |access-date=29 March 2022}}</ref>

* {{Visible anchor|Mercury|text=[[Mercury (planet)|Mercury]]}} (0.31–0.59&nbsp;AU from the Sun)<ref name="nasa-factsheet" group="D">{{Cite web |last=Williams |first=David |date=27 December 2021 |title=Planetary Fact Sheet - Metric |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet |access-date=11 December 2022 |publisher=[[Goddard Space Flight Center]] |archive-date=18 August 2011 |archive-url=https://web.archive.org/web/20110818181734/http://nssdc.gsfc.nasa.gov/planetary/factsheet/ |url-status=live }}</ref> is the smallest planet in the Solar System. Its surface is grayish, with an expansive [[rupes]] (cliff) system generated from [[thrust fault]]s and bright [[ray system]]s formed by [[Ejecta|impact event remnants]].<ref>{{Cite journal |last1=Watters |first1=Thomas R. |last2=Solomon |first2=Sean C. |last3=Robinson |first3=Mark S. |last4=Head |first4=James W. |last5=André |first5=Sarah L. |last6=Hauck |first6=Steven A. |last7=Murchie |first7=Scott L. |date=August 2009 |title=The tectonics of Mercury: The view after MESSENGER's first flyby |journal=Earth and Planetary Science Letters |language=en |volume=285 |issue=3–4 |pages=283–296 |bibcode=2009E&PSL.285..283W |doi=10.1016/j.epsl.2009.01.025}}</ref> The surface has widely varying temperature, with the [[equator]]ial regions ranging from {{convert|-170|C|F|sigfig=2}} at night to {{convert|420|C|F|sigfig=2}} during sunlight. In the past, Mercury was volcanically active, producing smooth [[basalt]]ic plains similar to the Moon.<ref name=Head_et_al_1981>{{cite journal |last1=Head |first1=James W. |author-link1=James W. Head |last2=Solomon |first2=Sean C. |author-link2=Sean Solomon |year=1981 |title=Tectonic Evolution of the Terrestrial Planets |url=http://www.planetary.brown.edu/pdfs/323.pdf |url-status=dead |journal=Science |volume=213 |issue=4503 |pages=62–76 |bibcode=1981Sci...213...62H |citeseerx=10.1.1.715.4402 |doi=10.1126/science.213.4503.62 |pmid=17741171 |archive-url=https://web.archive.org/web/20180721153426/http://www.planetary.brown.edu/pdfs/323.pdf |archive-date=21 July 2018 |access-date=25 October 2017 |hdl=2060/20020090713}}</ref> It is likely that Mercury has a silicate crust and a large iron core.<ref>{{cite web |date=21 March 2012 |editor-last=Talbert |editor-first=Tricia |title=MESSENGER Provides New Look at Mercury's Surprising Core and Landscape Curiosities |url=https://www.nasa.gov/mission_pages/messenger/media/PressConf20120321.html |url-status=dead |archive-url=https://web.archive.org/web/20190112170032/https://www.nasa.gov/mission_pages/messenger/media/PressConf20120321.html |archive-date=12 January 2019 |access-date=20 April 2018 |publisher=NASA}}</ref><ref name="Margot2012">{{cite journal |last1=Margot |first1=Jean-Luc |last2=Peale |first2=Stanton J. |last3=Solomon |first3=Sean C. |last4=Hauck |first4=Steven A. |last5=Ghigo |first5=Frank D. |last6=Jurgens |first6=Raymond F. |last7=Yseboodt |first7=Marie |last8=Giorgini |first8=Jon D. |last9=Padovan |first9=Sebastiano |last10=Campbell |first10=Donald B. |year=2012 |title=Mercury's moment of inertia from spin and gravity data |journal=Journal of Geophysical Research: Planets |volume=117 |issue=E12 |pages=n/a |bibcode=2012JGRE..117.0L09M |citeseerx=10.1.1.676.5383 |doi=10.1029/2012JE004161 |issn=0148-0227 |s2cid=22408219}}</ref> Mercury has a very tenuous atmosphere, consisting of [[Solar wind|solar-wind]] particles and ejected atoms.<ref>{{Cite journal |last1=Domingue |first1=Deborah L. |last2=Koehn |first2=Patrick L. |last3=Killen |first3=Rosemary M. |last4=Sprague |first4=Ann L. |last5=Sarantos |first5=Menelaos |last6=Cheng |first6=Andrew F. |last7=Bradley |first7=Eric T. |last8=McClintock |first8=William E. |display-authors=2 |date=2009 |title=Mercury's Atmosphere: A Surface-Bounded Exosphere |journal=Space Science Reviews |volume=131 |issue=1–4 |pages=161–186 |bibcode=2007SSRv..131..161D |doi=10.1007/s11214-007-9260-9 |s2cid=121301247 |quote=The composition of Mercury's exosphere, with its abundant H and He, clearly indicates a strong solar wind source. Once solar wind plasma and particles gain access to the magnetosphere, they predominantly precipitate to the surface, where solar wind species are neutralized, thermalized, and released again into the exosphere. Moreover, bombardment of the surface by solar wind particles, especially energetic ions, contributes to ejection of neutral species from the surface into the exosphere (via "sputtering") as well as other chemical and physical surface modification processes.}}</ref> Mercury has no natural satellites.<ref name="spaceplace.nasa.gov">{{Cite web |title=How Many Moons Does Each Planet Have? {{!}} NASA Space Place – NASA Science for Kids |url=https://spaceplace.nasa.gov/how-many-moons/en/ |access-date=21 April 2024 |website=spaceplace.nasa.gov |archive-date=21 April 2024 |archive-url=https://web.archive.org/web/20240421061913/https://spaceplace.nasa.gov/how-many-moons/en/ |url-status=live }}</ref>
* {{Visible anchor|Venus|text=[[Venus]]}} (0.72–0.73&nbsp;AU)<ref name="nasa-factsheet" group="D" /> has a reflective, whitish atmosphere that is mainly composed of [[carbon dioxide]]. At the surface, the atmospheric pressure is ninety times as dense as on Earth's sea level.<ref name="u3r1a">{{cite journal |last1=Lebonnois |first1=Sebastien |last2=Schubert |first2=Gerald |date=26 June 2017 |title=The deep atmosphere of Venus and the possible role of density-driven separation of CO2 and N2 |url=https://hal.archives-ouvertes.fr/hal-01635402/file/deepatm_persp_rev2.pdf |url-status=live |journal=Nature Geoscience |publisher=Springer Science and Business Media LLC |volume=10 |issue=7 |pages=473–477 |bibcode=2017NatGe..10..473L |doi=10.1038/ngeo2971 |issn=1752-0894 |s2cid=133864520 |archive-url=https://web.archive.org/web/20190504081028/https://hal.archives-ouvertes.fr/hal-01635402/file/deepatm_persp_rev2.pdf |archive-date=4 May 2019 |access-date=11 August 2023}}</ref> Venus has a surface temperatures over {{Cvt|400|C|F}}, mainly due to the amount of [[greenhouse gas]]es in the atmosphere.<ref>{{Cite thesis |last=Bullock |first=Mark Alan |title=The Stability of Climate on Venus |date=1997 |degree=PhD |publisher=Southwest Research Institute |url=http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |access-date=26 December 2006 |url-status=dead |archive-url=https://web.archive.org/web/20070614202751/http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |archive-date=14 June 2007}}</ref> The planet lacks a protective magnetic field to protect against [[Atmospheric stripping|stripping]] by the solar wind, which suggests that its atmosphere is sustained by volcanic activity.<ref>{{Cite web |last=Rincon |first=Paul |date=1999 |title=Climate Change as a Regulator of Tectonics on Venus |url=http://www.boulder.swri.edu/~bullock/Homedocs/Science2_1999.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070614202807/http://www.boulder.swri.edu/~bullock/Homedocs/Science2_1999.pdf |archive-date=14 June 2007 |access-date=19 November 2006 |website=Johnson Space Center Houston, TX, Institute of Meteoritics, University of New Mexico, Albuquerque, NM}}</ref> Its surface displays extensive evidence of volcanic activity with stagnant [[lid tectonics]].<ref>{{Cite journal |last1=Elkins-Tanton |first1=L. T. |last2=Smrekar |first2=S. E. |last3=Hess |first3=P. C. |last4=Parmentier |first4=E. M. |date=March 2007 |title=Volcanism and volatile recycling on a one-plate planet: Applications to Venus |journal=Journal of Geophysical Research |volume=112 |issue=E4 |bibcode=2007JGRE..112.4S06E |doi=10.1029/2006JE002793 |id=E04S06 |doi-access=free}}</ref> Venus has no natural satellites.<ref name="spaceplace.nasa.gov"/>
* {{Visible anchor|Earth|text=[[Earth]]}} (0.98–1.02&nbsp;AU)<ref name="nasa-factsheet" group="D" /> is the only place in the universe where [[life]] and [[Water distribution on Earth|surface liquid water]] are known to exist.<ref name="life">{{Cite web |title=What are the characteristics of the Solar System that lead to the origins of life? |url=https://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1 |url-status=dead |archive-url=https://web.archive.org/web/20100408055814/http://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1 |archive-date=8 April 2010 |access-date=30 August 2011 |publisher=NASA Science (Big Questions)}}</ref> Earth's atmosphere contains 78% [[nitrogen]] and 21% [[oxygen]], which is the result of the presence of life.<ref name="handbook">{{Cite book |title=[[CRC Handbook of Chemistry and Physics]] |publisher=CRC Press |year=2016–2017 |isbn=978-1-4987-5428-6 |editor-last=Haynes |editor-first=H. M. |edition=97th |page=14{{Hyphen}}3<!-- the page ref itself is hyphenated -->}}</ref><ref name="NYT-20131003">{{Cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |date=3 October 2013 |title=Earth's Oxygen: A Mystery Easy to Take for Granted |work=[[The New York Times]] |url=https://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |url-access=limited |access-date=3 October 2013 |archive-url=https://web.archive.org/web/20131003121909/http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |archive-date=3 October 2013}}</ref> The planet has a complex [[climate]] and [[weather]] system, with conditions differing drastically between [[climate region]]s.<ref name="climate_zones">{{cite web |author=Staff |title=Climate Zones |url=http://www.ace.mmu.ac.uk/eae/climate/older/Climate_Zones.html |archive-url=https://web.archive.org/web/20100808131632/http://www.ace.mmu.ac.uk/eae/climate/older/Climate_Zones.html |archive-date=8 August 2010 |access-date=24 March 2007 |publisher=UK Department for Environment, Food and Rural Affairs}}</ref> The solid surface of Earth is dominated by green [[vegetation]], [[Hot deserts|deserts]] and white [[ice sheet]]s.<ref name="Carlowicz Simmon 2019">{{cite web |last1=Carlowicz |first1=Michael |last2=Simmon |first2=Robert |date=15 July 2019 |title=Seeing Forests for the Trees and the Carbon: Mapping the World's Forests in Three Dimensions |url=https://earthobservatory.nasa.gov/features/ForestCarbon#:~:text=They%20cover%20about%2030%20percent,percent%20of%20the%20Earth's%20land. |access-date=31 December 2022 |website=NASA Earth Observatory |archive-date=31 December 2022 |archive-url=https://web.archive.org/web/20221231005400/https://earthobservatory.nasa.gov/features/ForestCarbon#:~:text=They%20cover%20about%2030%20percent,percent%20of%20the%20Earth's%20land. |url-status=live }}</ref><ref name="Cain 2010">{{cite web |last=Cain |first=Fraser |date=1 June 2010 |title=What Percentage of the Earth's Land Surface is Desert? |url=https://www.universetoday.com/65639/what-percentage-of-the-earths-land-surface-is-desert/ |access-date=3 January 2023 |website=Universe Today |archive-date=3 January 2023 |archive-url=https://web.archive.org/web/20230103153344/https://www.universetoday.com/65639/what-percentage-of-the-earths-land-surface-is-desert/ |url-status=live }}</ref><ref name="National Geographic Society 2006">{{cite web |date=6 August 2006 |title=Ice Sheet |url=https://education.nationalgeographic.org/resource/ice-sheet/ |access-date=3 January 2023 |website=National Geographic Society |archive-date=27 November 2023 |archive-url=https://web.archive.org/web/20231127174259/https://education.nationalgeographic.org/resource/ice-sheet/ |url-status=live }}</ref> Earth's surface is shaped by [[plate tectonics]] that formed the continental masses.<ref name=Head_et_al_1981/> Earth's planetary [[magnetosphere]] shields the surface from radiation, limiting [[atmospheric stripping]] and maintaining life habitability.<ref>{{Cite book |last=Pentreath |first=R. J. |url=https://books.google.com/books?id=avRVEAAAQBAJ&pg=PA94 |title=Radioecology: Sources and Consequences of Ionising Radiation in the Environment |date=2021 |publisher=Cambridge University Press |isbn=978-1009040334 |pages=94–97 |access-date=12 April 2022 |archive-url=https://web.archive.org/web/20220420161217/https://www.google.com/books/edition/Radioecology/avRVEAAAQBAJ?hl=en&gbpv=1&pg=PA94 |archive-date=20 April 2022 |url-status=live}}</ref>
** The [[Moon]] is Earth's only natural satellite.<ref>{{Cite web |title=Facts About Earth - NASA Science |url=https://science.nasa.gov/earth/facts/ |access-date=11 January 2024 |website=NASA Science |language=en}}</ref> Its diameter is one-quarter the size of Earth's.<ref name="Metzger2021">{{Citation |last1=Metzger |first1=Philip |title=Moons are planets: Scientific usefulness versus cultural teleology in the taxonomy of planetary science |date=2021 |journal=[[Icarus (journal)|Icarus]] |volume=374 |page=114768 |arxiv=2110.15285 |bibcode=2022Icar..37414768M |doi=10.1016/j.icarus.2021.114768 |s2cid=240071005 |last2=Grundy |first2=Will |last3=Sykes |first3=Mark |last4=Stern |first4=Alan |last5=Bell |first5=James |last6=Detelich |first6=Charlene |last7=Runyon |first7=Kirby |last8=Summers |first8=Michael |author-link1=Philip T. Metzger}}</ref> Its surface is covered in [[Lunar soil|very fine regolith]] and dominated by [[impact crater]]s.<ref>{{cite web |date=30 January 2006 |title=The Smell of Moondust |url=https://science.nasa.gov/headlines/y2006/30jan_smellofmoondust.htm |url-status=dead |archive-url=https://web.archive.org/web/20100308112332/http://science.nasa.gov/headlines/y2006/30jan_smellofmoondust.htm |archive-date=8 March 2010 |access-date=15 March 2010 |publisher=NASA}}</ref><ref>{{cite book |last=Melosh |first=H. J. |title=Impact cratering: A geologic process |date=1989 |publisher=[[Oxford University Press]] |isbn=978-0-19-504284-9}}</ref> Large dark patches on the Moon, [[Lunar mare|maria]], are formed from past volcanic activity.<ref>{{cite web |last=Norman |first=M. |date=21 April 2004 |title=The Oldest Moon Rocks |url=http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |url-status=live |archive-url=https://web.archive.org/web/20070418152325/http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |archive-date=18 April 2007 |access-date=12 April 2007 |work=Planetary Science Research Discoveries |publisher=Hawai'i Institute of Geophysics and Planetology}}</ref> The Moon's atmosphere is extremely thin, consisting of a [[partial vacuum]] with particle densities of under 10<sup>7</sup> per cm<sup>−3</sup>.<ref>{{cite book |last=Globus |first=Ruth |title=Space Settlements: A Design Study |date=1977 |publisher=NASA |editor=Richard D. Johnson & Charles Holbrow |chapter=Chapter 5, Appendix J: Impact Upon Lunar Atmosphere |access-date=17 March 2010 |chapter-url=http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |archive-url=https://web.archive.org/web/20100531205037/http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |archive-date=31 May 2010 |url-status=dead}}</ref> 
* {{Visible anchor|Mars|text=[[Mars]]}} (1.38–1.67&nbsp;AU)<ref name="nasa-factsheet" group="D" /> has a radius about half of that of Earth.<ref name="Seidelmann2007">{{cite journal |last1=Seidelmann |first1=P. Kenneth |last2=Archinal |first2=Brent A. |last3=A'Hearn<!-- written A'hearn here, mostly A'Hearn elsewhere --> |first3=Michael F. |last4=Conrad |first4=Albert R. |last5=Consolmagno |first5=Guy J. |last6=Hestroffer |first6=Daniel |last7=Hilton |first7=James L. |last8=Krasinsky |first8=Georgij A. |last9=Neumann |first9=Gregory A. |last10=Oberst |first10=Jürgen |last11=Stooke |first11=Philip J. |last12=Tedesco |first12=Edward F. |last13=Tholen |first13=David J. |last14=Thomas |first14=Peter C. |last15=Williams |first15=Iwan P. |year=2007 |title=Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006 |journal=Celestial Mechanics and Dynamical Astronomy |volume=98 |issue=3 |pages=155–180 |bibcode=2007CeMDA..98..155S |doi=10.1007/s10569-007-9072-y |ref={{sfnRef|Seidelmann Archinal A'hearn et al.|2007}} |doi-access=free}}</ref> Most of the planet is red due to [[iron(III) oxide|iron oxide]] in Martian soil,<ref>{{Cite journal |last=Peplow |first=Mark |date=6 May 2004 |title=How Mars got its rust |url=http://www.nature.com/articles/news040503-6 |url-status=live |journal=Nature |language=en |pages=news040503–6 |doi=10.1038/news040503-6 |issn=0028-0836 |archive-url=https://web.archive.org/web/20220407105832/https://www.nature.com/articles/news040503-6 |archive-date=7 April 2022 |access-date=9 April 2022}}</ref> and the polar regions are covered in [[Martian polar ice caps|white ice caps]] made of water and [[carbon dioxide]].<ref>{{Cite web |title=Polar Caps |url=https://marsed.asu.edu/mep/ice/polar-caps |access-date=6 January 2022 |website=Mars Education at Arizona State University |archive-date=28 May 2021 |archive-url=https://web.archive.org/web/20210528133135/https://marsed.asu.edu/mep/ice/polar-caps |url-status=live }}</ref> Mars has an atmosphere composed mostly of carbon dioxide, with surface pressure 0.6% of that of Earth, which is sufficient to support some weather phenomena.<ref>{{Cite book |last1=Gatling |first1=David C. |title=Encyclopaedia of the Solar System |last2=Leovy |first2=Conway |date=2007 |editor-last=Lucy-Ann McFadden |pages=301–314 |chapter=Mars Atmosphere: History and Surface Interactions |display-editors=etal}}</ref> During the Mars year (687 Earth days), there are large surface temperature swings on the surface between {{Cvt|-78.5|C|F}} to {{Cvt|5.7|C|F}}. The surface is peppered with volcanoes and [[rift valley]]s, and has a rich collection of [[mineral]]s.<ref>{{Cite web |last=Noever |first=David |date=2004 |title=Modern Martian Marvels: Volcanoes? |url=https://www.astrobio.net/mars/modern-martian-marvels-volcanoes |url-status=dead |archive-url=https://web.archive.org/web/20200314112555/https://www.astrobio.net/mars/modern-martian-marvels-volcanoes |archive-date=14 March 2020 |access-date=23 July 2006 |website=NASA Astrobiology Magazine}}</ref><ref name="ismars">[http://mars.jpl.nasa.gov/msl/multimedia/videos/index.cfm?v=29&a=2 NASA – ''Mars in a Minute: Is Mars Really Red?''] {{Webarchive|url=https://web.archive.org/web/20140720135450/http://mars.jpl.nasa.gov/msl/multimedia/videos/index.cfm?v=29&a=2|date=20 July 2014}} ([http://mars.jpl.nasa.gov/multimedia/videos/movies/miam20111110/miam20111110.pdf Transcript] {{Webarchive|url=https://web.archive.org/web/20151106174558/http://mars.jpl.nasa.gov/multimedia/videos/movies/miam20111110/miam20111110.pdf|date=6 November 2015}}) {{PD-notice}}</ref> Mars has a highly [[Planetary differentiation|differentiated]] internal structure, and lost its magnetosphere 4&nbsp;billion years ago.<ref name="Nimmo 2005">{{cite journal |last1=Nimmo |first1=Francis |last2=Tanaka |first2=Ken |year=2005 |title=Early Crustal Evolution of Mars |journal=Annual Review of Earth and Planetary Sciences |volume=33 |issue=1 |pages=133–161 |bibcode=2005AREPS..33..133N |doi=10.1146/annurev.earth.33.092203.122637 |s2cid=45843366}}</ref><ref name="swind">{{cite web |last=Philips |first=Tony |date=31 January 2001 |title=The Solar Wind at Mars |url=https://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |url-status=dead |archive-url=https://web.archive.org/web/20110818180040/https://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |archive-date=18 August 2011 |access-date=22 April 2022 |website=Science@NASA}} {{PD-notice}}</ref> [[Moons of Mars|Mars has two tiny moons]]:<ref name="NYT-20200725">{{cite news |last=Andrews |first=Robin George |date=25 July 2020 |title=Why the 'Super Weird' Moons of Mars Fascinate Scientists - What's the big deal about little Phobos and tinier Deimos? |url=https://www.nytimes.com/2020/07/25/science/mars-moons-phobos-deimos.html |url-status=live |archive-url=https://web.archive.org/web/20200725094039/https://www.nytimes.com/2020/07/25/science/mars-moons-phobos-deimos.html |archive-date=25 July 2020 |access-date=25 July 2020 |work=[[The New York Times]]}}</ref>
** [[Phobos (moon)|Phobos]] is Mars's inner moon. It is a small, irregularly shaped object with a mean radius of {{convert|11|km|abbr=on|sigfig=1}}. Its surface is very unreflective and dominated by impact craters.<ref name="jplssd" group="D">{{cite web |date=13 July 2006 |title=Planetary Satellite Physical Parameters |url=http://ssd.jpl.nasa.gov/?sat_phys_par |access-date=29 January 2008 |publisher=[[JPL]] (Solar System Dynamics) |archive-date=1 November 2013 |archive-url=https://web.archive.org/web/20131101144111/http://ssd.jpl.nasa.gov/?sat_phys_par |url-status=live }}</ref><ref>{{cite web |date=12 January 2004 |title=Phobos |url=http://www.bbc.co.uk/science/space/solarsystem/mars/phobos.shtml |url-status=dead |archive-url=https://web.archive.org/web/20090422160500/http://www.bbc.co.uk/science/space/solarsystem/mars/phobos.shtml |archive-date=22 April 2009 |access-date=19 July 2021 |work=[[BBC Online]]}}</ref> In particular, Phobos's surface has a very large [[Stickney (crater)|Stickney impact crater]] that is roughly {{convert|4.5|km|mi|abbr=on}} in radius.<ref>{{cite web |title=Stickney Crater-Phobos |url=http://www.solarviews.com/cap/mars/phobos2.htm |quote=One of the most striking features of Phobos, aside from its irregular shape, is its giant crater Stickney. Because Phobos is only {{Convert|28|by|20|km||sp=us}}, it must have been nearly shattered from the force of the impact that caused the giant crater. Grooves that extend across the surface from Stickney appear to be surface fractures caused by the impact. |access-date=21 April 2024 |archive-date=3 November 2011 |archive-url=https://web.archive.org/web/20111103010644/http://www.solarviews.com/cap/mars/phobos2.htm |url-status=live }}</ref> 
** [[Deimos (moon)|Deimos]] is Mars's outer moon. Like Phobos, it is irregularly shaped, with a mean radius of {{convert|6|km|mi|abbr=on|sigfig=1}} and its surface reflects little light.<ref name="Horizons-Deimos" group="D">{{cite web |date=21 September 2013 |title=HORIZONS Web-Interface |url=http://ssd.jpl.nasa.gov/?horizons |access-date=4 December 2013 |publisher=NASA |archive-date=28 March 2007 |archive-url=https://web.archive.org/web/20070328180634/http://ssd.jpl.nasa.gov/?horizons |url-status=live }}</ref><ref name="JPLSSD" group="D">{{cite web |date=13 July 2006 |title=Planetary Satellite Physical Parameters |url=http://ssd.jpl.nasa.gov/?sat_phys_par |access-date=29 January 2008 |publisher=[[Jet Propulsion Laboratory]] (Solar System Dynamics) |archive-date=1 November 2013 |archive-url=https://web.archive.org/web/20131101144111/http://ssd.jpl.nasa.gov/?sat_phys_par |url-status=live }}</ref> However, the surface of Deimos is noticeably smoother than Phobos because the regolith partially covers the impact craters.<ref>{{Cite web |date=6 June 2023 |title=Deimos |url=https://www.britannica.com/place/Deimos-moon-of-Mars |access-date=21 April 2024 |website=Britannica |language=en |quote=It thus appears smoother than Phobos because its craters lie partially buried under this loose material. |archive-date=12 November 2018 |archive-url=https://web.archive.org/web/20181112023547/https://www.britannica.com/place/Deimos-moon-of-Mars |url-status=live }}</ref>

===Asteroids ===
{{Main|Asteroid}}
[[File:Inner solar system objects top view for wiki.png|right|thumb|alt=Asteroid populations depicted: near-Earth asteroids, Earth trojans, Mars trojans, main asteroid belt, Jupiter trojans, Jupiter Greeks, Jupiter Hilda's triangle|Overview of the inner Solar System up to Jupiter's orbit]]Asteroids except for the largest, Ceres, are classified as [[small Solar System bodies]] and are composed mainly of [[carbon]]aceous, refractory rocky and metallic minerals, with some ice.<ref>{{Cite web |date=2006 |title=IAU Planet Definition Committee |url=http://www.iau.org/public_press/news/release/iau0601/newspaper |url-status=dead |archive-url=https://web.archive.org/web/20090603001603/http://www.iau.org/public_press/news/release/iau0601/newspaper |archive-date=3 June 2009 |access-date=1 March 2009 |publisher=International Astronomical Union}}</ref><ref>{{Cite web |title=Are Kuiper Belt Objects asteroids? Are large Kuiper Belt Objects planets? |url=http://curious.astro.cornell.edu/question.php?number=601 |url-status=dead |archive-url=https://web.archive.org/web/20090103110110/http://curious.astro.cornell.edu/question.php?number=601 |archive-date=3 January 2009 |access-date=1 March 2009 |publisher=[[Cornell University]]}}</ref> They range from a few meters to hundreds of kilometers in size. {{Visible anchor|Asteroid groups|text=Many asteroids are divided into [[asteroid group]]s and [[Asteroid family|families]]}} based on their orbital characteristics. Some [[Minor-planet moon|asteroids have natural satellites that orbit them]], that is, asteroids that orbit larger asteroids.<ref>{{Cite journal |last1=Snodgrass |first1=Colin |last2=Agarwal |first2=Jessica |last3=Combi |first3=Michael |last4=Fitzsimmons |first4=Alan |last5=Guilbert-Lepoutre |first5=Aurelie |last6=Hsieh |first6=Henry H. |last7=Hui |first7=Man-To |last8=Jehin |first8=Emmanuel |last9=Kelley |first9=Michael S. P. |last10=Knight |first10=Matthew M. |last11=Opitom |first11=Cyrielle |date=November 2017 |title=The Main Belt Comets and ice in the Solar System |url=http://link.springer.com/10.1007/s00159-017-0104-7 |url-status=live |journal=The Astronomy and Astrophysics Review |language=en |volume=25 |issue=1 |page=5 |arxiv=1709.05549 |bibcode=2017A&ARv..25....5S |doi=10.1007/s00159-017-0104-7 |issn=0935-4956 |s2cid=7683815 |archive-url=https://web.archive.org/web/20220420161227/https://idp.springer.com/favicon.ico |archive-date=20 April 2022 |access-date=9 March 2022}}</ref>

* [[List of Mercury-crossing minor planets|Mercury-crossing asteroids]] are those with [[perihelia]] within the orbit of Mercury. At least 362 are known to date, and include the closest objects to the Sun known in the Solar System.<ref name="JPLcrosserlist">[http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=ast;obj_numbered=all;OBJ_field=0;ORB_field=0;c1_group=ORB;c1_item=Bi;c1_op=%3C;c1_value=0.3075;table_format=HTML;max_rows=200;format_option=comp;c_fields=BgBhBiBjBnBsChAcCq;.cgifields=format_option;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=BiA List of asteroids with q<0.3075 AU generated by the JPL Small-Body Database Search Engine] {{Webarchive|url=https://web.archive.org/web/20160303213657/http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all&obj_kind=ast&obj_numbered=all&OBJ_field=0&ORB_field=0&c1_group=ORB&c1_item=Bi&c1_op=%3C&c1_value=0.3075&table_format=HTML&max_rows=200&format_option=comp&c_fields=BgBhBiBjBnBsChAcCq&.cgifields=format_option&.cgifields=ast_orbit_class&.cgifields=table_format&.cgifields=obj_kind&.cgifields=obj_group&.cgifields=obj_numbered&.cgifields=com_orbit_class&query=1&c_sort=BiA |date=3 March 2016 }} Retrieved 30 May 2012</ref> No [[vulcanoid]]s, asteroids between the orbit of Mercury and the Sun, have been discovered.<ref>{{Cite journal |last1=Durda |first1=D .D. |last2=Stern |first2=S. A. |last3=Colwell |first3=W. B. |last4=Parker |first4=J. W. |last5=Levison |first5=H. F. |last6=Hassler |first6=D. M. |date=2004 |title=A New Observational Search for Vulcanoids in SOHO/LASCO Coronagraph Images |journal=[[Icarus (journal)|Icarus]] |volume=148 |issue=1 |pages=312–315 |bibcode=2000Icar..148..312D |doi=10.1006/icar.2000.6520}}</ref><ref name="Steffl2013">{{Cite journal |last1=Steffl |first1=A. J. |last2=Cunningham |first2=N. J. |last3=Shinn |first3=A. B. |last4=Stern |first4=S. A. |date=2013 |title=A Search for Vulcanoids with the STEREO Heliospheric Imager |journal=Icarus |volume=233 |issue=1 |pages=48–56 |arxiv=1301.3804 |bibcode=2013Icar..223...48S |doi=10.1016/j.icarus.2012.11.031 |s2cid=118612132}}</ref> As of 2024, one asteroid has been discovered to orbit completely within Venus's orbit, [[594913 ꞌAylóꞌchaxnim]].<ref>{{cite journal |last1=Bolin |first1=Bryce T. |last2=Ahumada |first2=T. |last3=van Dokkum |first3=P. |last4=Fremling |first4=C. |last5=Granvik |first5=M. |last6=Hardegree-Ullmann |first6=K. K. |last7=Harikane |first7=Y. |last8=Purdum |first8=J. N. |last9=Serabyn |first9=E. |last10=Southworth |first10=J. |last11=Zhai |first11=C. |date=November 2022 |title=The discovery and characterization of (594913) 'Ayló'chaxnim, a kilometre sized asteroid inside the orbit of Venus |url=https://academic.oup.com/mnrasl/article/517/1/L49/6665933 |journal=[[Monthly Notices of the Royal Astronomical Society Letters]] |volume=517 |issue=1 |pages=L49–L54 |arxiv=2208.07253 |bibcode=2022MNRAS.517L..49B |doi=10.1093/mnrasl/slac089 |access-date=1 October 2022 |doi-access=free |archive-date=1 October 2022 |archive-url=https://web.archive.org/web/20221001070557/https://academic.oup.com/mnrasl/article/517/1/L49/6665933 |url-status=live }}</ref>
* [[Venus-crossing asteroid]]s are those that cross the orbit of Venus. There are 2,809 as of 2015.<ref name=jpello/>
* [[near-Earth object|Near-Earth asteroids]] have orbits that approach relatively close to Earth's orbit,<ref name="MorbidelliAstIII">{{Cite book |last1=Morbidelli |first1=A. |last2=Bottke |first2=W.F. |last3=Froeschlé |first3=Ch. |last4=Michel |first4=P. |date=January 2002 |editor2-last=A. Cellino |editor3-last=P. Paolicchi |editor4-last=R.P. Binzel |title=Origin and Evolution of Near-Earth Objects |url=http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf |url-status=live |journal=Asteroids III |pages=409–422 |publisher=University of Arizona Press |bibcode=2002aste.book..409M |doi=10.2307/j.ctv1v7zdn4.33 |isbn=978-0-8165-2281-1 |archive-url=https://web.archive.org/web/20170809014123/http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf |archive-date=9 August 2017 |access-date=30 August 2009 |editor=W.F. Bottke Jr.}}</ref> and some of them are [[potentially hazardous object]]s because they might collide with Earth in the future.<ref name="CNEOS-Basics">{{Cite web |title=NEO Basics – Potentially Hazardous Asteroids (PHAs) |url=https://cneos.jpl.nasa.gov/about/neo_groups.html |url-status=live |archive-url=https://web.archive.org/web/20211111141623/https://cneos.jpl.nasa.gov/about/neo_groups.html |archive-date=11 November 2021 |access-date=10 March 2022 |publisher=CNEOS NASA/JPL}}</ref><ref name="NEO-groups">{{cite web |last1=Baalke |first1=Ron |title=Near-Earth Object Groups |url=http://neo.jpl.nasa.gov/neo/groups.html |url-status=dead |archive-url=https://web.archive.org/web/20020202160655/http://neo.jpl.nasa.gov/neo/groups.html |archive-date=2 February 2002 |access-date=11 November 2016 |website=[[Jet Propulsion Laboratory]] |publisher=[[NASA]]}}</ref> There are over 37.000 known as of 2024.<ref name="neo-jpl-stats" /> A number of solar-orbiting [[meteoroid]]s were large enough to be tracked in space before striking Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of Earth.<ref name="BROWN02">{{cite news |first=Richard |last=Monastersky |title=The Call of Catastrophes |work=Science News Online |date=March 1, 1997  |url=https://www.sciencenews.org/archive/call-catastrophes |access-date=January 2, 2025 |url-status=live |archive-url=https://web.archive.org/web/20040313165341/http://www.sciencenews.org/pages/sn_arc97/75th/rm_essay.htm |archive-date=March 13, 2004 }}</ref>
* [[Mars-crossing asteroids]] are those with perhihelia above 1.3&nbsp;AU which cross the orbit of Mars.<ref>{{cite journal|journal=Astronomy & Astrophysics|volume=391|pages=757–765|year=2002|doi=10.1051/0004-6361:20020834|title=Spectral properties of Mars-crossers and near-Earth objects|author=C. A. Angeli - D. Lazzaro|issue=2 }}</ref> As of 2024, NASA lists 26,182 confirmed Mars-crossing asteroids.<ref name=jpello>{{cite web|title=Small-Body Database Query|url=https://ssd.jpl.nasa.gov/tools/sbdb_query.html#!|work=NASA|accessdate=3 June 2024|archive-date=27 September 2021|archive-url=https://web.archive.org/web/20210927184129/https://ssd.jpl.nasa.gov/tools/sbdb_query.html#!|url-status=live}}</ref>

====Asteroid belt====
The [[asteroid belt]] occupies a torus-shaped region between 2.3 and {{val|3.3|u=AU}} from the Sun, which lies between the orbits of Mars and Jupiter. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter.<ref>{{Cite journal |last1=Petit |first1=J.-M. |last2=Morbidelli |first2=A. |last3=Chambers |first3=J. |date=2001 |title=The Primordial Excitation and Clearing of the Asteroid Belt |url=http://www.gps.caltech.edu/classes/ge133/reading/asteroids.pdf |url-status=dead |journal=[[Icarus (journal)|Icarus]] |volume=153 |issue=2 |pages=338–347 |bibcode=2001Icar..153..338P |doi=10.1006/icar.2001.6702 |archive-url=https://web.archive.org/web/20070221085835/http://www.gps.caltech.edu/classes/ge133/reading/asteroids.pdf |archive-date=21 February 2007 |access-date=22 March 2007}}</ref> The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometer in diameter.<ref>{{Cite journal |last1=Tedesco |first1=Edward F. |last2=Cellino |first2=Alberto |last3=Zappalá |first3=Vincenzo |date=June 2005 |title=The Statistical Asteroid Model. I. The Main-Belt Population for Diameters Greater than 1 Kilometer |journal=The Astronomical Journal |language=en |volume=129 |issue=6 |pages=2869–2886 |bibcode=2005AJ....129.2869T |doi=10.1086/429734 |issn=0004-6256 |s2cid=119906696 |doi-access=free}}</ref> Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth.<ref name="Krasinsky2002">{{Cite journal |last1=Krasinsky |first1=G. A. |author-link=Georgij A. Krasinsky |last2=Pitjeva |first2=E. V. |author-link2=Elena V. Pitjeva |last3=Vasilyev |first3=M. V. |last4=Yagudina |first4=E. I. |date=July 2002 |title=Hidden Mass in the Asteroid Belt |journal=[[Icarus (journal)|Icarus]] |volume=158 |issue=1 |pages=98–105 |bibcode=2002Icar..158...98K |doi=10.1006/icar.2002.6837}}</ref> The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident.<ref>{{Cite web |date=14 April 2000 |title=Cassini Passes Through Asteroid Belt |url=https://solarsystem.nasa.gov/news/12195/cassini-passes-through-asteroid-belt |url-status=live |archive-url=https://web.archive.org/web/20210125180703/https://solarsystem.nasa.gov/news/12195/cassini-passes-through-asteroid-belt |archive-date=25 January 2021 |access-date=1 March 2021 |website=NASA}}</ref>
[[File:The Four Largest Asteroids.jpg|thumb|The four largest asteroids: [[Ceres (dwarf planet)|Ceres]], [[4 Vesta|Vesta]], [[2 Pallas|Pallas]], [[10 Hygiea|Hygiea]]. Only Ceres and Vesta have been visited by a spacecraft and thus have a detailed picture.]]
Below are the descriptions of the three largest bodies in the asteroid belt. They are all considered to be relatively intact [[protoplanet]]s, a precursor stage before becoming a fully-formed planet (see [[List of exceptional asteroids]]):<ref>{{Cite journal |last1=McCord |first1=Thomas B. |last2=McFadden |first2=Lucy A. |last3=Russell |first3=Christopher T. |last4=Sotin |first4=Christophe |last5=Thomas |first5=Peter C. |date=7 March 2006 |title=Ceres, Vesta, and Pallas: Protoplanets, Not Asteroids |url=https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006EO100002 |url-status=live |journal=Eos |volume=87 |page=105 |bibcode=2006EOSTr..87..105M |doi=10.1029/2006EO100002 |archive-url=https://web.archive.org/web/20210928160233/https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006EO100002 |archive-date=28 September 2021 |access-date=12 September 2021 |number=10}}</ref><ref name="nasa-dawn20110329">{{cite web |author=Cook, Jia-Rui C. |date=29 March 2011 |title=When Is an Asteroid Not an Asteroid? |url=http://www.nasa.gov/mission_pages/dawn/news/dawn20110329.html |url-status=live |archive-url=https://web.archive.org/web/20110629163004/http://www.nasa.gov/mission_pages/dawn/news/dawn20110329.html |archive-date=29 June 2011 <!--DASHBot--> |access-date=30 July 2011 |publisher=NASA/JPL}}</ref><ref name="Marsset2020">{{Cite journal |last1=Marsset |first1=M. |last2=Brož |first2=M. |last3=Vernazza |first3=P. |last4=Drouard |first4=A. |display-authors=3 |date=2020 |title=The violent collisional history of aqueously evolved (2) Pallas |url=https://orbi.uliege.be/bitstream/2268/246670/1/Pallas_Marsset.pdf |journal=Nature Astronomy |volume=4 |issue=6 |pages=569–576 |bibcode=2020NatAs...4..569M |doi=10.1038/s41550-019-1007-5 |s2cid=212927521 |hdl-access=free |hdl=10261/237549 |access-date=4 January 2023 |archive-date=7 January 2023 |archive-url=https://web.archive.org/web/20230107085352/https://orbi.uliege.be/bitstream/2268/246670/1/Pallas_Marsset.pdf |url-status=live }}</ref>

* {{Visible anchor|Ceres|text=[[Ceres (dwarf planet)|Ceres]]}} (2.55–2.98&nbsp;AU) is the only dwarf planet in the asteroid belt.<ref name="IAU-QA">{{Cite web |title=Question and answers 2 |url=https://www.iau.org/public/themes/pluto/ |url-status=live |archive-url=https://web.archive.org/web/20160130022141/http://www.iau.org/public/themes/pluto/ |archive-date=30 January 2016 |access-date=31 January 2008 |publisher=IAU |quote=Ceres is (or now we can say it was) the largest asteroid{{spaces}}... There are many other asteroids that can come close to the orbital path of Ceres.}}</ref> It is the largest object in the belt, with a diameter of {{Convert|940|km|abbr=on}}.<ref name="Ermakov2017">{{cite journal |last1=Ermakov |first1=A. I. |last2=Fu |first2=R. R. |last3=Castillo-Rogez |first3=J. C. |last4=Raymond |first4=C. A. |last5=Park |first5=R. S. |last6=Preusker |first6=F. |last7=Russell |first7=C. T. |last8=Smith |first8=D. E. |last9=Zuber |first9=M. T. |date=November 2017 |title=Constraints on Ceres' Internal Structure and Evolution From Its Shape and Gravity Measured by the Dawn Spacecraft |journal=Journal of Geophysical Research: Planets |volume=122 |issue=11 |pages=2267–2293 |bibcode=2017JGRE..122.2267E |doi=10.1002/2017JE005302 |s2cid=133739176 |doi-access=free}}</ref> Its surface contains a mixture of [[carbon]],<ref name="Nature 12 2018">{{Cite journal |last1=Marchi |first1=S. |last2=Raponi |first2=A. |last3=Prettyman |first3=T. H. |last4=De Sanctis |first4=M. C. |last5=Castillo-Rogez |first5=J. |last6=Raymond |first6=C. A. |last7=Ammannito |first7=E. |last8=Bowling |first8=T. |last9=Ciarniello |first9=M. |last10=Kaplan |first10=H. |last11=Palomba |first11=E. |last12=Russell |first12=C. T. |last13=Vinogradoff |first13=V. |last14=Yamashita |first14=N. |year=2018 |title=An aqueously altered carbon-rich Ceres |journal=[[Nature Astronomy]] |volume=3 |issue=2 |pages=140–145 |doi=10.1038/s41550-018-0656-0 |s2cid=135013590}}</ref> frozen water and [[hydrate]]d minerals.<ref name="EPSC2">{{Cite book |last1=Raymond |first1=C. |title=European Planetary Science Congress |last2=Castillo-Rogez |first2=J. C. |last3=Park |first3=R. S. |last4=Ermakov |first4=A. |last5=Bland |first5=M. T. |last6=Marchi |first6=S. |last7=Prettyman |first7=T. |last8=Ammannito |first8=E. |last9=De Sanctis |first9=M. C. |date=September 2018 |volume=12 |chapter=Dawn Data Reveal Ceres' Complex Crustal Evolution |display-authors=4 |access-date=19 July 2020 |chapter-url=https://meetingorganizer.copernicus.org/EPSC2018/EPSC2018-645-1.pdf |archive-url=https://web.archive.org/web/20200130111631/https://meetingorganizer.copernicus.org/EPSC2018/EPSC2018-645-1.pdf |archive-date=30 January 2020 |url-status=live |author10=Russell, C.T.}}</ref> There are signs of past [[cryovolcano|cryovolcanic]] activity, where [[volatile (astrogeology)|volatile]] material such as water are erupted onto the surface, as seen in [[Bright spots on Ceres|surface bright spots]].<ref>{{cite web |last1=Krummheuer |first1=Birgit |date=6 March 2017 |title=Cryovolcanism on Dwarf Planet Ceres |url=http://www.mps.mpg.de/Cryovolcanism-on-Dwarf-Planet-Ceres |website=Max Planck Institute for Solar System Research |access-date=22 April 2024 |archive-date=2 February 2024 |archive-url=https://web.archive.org/web/20240202180118/https://www.mps.mpg.de/Cryovolcanism-on-Dwarf-Planet-Ceres |url-status=live }}</ref> Ceres has a very thin water vapor atmosphere, but practically speaking it is indistinguishable from a vacuum.<ref>{{Cite news |date=6 April 2017 |title=Confirmed: Ceres Has a Transient Atmosphere |url=https://www.universetoday.com/134922/confirmed-ceres-transient-atmosphere/ |url-status=live |archive-url=https://web.archive.org/web/20170415103956/https://www.universetoday.com/134922/confirmed-ceres-transient-atmosphere/ |archive-date=15 April 2017 |access-date=14 April 2017 |work=Universe Today |language=en}}</ref>
* {{Visible anchor|Pallas and Vesta|text=[[4 Vesta|Vesta]]}} (2.13–3.41&nbsp;AU) is the second-largest object in the asteroid belt.<ref name="Astronomy & Astrophysics">{{Cite report |url=https://meetingorganizer.copernicus.org/EPSC2022/EPSC2022-103.html |title=VLT/SPHERE imaging survey of D>100 km asteroids: Final results and synthesis |last1=Vernazza |first1=Pierre |last2=Ferrais |first2=Marin |date=6 July 2022 |publisher=Astronomy & Astrophysics |doi=10.5194/epsc2022-103 |page=A56 |last3=Jorda |first3=Laurent |last4=Hanus |first4=Josef |last5=Carry |first5=Benoit |last6=Marsset |first6=Michael |last7=Brož |first7=Miroslav |last8=Fetick |first8=Roman |last9=HARISSA team |doi-access=free |access-date=22 April 2024 |archive-date=22 April 2024 |archive-url=https://web.archive.org/web/20240422145344/https://meetingorganizer.copernicus.org/EPSC2022/EPSC2022-103.html |url-status=live }}</ref> Its fragments survive as the [[Vesta family|Vesta asteroid family]]<ref name="planetarysociety" /> and numerous [[HED meteorite]]s found on Earth.<ref name="Vestainterior">{{cite web |date=6 January 2011 |title=A look into Vesta's interior |url=https://www.mpg.de/877913/Vesta_asteroid |work=Max-Planck-Gesellschaft |access-date=22 April 2024 |archive-date=5 March 2023 |archive-url=https://web.archive.org/web/20230305200352/https://www.mpg.de/877913/Vesta_asteroid |url-status=live }}</ref> Vesta's surface, dominated by [[basalt]]ic and [[Metamorphic rock|metamorphic]] material, has a denser composition than Ceres's.<ref name="Takeda1997">{{cite journal |author=Takeda, H. |date=1997 |title=Mineralogical records of early planetary processes on the HED parent body with reference to Vesta |journal=Meteoritics & Planetary Science |volume=32 |issue=6 |pages=841–853 |bibcode=1997M&PS...32..841T |doi=10.1111/j.1945-5100.1997.tb01574.x |doi-access=free}}</ref> Its surface is marked by two giant craters: [[Rheasilvia]] and [[Veneneia (crater)|Veneneia]].<ref name="Schenk2012">{{cite journal |author=Schenk, P. |display-authors=etal |date=2012 |title=The Geologically Recent Giant Impact Basins at Vesta's South Pole |journal=Science |volume=336 |issue=6082 |pages=694–697 |bibcode=2012Sci...336..694S |doi=10.1126/science.1223272 |pmid=22582256 |s2cid=206541950}}</ref>
* [[2 Pallas|Pallas]] (2.15–2.57&nbsp;AU) is the third-largest object in the asteroid belt.<ref name="Astronomy & Astrophysics"/> It has its own [[Pallas family|Pallas]] [[Vesta family|asteroid family]].<ref name="planetarysociety">{{Cite web |last=Lakdawalla |first=Emily |author-link=Emily Lakdawalla |display-authors=etal |date=21 April 2020 |title=What Is A Planet? |url=https://www.planetary.org/worlds/what-is-a-planet |url-status=live |archive-url=https://web.archive.org/web/20220122142140/https://www.planetary.org/worlds/what-is-a-planet |archive-date=22 January 2022 |access-date=3 April 2022 |website=The Planetary Society}}</ref> Not much is known about Pallas because it has never been visited by a spacecraft,<ref>{{cite web |title=Athena: A SmallSat Mission to (2) Pallas |url=https://josephgorourke.com/research |url-status=dead |archive-url=https://web.archive.org/web/20211121181742/https://josephgorourke.com/research |archive-date=21 November 2021 |access-date=7 October 2020}}</ref> though its surface is predicted to be composed of silicates.<ref name="AutoCB-19">{{cite journal |author=Feierberg, M. A. |author2=Larson, H. P. |author3=Lebofsky, L. A. |date=1982 |title=The 3 Micron Spectrum of Asteroid 2 Pallas |journal=Bulletin of the American Astronomical Society |volume=14 |page=719 |bibcode=1982BAAS...14..719F}}</ref>

[[Hilda asteroid]]s are in a 3:2 resonance with Jupiter; that is, they go around the Sun three times for every two Jovian orbits.<ref name="Barucci">{{Cite book |last1=Barucci |first1=M. A. |title=Asteroids III |last2=Kruikshank |first2=D. P. |last3=Mottola |first3=S. |last4=Lazzarin |first4=M. |date=2002 |publisher=University of Arizona Press |location=Tucson, Arizona |pages=273–287 |chapter=Physical Properties of Trojan and Centaur Asteroids}}</ref> They lie in three linked clusters between Jupiter and the main asteroid belt.

[[Trojan (celestial body)|Trojan]]s are bodies located within another body's gravitationally stable [[Lagrangian point|Lagrange points]]: {{L4}}, 60° ahead in its orbit, or {{L5}}, 60° behind in its orbit.<ref name="spies">{{cite web |title=Trojan Asteroids |url=http://astronomy.swin.edu.au/cosmos/T/Trojan+Asteroids |url-status=live |archive-url=https://web.archive.org/web/20170623182748/http://astronomy.swin.edu.au/cosmos/T/Trojan+Asteroids |archive-date=23 June 2017 |access-date=13 June 2017 |website=Cosmos |publisher=Swinburne University of Technology}}</ref> Every planet except Mercury and Saturn is known to possess at least 1 trojan.<ref name="Connors">{{cite journal |last1= Connors|first1= Martin|last2= Wiegert|first2= Paul|last3= Veillet|first3= Christian|title= Earth's Trojan asteroid|date= 27 July 2011|journal= [[Nature (journal)|Nature]]|volume= 475|pages= 481–483|doi= 10.1038/nature10233|issue= 7357|bibcode= 2011Natur.475..481C|pmid= 21796207|s2cid= 205225571}}</ref><ref name=secondUranus>{{cite journal
|last2=de la Fuente Marcos |first2=Raúl
|last1=de la Fuente Marcos |first1=Carlos
|title=Asteroid 2014 YX<sub>49</sub>: a large transient Trojan of Uranus
|journal=Monthly Notices of the Royal Astronomical Society
|date=21 May 2017
|volume=467 |issue=2
|arxiv=1701.05541
|doi=10.1093/mnras/stx197 |pages=1561–1568|doi-access=free
|bibcode=2017MNRAS.467.1561D}}</ref><ref name=CeresVestatrojans>{{cite journal |first1=Apostolos A. |last1=Christou |first2=Paul |last2=Wiegert |title=A population of main belt asteroids co-orbiting with Ceres and Vesta |journal=Icarus |volume=217 |issue=1 |date=January 2012 |pages=27–42 |arxiv=1110.4810 |doi=10.1016/j.icarus.2011.10.016|bibcode=2012Icar..217...27C |s2cid=59474402 }}</ref> The [[Jupiter trojan]] population is roughly equal to that of the asteroid belt.<ref name="Yoshida2005">{{cite journal |last1=Yoshida |first1=Fumi |last2=Nakamura |first2=Tsuko |title=Size distribution of faint L4 Trojan asteroids |year=2005 |journal=The Astronomical Journal |volume=130 |issue=6 |pages=2900–11 |doi=10.1086/497571 |bibcode=2005AJ....130.2900Y|doi-access=free }}</ref> After Jupiter, Neptune possesses the most confirmed trojans, at 28.<ref>{{cite web |title=List of Neptune Trojans |work=Minor Planet Center |date=28 October 2018 |access-date=28 December 2018 |url=http://www.minorplanetcenter.org/iau/lists/NeptuneTrojans.html |archive-date=25 May 2012 |archive-url=https://archive.today/20120525133119/http://www.minorplanetcenter.org/iau/lists/NeptuneTrojans.html |url-status=live }}</ref>

== Outer Solar System ==
The outer region of the Solar System is home to the [[giant planet]]s and their large moons. The [[Centaur (minor planet)|centaurs]] and many [[short-period comet]]s orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles such as water, ammonia, and methane, than planets of the inner Solar System because their lower temperatures allow these compounds to remain solid, without significant [[Sublimation (phase transition)|sublimation]].<ref name="bennett_8.2"/>

=== Outer planets ===
{{Main|Giant planet}}
[[File:Planet collage to scale (captioned).jpg|right|thumb|alt=Jupiter and Saturn is about 2 times bigger than Uranus and Neptune, 10 times bigger than Venus and Earth, 20 times bigger than Mars and 25 times bigger than Mercury|The outer planets [[Jupiter]], [[Saturn]], [[Uranus]] and [[Neptune]], compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right]]
The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun.<ref group="lower-alpha" name="footnoteD" /> All four giant planets have multiple moons and a ring system, although only Saturn's rings are easily observed from Earth.<ref name="Ryden" /> Jupiter and Saturn are composed mainly of gases with extremely low melting points, such as hydrogen, helium, and [[neon]],<ref name="Podolak Podolak et al. 2000">{{Cite journal |last1=Podolak |first1=M. |last2=Podolak |first2=J. I. |last3=Marley |first3=M. S. |date=February 2000 |title=Further investigations of random models of Uranus and Neptune |url=https://zenodo.org/record/998024 |url-status=live |journal=Planetary and Space Science |volume=48 |issue=2–3 |pages=143–151 |bibcode=2000P&SS...48..143P |doi=10.1016/S0032-0633(99)00088-4 |archive-url=https://web.archive.org/web/20191221231229/https://zenodo.org/record/998024 |archive-date=21 December 2019 |access-date=25 August 2019 |ref={{SfnRef|Podolak Podolak et al.|2000}}}}</ref> hence their designation as [[gas giant]]s.<ref>{{Cite web |title=Gas Giant {{!}} Planet Types |url=https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/gas-giant |url-status=live |archive-url=https://web.archive.org/web/20201128232046/https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/gas-giant |archive-date=28 November 2020 |access-date=22 December 2020 |website=Exoplanet Exploration: Planets Beyond our Solar System}}</ref> Uranus and Neptune are [[ice giants]],<ref>{{Cite web |last1=Lissauer |first1=Jack J. |last2=Stevenson |first2=David J. |date=2006 |title=Formation of Giant Planets |url=http://www.gps.caltech.edu/uploads/File/People/djs/lissauer&stevenson(PPV).pdf |url-status=dead |archive-url=https://web.archive.org/web/20090326060004/http://www.gps.caltech.edu/uploads/File/People/djs/lissauer%26stevenson%28PPV%29.pdf |archive-date=26 March 2009 |access-date=16 January 2006 |website=NASA Ames Research Center; California Institute of Technology}}</ref> meaning they are largely composed of [[Volatile (astrogeology)|'ice' in the astronomical sense]] (chemical compounds with melting points of up to a few hundred [[kelvin]]s<ref name="Podolak Podolak et al. 2000" /> such as water, methane, ammonia, [[hydrogen sulfide]], and [[carbon dioxide]].<ref name="Podolak Weizman et al. 1995">{{Cite journal |last1=Podolak |first1=M. |last2=Weizman |first2=A. |last3=Marley |first3=M. |date=December 1995 |title=Comparative models of Uranus and Neptune |journal=Planetary and Space Science |volume=43 |issue=12 |pages=1517–1522 |bibcode=1995P&SS...43.1517P |doi=10.1016/0032-0633(95)00061-5 |ref={{SfnRef|Podolak Weizman et al.|1995}}}}</ref>) Icy substances comprise the majority of the satellites of the giant planets and small objects that lie beyond Neptune's orbit.<ref name="Podolak Weizman et al. 1995" /><ref name="zeilik">{{Cite book |last=Zellik |first=Michael |title=Astronomy: The Evolving Universe |date=2002 |publisher=[[Cambridge University Press]] |isbn=978-0-521-80090-7 |edition=9th |page=240 |oclc=223304585}}</ref>

* {{Visible anchor|Jupiter|text=[[Jupiter]]}} (4.95–5.46&nbsp;AU)<ref name="nasa-factsheet" group="D" /> is the biggest and most massive planet in the Solar System. On its surface, there are orange-brown and white cloud bands moving via the principles of [[atmospheric circulation]], with giant storms swirling on the surface such as the [[Great Red Spot]] and [[Oval BA|white 'ovals']]. [[Magnetosphere of Jupiter|Jupiter possesses a strong enough magnetosphere]] to redirect [[ionizing radiation]] and cause [[aurora]]s on its poles.<ref>{{Cite book |last=Rogers |first=John H. |url=https://books.google.com/books?id=SO48AAAAIAAJ&pg=PA293 |title=The giant planet Jupiter |date=1995 |publisher=Cambridge University Press |isbn=978-0521410083 |page=293 |access-date=13 April 2022 |archive-url=https://web.archive.org/web/20220420161219/https://www.google.com/books/edition/The_Giant_Planet_Jupiter/SO48AAAAIAAJ?gbpv=1&pg=PA293 |archive-date=20 April 2022 |url-status=live}}</ref> As of 2024, Jupiter has [[Moons of Jupiter|95 confirmed satellites]], which can roughly be sorted into three groups:
** The Amalthea group, consisting of [[Metis (moon)|Metis]], [[Adrastea (moon)|Adrastea]], [[Amalthea (moon)|Amalthea]], and [[Thebe (moon)|Thebe]]. They orbit substantially closer to Jupiter than other satellites.<ref>{{cite journal |last=Anderson |first=J.D. |author2=Johnson, T.V. |author3=Shubert, G. |display-authors=etal |date=2005 |title=Amalthea's Density Is Less Than That of Water |journal=Science |volume=308 |issue=5726 |pages=1291–1293 |bibcode=2005Sci...308.1291A |doi=10.1126/science.1110422 |pmid=15919987 |s2cid=924257}}</ref> Materials from these natural satellites are the source of Jupiter's faint ring.<ref>{{cite journal |author=Burns, J. A. |author2=Showalter, M. R. |author3=Hamilton, D. P. |display-authors=etal |date=1999 |title=The Formation of Jupiter's Faint Rings |journal=Science |volume=284 |issue=5417 |pages=1146–1150 |bibcode=1999Sci...284.1146B |doi=10.1126/science.284.5417.1146 |pmid=10325220 |s2cid=21272762}}</ref>
** The [[Galilean moons]], consisting of [[Ganymede (moon)|Ganymede]], [[Callisto (moon)|Callisto]], [[Io (moon)|Io]], and [[Europa (moon)|Europa]]. They are the largest moons of Jupiter and exhibit planetary properties.<ref>{{Cite web |last=Pappalardo |first=R. T. |date=1999 |title=Geology of the Icy Galilean Satellites: A Framework for Compositional Studies |url=http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm99&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm99%2Ffm99&maxhits=200&=%22P11C-10%22 |url-status=dead |archive-url=https://web.archive.org/web/20070930165551/http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm99&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm99%2Ffm99&maxhits=200&=%22P11C-10%22 |archive-date=30 September 2007 |access-date=16 January 2006 |website=Brown University}}</ref>
** Irregular satellites, consisting of substantially smaller natural satellites. They have more distant orbits than the other objects.<ref name="list">{{cite book |author=Sheppard, Scott S. |title=Jupiter. The planet, satellites and magnetosphere |author2=Jewitt, David C. |author3=Porco, Carolyn |date=2004 |publisher=Cambridge University Press |isbn=0-521-81808-7 |editor=Fran Bagenal |volume=1 |location=Cambridge, UK |pages=263–280 |chapter=Jupiter's outer satellites and Trojans |editor2=Timothy E. Dowling |editor3=William B. McKinnon |chapter-url=http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-url=https://web.archive.org/web/20090326065151/http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-date=26 March 2009 |url-status=dead}}</ref>
* {{Visible anchor|Saturn|text=[[Saturn]]}} (9.08–10.12&nbsp;AU)<ref name="nasa-factsheet" group="D" /> has a distinctive visible [[Rings of Saturn|ring system]] orbiting around its equator composed of small ice and rock particles. Like Jupiter, it is mostly made of hydrogen and helium.<ref>{{Cite web |date=18 August 2021 |title=In Depth: Saturn |url=https://solarsystem.nasa.gov/planets/saturn/in-depth |url-status=live |archive-url=https://web.archive.org/web/20180224210031/https://solarsystem.nasa.gov/planets/saturn/in-depth |archive-date=24 February 2018 |access-date=31 March 2022 |website=NASA Science: Solar System Exploration}}</ref> At its north and south poles, Saturn has peculiar [[Saturn's hexagon|hexagon-shaped storms]] larger than the diameter of Earth. [[Magnetosphere of Saturn|Saturn has a magnetosphere]] capable of producing weak auroras. As of 2024, Saturn has [[Moons of Saturn|146 confirmed satellites]], grouped into:
** Ring [[moonlet]]s and [[Shepherd moon|shepherds]], which orbit inside or close to Saturn's rings. A moonlet can only partially clear out dust in its orbit,<ref name="Sremcevic2007">{{cite journal |last1=Sremčević |first1=Miodrag |last2=Schmidt |first2=Jürgen |last3=Salo |first3=Heikki |last4=Seiß |first4=Martin |last5=Spahn |first5=Frank |last6=Albers |first6=Nicole |date=2007 |title=A belt of moonlets in Saturn's A ring |journal=[[Nature (journal)|Nature]] |volume=449 |issue=7165 |pages=1019–21 |bibcode=2007Natur.449.1019S |doi=10.1038/nature06224 |pmid=17960236 |s2cid=4330204}}</ref> while the ring shepherds are able to completely clear out dust, forming visible gaps in the rings.<ref name="Porco2005">{{cite journal |last1=Porco |first1=C. C. |last2=Baker |first2=E. |last3=Barbara |first3=J. |display-authors=etal |date=2005 |title=Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites |url=http://ciclops.org/sci/docs/RingsSatsPaper.pdf |journal=Science |volume=307 |issue=5713 |pages=1234 |bibcode=2005Sci...307.1226P |doi=10.1126/science.1108056 |pmid=15731439 |s2cid=1058405 |access-date=21 April 2024 |archive-date=25 July 2011 |archive-url=https://web.archive.org/web/20110725171940/http://ciclops.org/sci/docs/RingsSatsPaper.pdf |url-status=live }}</ref>
** Inner large satellites [[Mimas]], [[Enceladus]], [[Tethys (moon)|Tethys]], and [[Dione (moon)|Dione]]. These satellites orbit within [[Rings of Saturn#E Ring|Saturn's E ring]]. They are composed mostly of water ice and are believed to have differentiated internal structures.<ref name=":2">{{Cite web |last=Williams |first=Matt |date=7 August 2015 |title=The moons of Saturn |url=https://phys.org/news/2015-08-moons-saturn.html |access-date=21 April 2024 |website=phys.org |language=en |archive-date=21 April 2024 |archive-url=https://web.archive.org/web/20240421075712/https://phys.org/news/2015-08-moons-saturn.html |url-status=live }}</ref>
** Trojan moons [[Calypso (moon)|Calypso]] and [[Telesto (moon)|Telesto]] (trojans of Tethys), and [[Helene (moon)|Helene]] and [[Polydeuces (moon)|Polydeuces]] (trojans of Dione). These small moons share their orbits with Tethys and Dione, leading or trailing either.<ref name="Calypso">{{cite web |publisher=NASA |url=https://science.nasa.gov/saturn/moons/calypso/ |title=Calypso |date=January 2024 |access-date=16 May 2024 |archive-date=17 May 2024 |archive-url=https://web.archive.org/web/20240517022857/https://science.nasa.gov/saturn/moons/calypso/ |url-status=live }}</ref><ref name="Polydeuces">{{cite web |publisher=NASA |url=https://science.nasa.gov/saturn/moons/polydeuces/ |title=Polydeuces |date=January 2024 |access-date=16 May 2024 }}</ref>
** Outer large satellites [[Rhea (moon)|Rhea]], [[Titan (moon)|Titan]], [[Hyperion (moon)|Hyperion]], and [[Iapetus (moon)|Iapetus]].<ref name=":2" /> Titan is the only satellite in the Solar System to have a substantial atmosphere.<ref name="Forget2017">{{cite journal |last1=Forget |first1=F. |last2=Bertrand |first2=T. |last3=Vangvichith |first3=M. |last4=Leconte |first4=J. |last5=Millour |first5=E. |last6=Lellouch |first6=E. |title=A post-New Horizons Global climate model of Pluto including the N 2, CH 4 and CO cycles |date=May 2017 |journal=Icarus |volume=287 |pages=54–71 |doi=10.1016/j.icarus.2016.11.038 |bibcode=2017Icar..287...54F|url=https://hal.sorbonne-universite.fr/hal-01427123/file/Forget_A_post-New_Horizons.pdf }}</ref>
** Irregular satellites, consisting of substantially smaller natural satellites. They have more distant orbits than the other objects. [[Phoebe (moon)|Phoebe]] is the largest irregular satellite of Saturn.<ref name="Jewitt2007"/>
* {{Visible anchor|Uranus|text=[[Uranus]]}} (18.3–20.1&nbsp;AU),<ref name="nasa-factsheet" group="D" /> uniquely among the planets, orbits the Sun on its side with an [[axial tilt]] >90°. This gives the planet extreme seasonal variation as each pole points alternately toward and then away from the Sun.<ref>{{Cite web |last=Devitt |first=Terry |date=14 October 2008 |title=New images yield clues to seasons of Uranus |publisher=University of Wisconsin–Madison |url=https://news.wisc.edu/new-images-yield-clues-to-seasons-of-uranus/ |access-date=6 April 2024 |archive-date=6 April 2024 |archive-url=https://web.archive.org/web/20240406210615/https://news.wisc.edu/new-images-yield-clues-to-seasons-of-uranus/ |url-status=live }}</ref> Uranus' outer layer has a muted [[cyan]] color, but underneath these clouds are [[Climate of Uranus|many mysteries about its climate]], such as unusually low [[internal heat]] and erratic cloud formation. As of 2024, Uranus has [[Moons of Uranus|28 confirmed satellites]], divided into three groups:
** Inner satellites, which orbit inside Uranus' ring system.<ref name="Esposito2002">{{cite journal |last=Esposito |first=L. W. |author-link=Larry W. Esposito |year=2002 |title=Planetary rings |journal=Reports on Progress in Physics |volume=65 |issue=12 |pages=1741–1783 |bibcode=2002RPPh...65.1741E |doi=10.1088/0034-4885/65/12/201 |s2cid=250909885}}</ref> They are very close to each other, which suggests that their orbits are [[Chaotic system|chaotic]].<ref name="Duncan Lissauer 1997">{{cite journal |last1=Duncan |first1=Martin J. |last2=Lissauer |first2=Jack J. |year=1997 |title=Orbital Stability of the Uranian Satellite System |journal=Icarus |volume=125 |issue=1 |pages=1–12 |bibcode=1997Icar..125....1D |doi=10.1006/icar.1996.5568}}</ref>
** Large satellites, consisting of [[Titania (moon)|Titania]], [[Oberon (moon)|Oberon]], [[Umbriel]], [[Ariel (moon)|Ariel]], and [[Miranda (moon)|Miranda]].<ref>{{Cite journal |last1=Sheppard |first1=S. S. |last2=Jewitt |first2=D. |last3=Kleyna |first3=J. |year=2005 |title=An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness |journal=The Astronomical Journal |volume=129 |issue=1 |page=518 |arxiv=astro-ph/0410059 |bibcode=2005AJ....129..518S |doi=10.1086/426329 |s2cid=18688556}}</ref> Most of them have roughly equal amounts of rock and ice, except Miranda, which is made primarily of ice.<ref name="Hussmann Sohl et al. 2006">{{cite journal |last1=Hussmann |first1=Hauke |last2=Sohl |first2=Frank |last3=Spohn |first3=Tilman |date=November 2006 |title=Subsurface oceans and deep interiors of medium-sized outer planet satellites and large trans-neptunian objects |journal=[[Icarus (journal)|Icarus]] |volume=185 |issue=1 |pages=258–273 |bibcode=2006Icar..185..258H |doi=10.1016/j.icarus.2006.06.005 |ref={{sfnRef|Hussmann Sohl et al.|2006}}}}</ref>
** Irregular satellites, having more distant and eccentric orbits than the other objects.<ref name="Sheppardmoons2024">{{cite web |date=23 February 2024 |title=New Uranus and Neptune Moons |url=https://sites.google.com/carnegiescience.edu/sheppard/home/newuranusneptunemoons |accessdate=23 February 2024 |work=Earth & Planetary Laboratory |publisher=Carnegie Institution for Science |archive-date=23 February 2024 |archive-url=https://web.archive.org/web/20240223160326/https://sites.google.com/carnegiescience.edu/sheppard/home/newuranusneptunemoons |url-status=live }}</ref>
* {{Visible anchor|Neptune|text=[[Neptune]]}} (29.9–30.5&nbsp;AU)<ref name="nasa-factsheet" group="D" /> is the furthest planet known in the Solar System. Its outer atmosphere has a slightly muted cyan color, with occasional storms on the surface that look like dark spots. Like Uranus, many atmospheric phenomena of Neptune are unexplained, such as the [[thermosphere]]'s abnormally high temperature or the strong tilt (47°) of its magnetosphere. As of 2024, Neptune has [[Moons of Neptune|16 confirmed satellites]], divided into two groups:
** Regular satellites, which have circular orbits that lie near Neptune's equator.<ref name="Jewitt2007">{{cite journal |last=Jewitt |first=David |author2=Haghighipour, Nader |date=2007 |title=Irregular Satellites of the Planets: Products of Capture in the Early Solar System |url=http://www2.ess.ucla.edu/~jewitt/papers/2007/JH07.pdf |journal=Annual Review of Astronomy and Astrophysics |volume=45 |issue=1 |pages=261–95 |arxiv=astro-ph/0703059 |bibcode=2007ARA&A..45..261J |doi=10.1146/annurev.astro.44.051905.092459 |s2cid=13282788 |access-date=21 April 2024 |archive-date=25 February 2014 |archive-url=https://web.archive.org/web/20140225204338/http://www2.ess.ucla.edu/~jewitt/papers/2007/JH07.pdf |url-status=live }}</ref>
** Irregular satellites, which as the name implies, have less regular orbits. One of them, [[Triton (moon)|Triton]], is Neptune's largest moon. It is geologically active, with erupting [[geyser]]s of nitrogen gas, and possesses a thin, cloudy nitrogen atmosphere.<ref name="Soderblom2">{{Cite journal |last1=Soderblom |first1=L. A. |last2=Kieffer |first2=S. W. |last3=Becker |first3=T. L. |last4=Brown |first4=R. H. |last5=Cook |first5=A. F. II |last6=Hansen |first6=C. J. |last7=Johnson |first7=T. V. |last8=Kirk |first8=R. L. |last9=Shoemaker |first9=E. M. |author-link9=Eugene Merle Shoemaker |date=19 October 1990 |title=Triton's Geyser-Like Plumes: Discovery and Basic Characterization |url=https://www.geology.illinois.edu/~skieffer/papers/Truiton_Science_1990.pdf |url-status=live |journal=[[Science (journal)|Science]] |volume=250 |issue=4979 |pages=410–415 |bibcode=1990Sci...250..410S |doi=10.1126/science.250.4979.410 |pmid=17793016 |s2cid=1948948 |archive-url=https://web.archive.org/web/20210831121844/https://geology.illinois.edu/~skieffer/papers/Truiton_Science_1990.pdf |archive-date=31 August 2021 |access-date=31 March 2022}}</ref><ref name="Forget2017"/>

=== {{Anchor|Centaurs}}Centaurs ===
{{Main|Centaur (small Solar System body)|l1 = Centaur}}

The centaurs are icy, comet-like bodies whose [[Semi-major and semi-minor axes|semi-major axes]] are longer than Jupiter's and shorter than Neptune's (between 5.5 and 30&nbsp;AU). These are former Kuiper belt and [[Scattered disc|scattered disc objects]] (SDOs) that were gravitationally [[perturbation (astronomy)|perturbed]] closer to the Sun by the outer planets, and are expected to become comets or be ejected out of the Solar System.<ref name="Delsanti-Beyond_The_Planets" /> While most centaurs are inactive and asteroid-like, some exhibit cometary activity, such as the first centaur discovered, [[2060 Chiron]], which has been classified as a comet (95P) because it develops a coma just as comets do when they approach the Sun.<ref>{{Cite web |last=Vanouplines |first=Patrick |date=1995 |title=Chiron biography |url=http://www.vub.ac.be/STER/www.astro/chibio.htm |url-status=dead |archive-url=https://web.archive.org/web/20090502122306/http://www.vub.ac.be/STER/www.astro/chibio.htm |archive-date=2 May 2009 |access-date=23 June 2006 |website=Vrije Universitiet Brussel}}</ref> The largest known centaur, [[10199 Chariklo]], has a diameter of about {{Convert|250|km|abbr=on}} and is one of the few minor planets possessing a ring system.<ref name="spitzer">{{Cite conference |last1=Stansberry |first1=John |last2=Grundy |first2=Will |last3=Brown |first3=Mike |last4=Cruikshank |first4=Dale |last5=Spencer |first5=John |last6=Trilling |first6=David |last7=Margot |first7=Jean-Luc |date=2007 |title=Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope |page=161 |arxiv=astro-ph/0702538 |bibcode=2008ssbn.book..161S |book-title=The Solar System Beyond Neptune}}</ref><ref name="Braga-Ribas-2014">{{Cite journal |last=Braga-Ribas |first=F. |display-authors=etal |date=April 2014 |title=A ring system detected around the Centaur (10199) Chariklo |journal=[[Nature (journal)|Nature]] |volume=508 |issue=7494 |pages=72–75 |arxiv=1409.7259 |bibcode=2014Natur.508...72B |doi=10.1038/nature13155 |issn=0028-0836 |pmid=24670644 |s2cid=4467484}}</ref>

== Trans-Neptunian region ==
Beyond the orbit of Neptune lies the area of the "[[trans-Neptunian object|trans-Neptunian region]]", with the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets, and an overlapping disc of scattered objects, which is [[Orbital inclination|tilted toward the plane]] of the Solar System and reaches much further out than the Kuiper belt. The entire region is still [[Timeline of Solar System exploration|largely unexplored]]. It appears to consist overwhelmingly of many thousands of small worlds—the largest having a diameter only a fifth that of Earth and a mass far smaller than that of the Moon—composed mainly of rock and ice. This region is sometimes described as the "third zone of the Solar System", enclosing the inner and the outer Solar System.<ref>{{Cite web |last=Stern |first=Alan |author-link=Alan Stern |date=February 2015 |title=Journey to the Solar System's Third Zone |url=https://www.americanscientist.org/article/journey-to-the-solar-systems-third-zone |url-status=live |archive-url=https://web.archive.org/web/20181026222414/https://www.americanscientist.org/article/journey-to-the-solar-systems-third-zone |archive-date=26 October 2018 |access-date=26 October 2018 |website=American Scientist}}</ref>

=== Kuiper belt ===
{{Main|Kuiper belt}}
[[File:Kuiper belt plot objects of outer solar system.png|right|thumb|Plot of objects around the [[Kuiper belt]] and other asteroid populations. J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune.]]

[[File:TheKuiperBelt_classes-en.svg|thumb|Orbit classification of Kuiper belt objects. Some clusters that is subjected to [[orbital resonance]] are marked.]]
The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice.<ref name="physical">{{Cite book |last=Tegler |first=Stephen C. |url=https://archive.org/details/encyclopediasola00mcfa_702 |title=Encyclopedia of the Solar System |date=2007 |isbn=978-0120885893 |editor-last=Lucy-Ann McFadden |page=[https://archive.org/details/encyclopediasola00mcfa_702/page/n622 605]–620 |chapter=Kuiper Belt Objects: Physical Studies |display-editors=etal |url-access=limited}}</ref> It extends between 30 and 50&nbsp;AU from the Sun. It is composed mainly of small Solar System bodies, although the largest few are probably large enough to be dwarf planets.<ref name="Grundy2019">{{Cite journal |last1=Grundy |first1=W. M. |last2=Noll |first2=K. S. |last3=Buie |first3=M. W. |last4=Benecchi |first4=S. D. |last5=Ragozzine |first5=D. |last6=Roe |first6=H. G. |date=December 2018 |title=The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ({{Mp|(229762) 2007 UK|126}}) |url=http://www2.lowell.edu/~grundy/abstracts/2019.G-G.html |volume=334 |pages=30–38 |doi=10.1016/j.icarus.2018.12.037 |s2cid=126574999 |archive-url=https://web.archive.org/web/20190407045339/http://www2.lowell.edu/~grundy/abstracts/preprints/2019.G-G.pdf |archive-date=7 April 2019 |journal=Icarus|bibcode=2019Icar..334...30G }}</ref> There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than {{Convert|50|km|abbr=on|sigfig=1}}, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth.<ref name="Delsanti-Beyond_The_Planets">{{Cite web |last1=Delsanti |first1=Audrey |last2=Jewitt |first2=David |date=2006 |title=The Solar System Beyond The Planets |url=http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070129151907/http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |archive-date=29 January 2007 |access-date=3 January 2007 |website=Institute for Astronomy, University of Hawaii}}</ref> Many Kuiper belt objects have satellites,<ref>{{Cite journal |last1=Brown |first1=M.E. |author-link=Michael E. Brown |last2=Van Dam |first2=M.A. |last3=Bouchez |first3=A.H. |last4=Le Mignant |first4=D. |last5=Campbell |first5=R.D. |last6=Chin |first6=J.C.Y. |last7=Conrad |first7=A. |last8=Hartman |first8=S.K. |last9=Johansson |first9=E.M. |last10=Lafon |first10=R.E. |last11=Rabinowitz |first11=D.L. Rabinowitz |last12=Stomski |first12=P.J. Jr. |last13=Summers |first13=D.M. |last14=Trujillo |first14=C.A. |last15=Wizinowich |first15=P.L. |year=2006 |title=Satellites of the Largest Kuiper Belt Objects |url=http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf |url-status=live |journal=[[The Astrophysical Journal]] |volume=639 |issue=1 |pages=L43–L46 |arxiv=astro-ph/0510029 |bibcode=2006ApJ...639L..43B |doi=10.1086/501524 |s2cid=2578831 |archive-url=https://web.archive.org/web/20180928185647/http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf |archive-date=28 September 2018 |access-date=19 October 2011 |ref={{SfnRef|Brown Van Dam et al.|2006}}}}</ref> and most have orbits that are substantially inclined (~10°) to the plane of the ecliptic.<ref name="trojan">{{Cite journal |last1=Chiang |first1=E.I. |last2=Jordan |first2=A.B. |last3=Millis |first3=R.L. |last4=Buie |first4=M.W. |last5=Wasserman |first5=L.H. |last6=Elliot |first6=J.L. |last7=Kern |first7=S.D. |last8=Trilling |first8=D.E. |last9=Meech |first9=K.J. |last10=Wagner |first10=R.M. |display-authors=9 |date=2003 |title=Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances |url=http://www.boulder.swri.edu/~buie/biblio/pub047.pdf |url-status=live |journal=[[The Astronomical Journal]] |volume=126 |issue=1 |pages=430–443 |arxiv=astro-ph/0301458 |bibcode=2003AJ....126..430C |doi=10.1086/375207 |s2cid=54079935 |archive-url=https://web.archive.org/web/20160315175243/http://www.boulder.swri.edu//~buie/biblio/pub047.pdf |archive-date=15 March 2016 |access-date=15 August 2009}}</ref>

The Kuiper belt can be roughly divided into the "[[Classical Kuiper belt object|classical]]" belt and the [[resonant trans-Neptunian object]]s.<ref name="physical" /> The latter have orbits whose periods are in a simple ratio to that of Neptune: for example, going around the Sun twice for every three times that Neptune does, or once for every two. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 to 47.7&nbsp;AU.<ref>{{Cite journal |last1=Buie |first1=M. W. |last2=Millis |first2=R. L. |last3=Wasserman |first3=L. H. |last4=Elliot |first4=J. L. |last5=Kern |first5=S. D. |last6=Clancy |first6=K. B. |last7=Chiang |first7=E. I. |last8=Jordan |first8=A. B. |last9=Meech |first9=K. J. |last10=Wagner |first10=R. M. |last11=Trilling |first11=D. E. |date=2005 |title=Procedures, Resources and Selected Results of the Deep Ecliptic Survey |journal=[[Earth, Moon, and Planets]] |volume=92 |issue=1 |pages=113–124 |arxiv=astro-ph/0309251 |bibcode=2003EM&P...92..113B |doi=10.1023/B:MOON.0000031930.13823.be |s2cid=14820512}}</ref> Members of the classical Kuiper belt are sometimes called "cubewanos", after the first of their kind to be discovered, originally designated [[15760 Albion|1992 ''QB<sub>1</sub>'']], (and has since been named Albion); they are still in near primordial, low-eccentricity orbits.<ref>{{Cite journal |last1=Dotto |first1=E. |last2=Barucci |first2=M. A. |last3=Fulchignoni |first3=M. |date=1 January 2003 |title=Beyond Neptune, the new frontier of the Solar System |url=http://sait.oat.ts.astro.it/MSAIS/3/PDF/20.pdf |url-status=live |journal=Memorie della Societa Astronomica Italiana Supplementi |volume=3 |page=20 |bibcode=2003MSAIS...3...20D |issn=0037-8720 |archive-url=https://web.archive.org/web/20140825122005/http://sait.oat.ts.astro.it/MSAIS/3/PDF/20.pdf |archive-date=25 August 2014 |access-date=26 December 2006}}</ref>

There is strong consensus among astronomers that five members of the Kuiper belt are {{Visible anchor|Others|text=dwarf planets}}.<ref name="Grundy2019" /><ref name="JWST">{{cite journal |arxiv=2309.15230 |first1=J. P. |last1=Emery |first2=I. |last2=Wong |author-link= |title=A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy |date=2024 |first3=R. |last3=Brunetto |first4=J. C. |last4=Cook |first5=N. |last5=Pinilla-Alonso |first6=J. A. |last6=Stansberry |first7=B. J. |last7=Holler |first8=W. M. |last8=Grundy |first9=S. |last9=Protopapa |first10=A. C. |last10=Souza-Feliciano |first11=E. |last11=Fernández-Valenzuela |first12=J. I. |last12=Lunine |first13=D. C. |last13=Hines|journal=Icarus |volume=414 |doi=10.1016/j.icarus.2024.116017 |bibcode=2024Icar..41416017E }}</ref> Many dwarf planet candidates are being considered, pending further data for verification.<ref name="Tancredi2008">{{Cite journal |last1=Tancredi |first1=G. |last2=Favre |first2=S. A. |year=2008 |title=Which are the dwarfs in the Solar System? |journal=Icarus |volume=195 |issue=2 |pages=851–862 |bibcode=2008Icar..195..851T |doi=10.1016/j.icarus.2007.12.020}}</ref>

* {{Visible anchor|Pluto and Charon|text=[[Pluto]]}} (29.7–49.3&nbsp;AU) is the largest known object in the Kuiper belt. Pluto has a relatively eccentric orbit, inclined 17 degrees to the [[ecliptic plane]]. Pluto has a [[Orbital resonance|2:3 resonance]] with Neptune, meaning that Pluto orbits twice around the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called [[plutino]]s.<ref name="Fajans_et_al_2001">{{Cite journal |last1=Fajans |first1=J. |last2=Frièdland |first2=L. |date=October 2001 |title=Autoresonant (nonstationary) excitation of pendulums, Plutinos, plasmas, and other nonlinear oscillators |url=http://ist-socrates.berkeley.edu/~fajans/pub/pdffiles/AutoPendAJP.pdf |url-status=dead |journal=[[American Journal of Physics]] |volume=69 |issue=10 |pages=1096–1102 |bibcode=2001AmJPh..69.1096F |doi=10.1119/1.1389278 |archive-url=https://web.archive.org/web/20110607210435/http://ist-socrates.berkeley.edu/~fajans/pub/pdffiles/AutoPendAJP.pdf |archive-date=7 June 2011 |access-date=26 December 2006}}</ref> [[Moons of Pluto|Pluto has five moons]]: Charon, [[Styx (moon)|Styx]], [[Nix (moon)|Nix]], [[Kerberos (moon)|Kerberos]], and [[Hydra (moon)|Hydra]].<ref>{{Cite web |date=6 August 2021 |title=In Depth: Pluto |url=https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth |url-status=live |archive-url=https://web.archive.org/web/20220331112026/https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth |archive-date=31 March 2022 |access-date=31 March 2022 |website=NASA Science: Solar System Exploration}}</ref>
** [[Charon (moon)|Charon]], the largest of Pluto's moons, is sometimes described as part of a [[binary system (astronomy)|binary system]] with Pluto, as the two bodies orbit a [[barycenter]] of gravity above their surfaces (i.e. they appear to "orbit each other").
* {{Dp|Orcus}} (30.3–48.1&nbsp;AU), is in the same 2:3 orbital resonance with Neptune as Pluto, and is the largest such object after Pluto itself.<ref name="brownlargest" /> Its eccentricity and inclination are similar to Pluto's, but its perihelion lies about 120° from that of Pluto. Thus, the [[Phase (waves)#Phase difference|phase]] of Orcus's orbit is opposite to Pluto's: Orcus is at aphelion (most recently in 2019) around when Pluto is at perihelion (most recently in 1989) and vice versa.<ref name="MPC2004-D15">{{Cite web |date=20 February 2004 |title=MPEC 2004-D15 : 2004 DW |url=http://www.minorplanetcenter.net/mpec/K04/K04D15.html |url-status=live |archive-url=https://web.archive.org/web/20160303232947/http://www.minorplanetcenter.net/mpec/K04/K04D15.html |archive-date=3 March 2016 |access-date=5 July 2011 |publisher=Minor Planet Center}}</ref> For this reason, it has been called the ''anti-Pluto''.<ref name="MBP">{{Cite web |last=Michael E. Brown |author-link=Michael E. Brown |date=23 March 2009 |title=S/2005 (90482) 1 needs your help |url=http://www.mikebrownsplanets.com/2009/03/s1-90482-2005-needs-your-help.html |url-status=live |archive-url=https://web.archive.org/web/20090328012339/http://www.mikebrownsplanets.com/2009/03/s1-90482-2005-needs-your-help.html |archive-date=28 March 2009 |access-date=25 March 2009 |publisher=Mike Brown's Planets (blog)}}</ref><ref>{{Cite book |last=Moltenbrey |first=Michael |url=https://www.worldcat.org/oclc/926914921 |title=Dawn of Small Worlds: Dwarf planets, asteroids, comets |date=2016 |publisher=Springer |isbn=978-3-319-23003-0 |location=Cham |page=171 |oclc=926914921 |access-date=9 April 2022 |archive-url=https://web.archive.org/web/20220420161222/https://www.worldcat.org/title/dawn-of-small-worlds-dwarf-planets-asteroids-comets/oclc/926914921 |archive-date=20 April 2022 |url-status=live}}</ref> It has one known moon, [[Vanth (moon)|Vanth]].<ref name="IAUC8812">{{Cite web |last=Green |first=Daniel W. E. |date=22 February 2007 |title=IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637), (90482) |url=http://www.cbat.eps.harvard.edu/iauc/08800/08812.html |url-status=live |archive-url=https://web.archive.org/web/20120314060043/http://cbat.eps.harvard.edu/iauc/08800/08812.html |archive-date=14 March 2012 |access-date=4 July 2011 |publisher=International Astronomical Union Circular}}</ref>
* [[Haumea]] (34.6–51.6&nbsp;AU) was discovered in 2005.<ref>{{Cite web |date=17 September 2008 |title=IAU names fifth dwarf planet Haumea |url=https://www.iau.org/news/pressreleases/detail/iau0807 |url-status=live |archive-url=https://web.archive.org/web/20140425065601/http://iau.org/public_press/news/detail/iau0807 |archive-date=25 April 2014 |access-date=9 April 2022 |website=International Astronomical Union}}</ref> It is in a temporary 7:12 orbital resonance with Neptune.<ref name="brownlargest">{{Cite book |last=Brown |first=Mike |title=The Solar System Beyond Neptune |publisher=University of Arizona Press |year=2008 |isbn=978-0-816-52755-7 |editor-last=Barucci |editor-first=M. Antonietta |pages=335–344 |chapter=The largest Kuiper belt objects |oclc=1063456240 |author-link=Mike Brown (astronomer) |access-date=9 April 2022 |chapter-url=http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf |archive-url=https://web.archive.org/web/20121113114533/http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf |archive-date=13 November 2012 |url-status=live}}</ref> Haumea possesses a ring system, two known moons named [[Hiʻiaka (moon)|Hiʻiaka]] and [[Namaka (moon)|Namaka]], and rotates so quickly (once every 3.9 hours) that it is stretched into an [[ellipsoid]]. It is part of a [[collisional family]] of Kuiper belt objects that share similar orbits, which suggests a giant impact on Haumea ejected fragments into space billions of years ago.<ref name="Noviello2022">{{Cite journal |last1=Noviello |first1=Jessica L. |last2=Desch |first2=Stephen J. |last3=Neveu |first3=Marc |last4=Proudfoot |first4=Benjamin C. N. |last5=Sonnett |first5=Sarah |date=September 2022 |title=Let It Go: Geophysically Driven Ejection of the Haumea Family Members |journal=The Planetary Science Journal |volume=3 |issue=9 |page=19 |bibcode=2022PSJ.....3..225N |doi=10.3847/PSJ/ac8e03 |s2cid=252620869 |id=225 |doi-access=free}}</ref>
* [[Makemake]] (38.1–52.8&nbsp;AU), although smaller than Pluto, is the largest known object in the ''classical'' Kuiper belt (that is, a Kuiper belt object not in a confirmed resonance with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. Discovered in 2005, it was officially named in 2009.<ref>{{Cite web |date=19 July 2009 |title=Fourth dwarf planet named Makemake |url=https://www.iau.org/news/pressreleases/detail/iau0806 |url-status=live |archive-url=https://web.archive.org/web/20170730222925/https://www.iau.org/news/pressreleases/detail/iau0806 |archive-date=30 July 2017 |access-date=9 April 2022 |website=International Astronomical Union}}</ref> Its orbit is far more inclined than Pluto's, at 29°.<ref name="Buie136472">{{Cite web |last=Buie |first=Marc W. |author-link=Marc W. Buie |date=5 April 2008 |title=Orbit Fit and Astrometric record for 136472 |url=http://www.boulder.swri.edu/~buie/kbo/astrom/136472.html |url-status=live |archive-url=https://web.archive.org/web/20200527191044/https://www.boulder.swri.edu/~buie/kbo/astrom/136472.html |archive-date=27 May 2020 |access-date=15 July 2012 |publisher=SwRI (Space Science Department)}}</ref> It has one known moon, [[S/2015 (136472) 1]].<ref name="ParkerA2016">{{Cite journal |last1=Parker |first1=A. H. |last2=Buie |first2=M. W. |last3=Grundy |first3=W. M. |last4=Noll |first4=K. S. |date=25 April 2016 |title=Discovery of a Makemakean Moon |journal=[[The Astrophysical Journal]] |volume=825 |issue=1 |page=L9 |arxiv=1604.07461 |bibcode=2016ApJ...825L...9P |doi=10.3847/2041-8205/825/1/L9 |s2cid=119270442 |doi-access=free}}</ref>
* {{Dp|Quaoar}} (41.9–45.5&nbsp;AU) is the second-largest known object in the classical Kuiper belt, after Makemake. Its orbit is significantly less eccentric and inclined than those of Makemake or Haumea.<ref name="brownlargest" /> It possesses a ring system and one known moon, [[Weywot (moon)|Weywot]].<ref name="Morgado2023">{{Cite Q|Q116754015|display-authors=1}}</ref>

=== Scattered disc ===
{{Main|Scattered disc}}

[[File:TheKuiperBelt Projections 100AU Classical SDO.svg|thumb|The orbital eccentricities and inclinations of the scattered disc population compared to the classical and resonant Kuiper belt objects]]
The scattered disc, which overlaps the Kuiper belt but extends out to near 500&nbsp;AU, is thought to be the source of short-period comets. Scattered-disc objects are believed to have been perturbed into erratic orbits by the gravitational influence of [[Formation and evolution of the Solar System#Planetary migration|Neptune's early outward migration]]. Most scattered disc objects have perihelia within the Kuiper belt but aphelia far beyond it (some more than 150&nbsp;AU from the Sun). SDOs' orbits can be inclined up to 46.8° from the ecliptic plane.<ref>{{Cite book |last1=Gomes |first1=R. S. |url=https://www.lpi.usra.edu/books/ssbn2008/7003.pdf |title=The Solar System Beyond Neptune |last2=Fernández |first2=J. A. |last3=Gallardo |first3=T. |last4=Brunini |first4=A. |date=2008 |publisher=University of Arizona Press |isbn=978-0816527557 |pages=259–273 |chapter=The Scattered Disk: Origins, Dynamics, and End States |access-date=12 May 2022 |archive-url=https://web.archive.org/web/20220121172507/https://www.lpi.usra.edu/books/ssbn2008/7003.pdf |archive-date=21 January 2022 |url-status=live}}</ref> Some astronomers consider the scattered disc to be merely another region of the Kuiper belt and describe scattered-disc objects as "scattered Kuiper belt objects".<ref>{{Cite web |last=Jewitt |first=David |date=2005 |title=The 1,000 km Scale KBOs |url=http://www2.ess.ucla.edu/~jewitt/kb/big_kbo.html |url-status=live |archive-url=https://web.archive.org/web/20140609134900/http://www2.ess.ucla.edu/~jewitt/kb/big_kbo.html |archive-date=9 June 2014 |access-date=16 July 2006 |website=University of Hawaii}}</ref> Some astronomers classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.<ref>{{Cite web |title=List of Centaurs and Scattered-Disk Objects |url=http://www.minorplanetcenter.org/iau/lists/Centaurs.html |url-status=live |archive-url=https://web.archive.org/web/20170629210646/http://www.minorplanetcenter.org/iau/lists/Centaurs.html |archive-date=29 June 2017 |access-date=2 April 2007 |website=IAU: Minor Planet Center}}</ref>

Currently, there is strong consensus among astronomers that two of the bodies in the scattered disc are {{Visible anchor|Gonggong and Eris|text=dwarf planets}}:

* {{Dp|Eris}} (38.3–97.5&nbsp;AU) is the largest known scattered disc object and the most massive known dwarf planet. Eris's discovery contributed to a debate about the definition of a planet because it is 25% more massive than Pluto<ref name="Brown Schaller 2007">{{Cite journal |last1=Brown |first1=Michael E. |author-link=Michael E. Brown |last2=Schaller |first2=Emily L. |date=15 June 2007 |title=The Mass of Dwarf Planet Eris |journal=Science |volume=316 |issue=5831 |page=1585 |bibcode=2007Sci...316.1585B |doi=10.1126/science.1139415 |pmid=17569855 |s2cid=21468196|url=https://resolver.caltech.edu/CaltechAUTHORS:20121001-135149660 }}</ref> and about the same diameter. It has one known moon, [[Dysnomia (moon)|Dysnomia]]. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2&nbsp;AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane at an angle of 44°.<ref>{{Cite journal |last1=Dumas |first1=C. |last2=Merlin |first2=F. |last3=Barucci |first3=M. A. |last4=de Bergh |first4=C. |last5=Hainault |first5=O. |last6=Guilbert |first6=A. |last7=Vernazza |first7=P. |last8=Doressoundiram |first8=A. |date=August 2007 |title=Surface composition of the largest dwarf planet 136199 Eris (2003 UB{313}) |journal=Astronomy and Astrophysics |volume=471 |issue=1 |pages=331–334 |bibcode=2007A&A...471..331D |doi=10.1051/0004-6361:20066665 |doi-access=free}}</ref>
* {{Dp|Gonggong}} (33.8–101.2&nbsp;AU) is a dwarf planet in a comparable orbit to Eris, except that it is in a 3:10 resonance with Neptune.<ref name="jpldata" group="D">{{Cite web |date=10 April 2017 |title=JPL Small-Body Database Browser: 225088 Gonggong (2007 OR10) |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2225088 |url-status=live |archive-url=https://web.archive.org/web/20200610013703/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2225088 |archive-date=10 June 2020 |access-date=20 February 2020 |publisher=[[Jet Propulsion Laboratory]] |type=20 September 2015 last obs.}}</ref> It has one known moon, [[Xiangliu (moon)|Xiangliu]].<ref name="Kissetal2017">{{Cite journal |last1=Kiss |first1=Csaba |last2=Marton |first2=Gábor |last3=Farkas-Takács |first3=Anikó |last4=Stansberry |first4=John |last5=Müller |first5=Thomas |last6=Vinkó |first6=József |last7=Balog |first7=Zoltán |last8=Ortiz |first8=Jose-Luis |last9=Pál |first9=András |date=16 March 2017 |title=Discovery of a Satellite of the Large Trans-Neptunian Object (225088) 2007 OR<sub>10</sub> |journal=[[The Astrophysical Journal Letters]] |volume=838 |page=5 |arxiv=1703.01407 |bibcode=2017ApJ...838L...1K |doi=10.3847/2041-8213/aa6484 |s2cid=46766640 |id=L1 |doi-access=free |number=1}}</ref>

=== Extreme trans-Neptunian objects<span class="anchor" id="Detached objects"></span>===
{{Main|Extreme trans-Neptunian object}}
[[File:Distant object orbits + Planet Nine.png|thumb|upright=1.3|The current orbits of [[90377 Sedna|Sedna]], [[2012 VP113]], [[541132 Leleākūhonua|Leleākūhonua]] (pink), and other very [[ETNO|distant objects]] (red, brown and cyan) along with the predicted orbit of the hypothetical [[Planet Nine]] (dark blue)]]

Some objects in the Solar System have a very large orbit, and therefore are much less affected by the known giant planets than other minor planet populations. These bodies are called extreme trans-Neptunian objects, or ETNOs for short.<ref name="Sheppard-2018">{{cite journal |last1=Sheppard |first1=Scott S. |last2=Trujillo |first2=Chadwick A. |last3=Tholen |first3=David J. |last4=Kaib |first4=Nathan |year=2019 |title=A New High Perihelion Trans-Plutonian Inner Oort Cloud Object: 2015 TG387 |journal=The Astronomical Journal |volume=157 |issue=4 |page=139 |arxiv=1810.00013 |bibcode=2019AJ....157..139S |doi=10.3847/1538-3881/ab0895 |s2cid=119071596 |doi-access=free}}</ref> Generally, ETNOs' [[semi-major axis|semi-major axes]] are at least 150–250&nbsp;AU wide.<ref name="Sheppard-2018" /><ref name="Caju_outlier">{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=12 September 2018 |title=A Fruit of a Different Kind: 2015 BP<sub>519</sub> as an Outlier among the Extreme Trans-Neptunian Objects |journal=[[Research Notes of the AAS]] |volume=2 |issue=3 |pages=167 |arxiv=1809.02571 |bibcode=2018RNAAS...2..167D |doi=10.3847/2515-5172/aadfec |s2cid=119433944 |doi-access=free}}</ref> For example, [[541132 Leleākūhonua]] orbits the Sun once every ~32,000&nbsp;years, with a distance of 65–2000&nbsp;AU from the Sun.<ref name="jpldata2" group="D">{{cite web |title=JPL Small-Body Database Browser: (2015 TG387) |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3830896 |access-date=13 December 2018 |publisher=[[Jet Propulsion Laboratory]] |type=2018-10-17 last obs. |archive-date=14 April 2020 |archive-url=https://web.archive.org/web/20200414180200/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3830896 |url-status=live }}</ref>

This population is divided into three subgroups by astronomers. The [[Scattered disc object|scattered]] ETNOs have [[perihelia]] around 38–45&nbsp;AU and an exceptionally high [[Orbital eccentricity|eccentricity]] of more than 0.85. As with the regular scattered disc objects, they were likely formed as result of [[Planetary migration#Gravitational scattering|gravitational scattering]] by Neptune and still interact with the giant planets. The [[Detached object|detached]] ETNOs, with perihelia approximately between 40–45 and 50–60&nbsp;AU, are less affected by Neptune than the scattered ETNOs, but are still relatively close to Neptune. The [[sednoid]]s or [[Hills Cloud|inner Oort cloud]] objects, with perihelia beyond 50–60&nbsp;AU, are too far from Neptune to be strongly influenced by it.<ref name="Sheppard-2018" />

Currently, there is one ETNO that is classified as a dwarf planet:

* {{Dp|Sedna}} (76.2–937&nbsp;AU) was the first extreme trans-Neptunian object to be discovered. It is a large, reddish object, and it takes ~11,400&nbsp;years for Sedna to complete one orbit. [[Michael E. Brown|Mike Brown]], who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt because its perihelion is too distant to have been affected by Neptune's migration.<ref>{{Cite web |last=Jewitt |first=David |date=2004 |title=Sedna – 2003 VB<sub>12</sub> |url=http://www2.ess.ucla.edu/~jewitt/kb/sedna.html |url-status=live |archive-url=https://web.archive.org/web/20110716032018/http://www2.ess.ucla.edu/~jewitt/kb/sedna.html |archive-date=16 July 2011 |access-date=23 June 2006 |website=University of Hawaii}}</ref> The [[Sednoid|sednoid population]] is named after Sedna.<ref name="Sheppard-2018" />

=== Edge of the heliosphere ===
[[File:Magnetosphere Levels.jpg|thumb|Diagram of the Sun's magnetosphere and helioshealth]]

{{Anchor|Heliopause}}The Sun's [[stellar-wind bubble]], the [[heliosphere]], a region of space dominated by the Sun, has its boundary at the ''termination shock''. Based on the Sun's [[peculiar motion]] relative to the [[local standard of rest]], this boundary is roughly 80–100&nbsp;AU from the Sun upwind of the interstellar medium and roughly 200&nbsp;AU from the Sun downwind.<ref name="fahr">{{Cite journal |last1=Fahr |first1=H. J. |last2=Kausch |first2=T. |last3=Scherer |first3=H. |date=2000 |title=A 5-fluid hydrodynamic approach to model the Solar System-interstellar medium interaction |url=http://aa.springer.de/papers/0357001/2300268.pdf |url-status=dead |journal=[[Astronomy & Astrophysics]] |volume=357 |page=268 |bibcode=2000A&A...357..268F |archive-url=https://web.archive.org/web/20170808135422/http://aa.springer.de/papers/0357001/2300268.pdf |archive-date=8 August 2017 |access-date=24 August 2008}} See Figures 1 and 2.</ref> Here the solar wind collides with the interstellar medium<ref>{{Cite web |last=Hatfield |first=Miles |date=3 June 2021 |title=The Heliopedia |url=http://www.nasa.gov/mission_pages/sunearth/the-heliopedia |url-status=live |archive-url=https://web.archive.org/web/20220325142928/https://www.nasa.gov/mission_pages/sunearth/the-heliopedia |archive-date=25 March 2022 |access-date=29 March 2022 |website=NASA}}</ref> and dramatically slows, condenses and becomes more turbulent, forming a great oval structure known as the [[heliosheath]].<ref name="fahr" />

The heliosheath has been theorized to look and behave very much like a comet's tail, extending outward for a further 40&nbsp;AU on the upwind side but tailing many times that distance downwind to possibly several thousands of AU.<ref name="n092">{{cite journal | last1=Brandt | first1=P. C. | last2=Provornikova | first2=E. | last3=Bale | first3=S. D. | last4=Cocoros | first4=A. | last5=DeMajistre | first5=R. | last6=Dialynas | first6=K. | last7=Elliott | first7=H. A. | last8=Eriksson | first8=S. | last9=Fields | first9=B. | last10=Galli | first10=A. | last11=Hill | first11=M. E. | last12=Horanyi | first12=M. | last13=Horbury | first13=T. | last14=Hunziker | first14=S. | last15=Kollmann | first15=P. | last16=Kinnison | first16=J. | last17=Fountain | first17=G. | last18=Krimigis | first18=S. M. | last19=Kurth | first19=W. S. | last20=Linsky | first20=J. | last21=Lisse | first21=C. M. | last22=Mandt | first22=K. E. | last23=Magnes | first23=W. | last24=McNutt | first24=R. L. | last25=Miller | first25=J. | last26=Moebius | first26=E. | last27=Mostafavi | first27=P. | last28=Opher | first28=M. | last29=Paxton | first29=L. | last30=Plaschke | first30=F. | last31=Poppe | first31=A. R. | last32=Roelof | first32=E. C. | last33=Runyon | first33=K. | last34=Redfield | first34=S. | last35=Schwadron | first35=N. | last36=Sterken | first36=V. | last37=Swaczyna | first37=P. | last38=Szalay | first38=J. | last39=Turner | first39=D. | last40=Vannier | first40=H. | last41=Wimmer-Schweingruber | first41=R. | last42=Wurz | first42=P. | last43=Zirnstein | first43=E. J. | title=Future Exploration of the Outer Heliosphere and Very Local Interstellar Medium by Interstellar Probe | journal=Space Science Reviews | volume=219 | issue=2 | date=2023 | issn=0038-6308 | pmid=36874191 | pmc=9974711 | doi=10.1007/s11214-022-00943-x | page=18| bibcode=2023SSRv..219...18B }}</ref><ref>{{Cite journal |last1=Baranov |first1=V. B. |last2=Malama |first2=Yu. G. |date=1993 |title=Model of the solar wind interaction with the local interstellar medium: Numerical solution of self-consistent problem |url=http://doi.wiley.com/10.1029/93JA01171 |journal=Journal of Geophysical Research |language=en |volume=98 |issue=A9 |page=15157 |bibcode=1993JGR....9815157B |doi=10.1029/93JA01171 |issn=0148-0227 |access-date=9 April 2022 |archive-date=20 April 2022 |archive-url=https://web.archive.org/web/20220420161220/https://onlinelibrary.wiley.com/resolve/doi?DOI=10.1029%2F93JA01171 |url-status=live }}</ref> Evidence from the ''[[Cassini (spacecraft)|Cassini]]'' and [[Interstellar Boundary Explorer]] spacecraft has suggested that it is forced into a bubble shape by the constraining action of the interstellar magnetic field,<ref>{{Cite web |date=19 November 2009 |title=Cassini's Big Sky: The View from the Center of Our Solar System |url=https://www.jpl.nasa.gov/news/cassinis-big-sky-the-view-from-the-center-of-our-solar-system |url-status=live |archive-url=https://web.archive.org/web/20220409213721/https://www.jpl.nasa.gov/news/cassinis-big-sky-the-view-from-the-center-of-our-solar-system |archive-date=9 April 2022 |access-date=9 April 2022 |website=Jet Propulsion Laboratory}}</ref><ref>{{Cite journal |last1=Kornbleuth |first1=M. |last2=Opher |first2=M. |last3=Baliukin |first3=I. |last4=Gkioulidou |first4=M. |last5=Richardson |first5=J. D. |last6=Zank |first6=G. P. |last7=Michael |first7=A. T. |last8=Tóth |first8=G. |last9=Tenishev |first9=V. |last10=Izmodenov |first10=V. |last11=Alexashov |first11=D. |date=1 December 2021 |title=The Development of a Split-tail Heliosphere and the Role of Non-ideal Processes: A Comparison of the BU and Moscow Models |journal=[[The Astrophysical Journal]] |volume=923 |issue=2 |page=179 |arxiv=2110.13962 |bibcode=2021ApJ...923..179K |doi=10.3847/1538-4357/ac2fa6 |issn=0004-637X |s2cid=239998560 |doi-access=free}}</ref> but the actual shape remains unknown.<ref>{{Cite journal |last1=Reisenfeld |first1=Daniel B. |last2=Bzowski |first2=Maciej |last3=Funsten |first3=Herbert O. |last4=Heerikhuisen |first4=Jacob |last5=Janzen |first5=Paul H. |last6=Kubiak |first6=Marzena A. |last7=McComas |first7=David J. |last8=Schwadron |first8=Nathan A. |last9=Sokół |first9=Justyna M. |last10=Zimorino |first10=Alex |last11=Zirnstein |first11=Eric J. |date=1 June 2021 |title=A Three-dimensional Map of the Heliosphere from IBEX |journal=[[The Astrophysical Journal Supplement Series]] |volume=254 |issue=2 |page=40 |bibcode=2021ApJS..254...40R |doi=10.3847/1538-4365/abf658 |issn=0067-0049 |osti=1890983 |s2cid=235400678 |doi-access=free}}</ref>

The shape and form of the outer edge of the heliosphere is likely affected by the [[fluid dynamics]] of interactions with the interstellar medium as well as [[solar magnetic field]]s prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9&nbsp;AU farther than the southern hemisphere.<ref name="fahr" /> The heliopause is considered the beginning of the interstellar medium.<ref name="Voyager" /> Beyond the heliopause, at around 230&nbsp;AU, lies the [[bow shock]]: a plasma "wake" left by the Sun as it travels through the Milky Way.<ref>{{Cite APOD|date=24 June 2002|title=The Sun's Heliosphere & Heliopause|access-date=23 June 2006}}</ref> Large objects outside the heliopause remain gravitationally bound to the Sun, but the flow of matter in the interstellar medium homogenizes the distribution of micro-scale objects.<ref name="Voyager" />

== Miscellaneous populations ==
=== Comets ===
{{Main|Comet}}

[[File:Comet_Hale-Bopp_1995O1.jpg|thumb|[[Comet Hale–Bopp]] seen in 1997]]
Comets are [[small Solar System bodies]], typically only a few kilometers across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to [[sublimation (chemistry)|sublimate]] and [[ion]]ise, creating a [[coma (cometary)|coma]]: a long tail of gas and dust often visible to the naked eye.<ref>{{Cite web |date=19 December 2019 |title=In Depth: Comets |url=https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/in-depth |url-status=live |archive-url=https://web.archive.org/web/20220331200633/https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/in-depth |archive-date=31 March 2022 |access-date=31 March 2022 |website=NASA Science: Solar System Exploration}}</ref>

Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are thought to originate in the Kuiper belt, whereas long-period comets, such as [[Comet Hale–Bopp|Hale–Bopp]], are thought to originate in the Oort cloud. Many comet groups, such as the [[Kreutz sungrazer]]s, formed from the breakup of a single parent.<ref>{{Cite journal |last=Sekanina |first=Zdeněk |date=2001 |title=Kreutz sungrazers: the ultimate case of cometary fragmentation and disintegration? |journal=Publications of the Astronomical Institute of the Academy of Sciences of the Czech Republic |volume=89 |pages=78–93 |bibcode=2001PAICz..89...78S}}</ref> Some comets with [[hyperbolic trajectory|hyperbolic]] orbits may originate outside the Solar System, but determining their precise orbits is difficult.<ref name="hyperbolic">{{Cite journal |last=Królikowska |first=M. |date=2001 |title=A study of the original orbits of ''hyperbolic'' comets |journal=[[Astronomy & Astrophysics]] |volume=376 |issue=1 |pages=316–324 |bibcode=2001A&A...376..316K |doi=10.1051/0004-6361:20010945 |doi-access=free}}</ref> Old comets whose volatiles have mostly been driven out by solar warming are often categorized as asteroids.<ref>{{Cite journal |last=Whipple |first=Fred L. |date=1992 |title=The activities of comets related to their aging and origin |journal=[[Celestial Mechanics and Dynamical Astronomy]] |volume=54 |issue=1–3 |pages=1–11 |bibcode=1992CeMDA..54....1W |doi=10.1007/BF00049540 |s2cid=189827311}}</ref>

=== Meteoroids, meteors and dust ===
{{Main|Meteoroid|Interplanetary dust cloud|Cosmic dust}}
[[File:Meteor shower in the Chilean Desert (annotated and cropped).jpg|thumb|The planets, zodiacal light and meteor shower (top left of image)]]
Solid objects smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), with the exact division between the two categories being debated over the years.<ref>{{Cite journal |last1=Rubin |first1=Alan E. |last2=Grossman |first2=Jeffrey N. |date=February 2010 |title=Meteorite and meteoroid: new comprehensive definitions |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2009.01009.x |url-status=live |journal=Meteoritics and Planetary Science |language=en |volume=45 |issue=1 |page=114 |bibcode=2010M&PS...45..114R |doi=10.1111/j.1945-5100.2009.01009.x |s2cid=129972426 |archive-url=https://web.archive.org/web/20220325111938/https://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2009.01009.x |archive-date=25 March 2022 |access-date=10 April 2022}}</ref> By 2017, the IAU designated any solid object having a diameter between ~30&nbsp;[[Micrometre|micrometers]] and 1&nbsp;meter as meteoroids, and depreciated the micrometeoroid categorization, instead terms smaller particles simply as 'dust particles'.<ref>{{cite web |last1= |date=30 April 2017 |title=Definition of terms in meteor astronomy |url=https://www.iau.org/static/science/scientific_bodies/commissions/f1/meteordefinitions_approved.pdf |access-date=25 July 2020 |website=International Astronomical Union |publisher=IAU Commission F1 |page=2 |archive-date=22 December 2021 |archive-url=https://web.archive.org/web/20211222205136/https://www.iau.org/static/science/scientific_bodies/commissions/f1/meteordefinitions_approved.pdf |url-status=live }}</ref>

Some meteoroids formed via disintegration of comets and asteroids, while a few formed via impact debris ejected from planetary bodies. Most meteoroids are made of silicates and heavier metals like [[nickel]] and [[iron]].<ref>{{cite web |title=Meteoroid |url=http://education.nationalgeographic.co.uk/encyclopedia/meteoroid/ |archive-url=https://web.archive.org/web/20151007141358/https://education.nationalgeographic.co.uk/encyclopedia/meteoroid/ |archive-date=7 October 2015 |access-date=24 August 2015 |work=National Geographic|date=28 May 2010 }}</ref> When passing through the Solar System, comets produce a trail of meteoroids; it is hypothesized that this is caused either by vaporization of the comet's material or by simple breakup of dormant comets. When crossing an atmosphere, these meteoroids will produce bright streaks in the sky due to [[atmospheric entry]], called [[meteor]]s. If a stream of meteoroids enter the atmosphere on parallel trajectories, the meteors will seemingly 'radiate' from a point in the sky, hence the phenomenon's name: [[meteor shower]].<ref>{{cite book | chapter=The Evolution of Meteoroid Streams | first=Iwan P. | last=Williams | title=Meteors in the Earth's Atmosphere: Meteoroids and Cosmic Dust and Their Interactions with the Earth's Upper Atmosphere | pages=13–32 | year=2002 | isbn=9780521804318 | publisher=Cambridge University Press | editor1-first=Edmond | editor1-last=Murad | editor2-first=Iwan P. | editor2-last=Williams | chapter-url=https://books.google.com/books?id=eqd4e34uE-MC&pg=PA13 }}</ref>

The inner Solar System is home to the [[interplanetary dust cloud|zodiacal dust cloud]], which is visible as the hazy [[zodiacal light]] in dark, unpolluted skies. It may be generated by collisions within the asteroid belt brought on by gravitational interactions with the planets; a more recent proposed origin is materials from planet Mars.<ref>{{Cite journal |last1=Jorgensen |first1=J. L. |last2=Benn |first2=M. |last3=Connerney |first3=J. E. P. |last4=Denver |first4=T. |last5=Jorgensen |first5=P. S. |last6=Andersen |first6=A. C. |last7=Bolton |first7=S. J. |date=March 2021 |title=Distribution of Interplanetary Dust Detected by the Juno Spacecraft and Its Contribution to the Zodiacal Light |journal=Journal of Geophysical Research: Planets |language=en |volume=126 |issue=3 |bibcode=2021JGRE..12606509J |doi=10.1029/2020JE006509 |issn=2169-9097 |s2cid=228840132 |doi-access=free}}</ref> The outer Solar System hosts a cosmic dust cloud. It extends from about {{val|10|u=AU}} to about {{val|40|u=AU}}, and was probably created by collisions within the Kuiper belt.<ref>{{Cite web |date=2003 |title=ESA scientist discovers a way to shortlist stars that might have planets |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=29471 |url-status=live |archive-url=https://web.archive.org/web/20130502033116/http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=29471 |archive-date=2 May 2013 |access-date=3 February 2007 |website=ESA Science and Technology}}</ref><ref>{{Cite journal |last1=Landgraf |first1=M. |last2=Liou |first2=J.-C. |last3=Zook |first3=H. A. |last4=Grün |first4=E. |date=May 2002 |title=Origins of Solar System Dust beyond Jupiter |url=http://astron.berkeley.edu/~kalas/disksite/library/ladgraf02.pdf |url-status=live |journal=[[The Astronomical Journal]] |volume=123 |issue=5 |pages=2857–2861 |arxiv=astro-ph/0201291 |bibcode=2002AJ....123.2857L |doi=10.1086/339704 |s2cid=38710056 |archive-url=http://arquivo.pt/wayback/20160515115002/http://astron.berkeley.edu/~kalas/disksite/library/ladgraf02.pdf |archive-date=15 May 2016 |access-date=9 February 2007}}</ref>

== Boundary region and uncertainties ==
{{See also|Planets beyond Neptune|Planet Nine|List of Solar System objects by greatest aphelion}}

[[File:Kuiper oort-en.svg|thumb|An [[artist's impression]] of the [[Oort cloud]], a region still well within the [[Sphere of influence (astrodynamics)|sphere of influence]] of the Solar System, including a depiction of the much further inside [[Kuiper belt]] (inset); the sizes of objects are over-scaled for visibility.]]

{{Anchor|Farthest regions|Boundaries}}Much of the Solar System is still unknown. Regions beyond thousands of AU away are still virtually unmapped and learning about this region of space is difficult. Study in this region depends upon inferences from those few objects whose orbits happen to be perturbed such that they fall closer to the Sun, and even then, detecting these objects has often been possible only when they happened to become bright enough to register as comets.<ref>{{Cite journal |last1=Bernardinelli |first1=Pedro H. |last2=Bernstein |first2=Gary M. |last3=Montet |first3=Benjamin T. |last4=Weryk |first4=Robert |last5=Wainscoat |first5=Richard |last6=Aguena |first6=M. |last7=Allam |first7=S. |last8=Andrade-Oliveira |first8=F. |last9=Annis |first9=J. |last10=Avila |first10=S. |last11=Bertin |first11=E. |display-authors=3 |date=1 November 2021 |title=C/2014 UN 271 (Bernardinelli-Bernstein): The Nearly Spherical Cow of Comets |journal=[[The Astrophysical Journal Letters]] |volume=921 |issue=2 |page=L37 |arxiv=2109.09852 |bibcode=2021ApJ...921L..37B |doi=10.3847/2041-8213/ac32d3 |issn=2041-8205 |s2cid=237581632 |doi-access=free}}</ref> Many objects may yet be discovered in the Solar System's uncharted regions.<ref>{{Cite web |last=Loeffler |first=John |date=1 October 2021 |title=Our solar system may have a hidden planet beyond Neptune – no, not that one |url=https://www.msn.com/en-us/news/technology/our-solar-system-may-have-a-hidden-planet-beyond-neptune-no-not-that-one/ar-AAP3b0l?ocid=msedgntp |url-status=live |archive-url=https://web.archive.org/web/20211001203656/https://www.msn.com/en-us/news/technology/our-solar-system-may-have-a-hidden-planet-beyond-neptune-no-not-that-one/ar-AAP3b0l?ocid=msedgntp |archive-date=1 October 2021 |access-date=7 April 2022 |website=MSN}}</ref>

{{Anchor|Oort cloud}}The [[Oort cloud]] is a theorized spherical shell of up to a trillion icy objects that is thought to be the source for all long-period comets.<ref name=":5">{{Cite journal |vauthors=Stern SA, Weissman PR |date=2001 |title=Rapid collisional evolution of comets during the formation of the Oort cloud |journal=Nature |volume=409 |issue=6820 |pages=589–591 |bibcode=2001Natur.409..589S |doi=10.1038/35054508 |pmid=11214311 |s2cid=205013399}}</ref><ref name=":6">{{Cite web |last=Arnett |first=Bill |date=2006 |title=The Kuiper Belt and the Oort Cloud |url=http://www.nineplanets.org/kboc.html |url-status=live |archive-url=https://web.archive.org/web/20190807064224/http://nineplanets.org/kboc.html |archive-date=7 August 2019 |access-date=23 June 2006 |website=Nine Planets}}</ref> No direct observation of the Oort cloud is possible with present imaging technology.<ref>{{Cite web |title=Oort Cloud |url=https://solarsystem.nasa.gov/solar-system/oort-cloud/overview |url-status=live |archive-url=https://web.archive.org/web/20230630162050/https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/ |archive-date=30 June 2023 |access-date=1 July 2023 |website=NASA Solar System Exploration}}</ref> It is theorized to surround the Solar System at roughly 50,000&nbsp;AU (~0.9&nbsp;[[Light-year|ly]]) from the Sun and possibly to as far as 100,000&nbsp;AU (~1.8&nbsp;ly). The Oort cloud is thought to be composed of comets that were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events, such as collisions, the gravitational effects of a passing star, or the [[galactic tide]], the [[tidal force]] exerted by the Milky Way.<ref name=":5" /><ref name=":6" />

As of the 2020s, a few astronomers have hypothesized that [[Planet Nine]] (a planet beyond Neptune) might exist, based on statistical variance in the orbit of [[extreme trans-Neptunian object]]s.<ref name="P9H2019">{{cite journal |last1=Batygin |first1=Konstantin |last2=Adams |first2=Fred C. |last3=Brown |first3=Michael E. |last4=Becker |first4=Juliette C. |date=2019 |title=The Planet Nine Hypothesis |journal=[[Physics Reports]] |volume=805 |pages=1–53 |arxiv=1902.10103 |bibcode=2019PhR...805....1B |doi=10.1016/j.physrep.2019.01.009 |s2cid=119248548}}</ref> Their closest approaches to the Sun are mostly clustered around one sector and their orbits are similarly tilted, suggesting that a large planet might be influencing their orbit over millions of years.<ref name="Sheppard2014">{{cite journal |last1=Trujillo |first1=Chadwick A. |author-link=Chad Trujillo |last2=Sheppard |first2=Scott S. |author-link2=Scott S. Sheppard |date=2014 |title=A Sedna-like Body with a Perihelion of 80 Astronomical Units |url=http://home.dtm.ciw.edu/users/sheppard/pub/TrujilloSheppard2014.pdf |url-status=dead |journal=[[Nature (journal)|Nature]] |volume=507 |issue=7493 |pages=471–474 |bibcode=2014Natur.507..471T |doi=10.1038/nature13156 |pmid=24670765 |s2cid=4393431 |url-access=subscription |archive-url=https://web.archive.org/web/20141216183818/http://home.dtm.ciw.edu/users/sheppard/pub/TrujilloSheppard2014.pdf |archive-date=16 December 2014 |access-date=20 January 2016}}</ref><ref name="nodes-2021">{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=1 September 2021 |title=Peculiar orbits and asymmetries in extreme trans-Neptunian space |url=https://academic.oup.com/mnras/article-abstract/506/1/633/6307523 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=506 |issue=1 |pages=633–649 |arxiv=2106.08369 |bibcode=2021MNRAS.506..633D |doi=10.1093/mnras/stab1756 |doi-access=free |access-date=20 April 2024 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019195919/https://academic.oup.com/mnras/article-abstract/506/1/633/6307523 |url-status=live }}</ref><ref name="nodes-2022">{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=1 May 2022 |title=Twisted extreme trans-Neptunian orbital parameter space: statistically significant asymmetries confirmed |url=https://academic.oup.com/mnrasl/article-abstract/512/1/L6/6524836 |journal=[[Monthly Notices of the Royal Astronomical Society Letters]] |volume=512 |issue=1 |pages=L6–L10 |arxiv=2202.01693 |bibcode=2022MNRAS.512L...6D |doi=10.1093/mnrasl/slac012 |doi-access=free |access-date=20 April 2024 |archive-date=9 April 2023 |archive-url=https://web.archive.org/web/20230409170426/https://academic.oup.com/mnrasl/article-abstract/512/1/L6/6524836 |url-status=live }}</ref> However, some astronomers said that this observation might be credited to observational biases or just sheer coincidence.<ref>{{cite journal |last=Napier |first=K. J. |date=2021 |title=No Evidence for Orbital Clustering in the Extreme Trans-Neptunian Objects |journal=The Planetary Science Journal |volume=2 |issue=2 |page=59 |arxiv=2102.05601 |bibcode=2021PSJ.....2...59N |doi=10.3847/PSJ/abe53e |doi-access=free}}</ref> An alternative hypothesis has a close flyby of another star disrupting the outer Solar System.<ref>{{cite journal | title=Trajectory of the stellar flyby that shaped the outer Solar System | first1=Susanne | last1=Pfalzner | first2=Amith | last2=Govind | first3=Simon Portegies | last3=Zwart | journal=Nature Astronomy | date=September 2024 | volume=8 | issue=11 | pages=1380–1386 | doi=10.1038/s41550-024-02349-x | arxiv=2409.03342 | bibcode=2024NatAs...8.1380P }}</ref>

The Sun's gravitational field is estimated to [[Sphere of influence (astrodynamics)|dominate the gravitational forces of surrounding stars]] out to about two light-years ({{val|125,000|fmt=commas|u=AU}}). Lower estimates for the radius of the Oort cloud, by contrast, do not place it farther than {{val|50,000|fmt=commas|u=AU}}.<ref name="Encrenaz_et_al_2004">{{Cite book |last1=Encrenaz |first1=T. |author-link=Thérèse Encrenaz |title=The Solar System |last2=Bibring |first2=J. P. |last3=Blanc |first3=M. |last4=Barucci |first4=M. A. |last5=Roques |first5=F. |last6=Zarka |first6=P. H. |date=2004 |publisher=Springer |edition=3rd |page=1}}</ref> Most of the mass is orbiting in the region between 3,000 and {{val|100,000|fmt=commas|u=AU}}.<ref>{{Cite journal |last1=Torres |first1=S. |last2=Cai |first2=M. X. |last3=Brown |first3=A. G. A. |last4=Portegies Zwart |first4=S. |date=September 2019 |title=Galactic tide and local stellar perturbations on the Oort cloud: creation of interstellar comets |journal=Astronomy & Astrophysics |volume=629 |page=13 |arxiv=1906.10617 |bibcode=2019A&A...629A.139T |doi=10.1051/0004-6361/201935330 |s2cid=195584070 |id=A139}}</ref> The furthest known objects, such as [[Comet West]], have aphelia around {{val|70,000|fmt=commas|u=AU}} from the Sun.<ref>{{Cite web |last=Norman |first=Neil |date=May 2020 |title=10 great comets of recent times |url=https://www.skyatnightmagazine.com/space-science/greatest-comets-of-recent-times |url-status=live |archive-url=https://web.archive.org/web/20220125042109/https://www.skyatnightmagazine.com/space-science/greatest-comets-of-recent-times |archive-date=25 January 2022 |access-date=10 April 2022 |website=[[BBC Sky at Night|BBC Sky at Night Magazine]] |language=en}}</ref> The Sun's [[Hill sphere]] with respect to the galactic nucleus, the effective range of its gravitational influence, is thought to extend up to a thousand times farther and encompasses the hypothetical Oort cloud.<ref name="Littmann">{{Cite book |last=Littmann |first=Mark |url=https://archive.org/details/planetsbeyonddis00mlit |title=Planets Beyond: Discovering the Outer Solar System |date=2004 |publisher=Courier Dover Publications |isbn=978-0-486-43602-9 |pages=[https://archive.org/details/planetsbeyonddis00mlit/page/n92 162]–163 |url-access=limited}}</ref> It was calculated by [[Gleb Alexandrovich Chebotarev|G. A. Chebotarev]] to be 230,000&nbsp;AU.<ref name=Chebotarev />

[[File:Interstellar medium annotated.jpg|thumb|center|upright=2.5|The Solar System (left) within the [[interstellar medium]], with the different regions and their distances on a [[logarithmic scale]]]]

== Celestial neighborhood ==
{{Main|List of nearest stars|List of nearest exoplanets|List of nearby stellar associations and moving groups}}
[[File:The Local Interstellar Cloud and neighboring G-cloud complex.svg|thumb|Diagram of the [[Local Interstellar Cloud]], the [[G-Cloud]] and surrounding stars. As of 2022, the precise location of the Solar System in the clouds is an open question in astronomy.<ref>{{Cite journal |last1=Swaczyna |first1=Paweł |last2=Schwadron |first2=Nathan A. |last3=Möbius |first3=Eberhard |last4=Bzowski |first4=Maciej |last5=Frisch |first5=Priscilla C. |last6=Linsky |first6=Jeffrey L. |last7=McComas |first7=David J. |last8=Rahmanifard |first8=Fatemeh |last9=Redfield |first9=Seth |last10=Winslow |first10=Réka M. |last11=Wood |first11=Brian E. |last12=Zank |first12=Gary P. |date=1 October 2022 |title=Mixing Interstellar Clouds Surrounding the Sun |journal=[[The Astrophysical Journal Letters]] |volume=937 |issue=2 |pages=L32:1–2 |arxiv=2209.09927 |bibcode=2022ApJ...937L..32S |doi=10.3847/2041-8213/ac9120 |issn=2041-8205 |doi-access=free}}</ref>]]

Within 10&nbsp;light-years of the Sun there are relatively few stars, the closest being the triple star system [[Alpha Centauri]], which is about 4.4&nbsp;light-years away and may be in the Local Bubble's [[G-Cloud]].<ref>{{Cite journal |last1=Linsky |first1=Jeffrey L. |last2=Redfield |first2=Seth |last3=Tilipman |first3=Dennis |date=November 2019 |title=The Interface between the Outer Heliosphere and the Inner Local ISM: Morphology of the Local Interstellar Cloud, Its Hydrogen Hole, Strömgren Shells, and 60Fe Accretion |journal=[[The Astrophysical Journal]] |volume=886 |issue=1 |page=19 |arxiv=1910.01243 |bibcode=2019ApJ...886...41L |doi=10.3847/1538-4357/ab498a |s2cid=203642080 |id=41 |doi-access=free}}</ref> Alpha Centauri A and B are a closely tied pair of [[Solar analog|Sun-like stars]], whereas the closest star to the Sun, the small [[red dwarf]] [[Proxima Centauri]], orbits the pair at a distance of 0.2&nbsp;light-years. In 2016, a potentially habitable [[exoplanet]] was found to be orbiting Proxima Centauri, called [[Proxima Centauri b]], the closest confirmed exoplanet to the Sun.<ref name="proxima b discovery paper">{{Cite journal |last1=Anglada-Escudé |first1=Guillem |last2=Amado |first2=Pedro J. |last3=Barnes |first3=John |last4=Berdiñas |first4=Zaira M. |last5=Butler |first5=R. Paul |last6=Coleman |first6=Gavin A. L. |last7=de la Cueva |first7=Ignacio |last8=Dreizler |first8=Stefan |last9=Endl |first9=Michael |last10=Giesers |first10=Benjamin |last11=Jeffers |first11=Sandra V. |last12=Jenkins |first12=James S. |last13=Jones |first13=Hugh R. A. |last14=Kiraga |first14=Marcin |last15=Kürster |first15=Martin |display-authors=3 |year=2016 |title=A terrestrial planet candidate in a temperate orbit around Proxima Centauri |url=https://www.nature.com/articles/nature19106 |journal=[[Nature (journal)|Nature]] |volume=536 |issue=7617 |pages=437–440 |arxiv=1609.03449 |bibcode=2016Natur.536..437A |doi=10.1038/nature19106 |pmid=27558064 |s2cid=4451513 |last16=López-González |first16=María J. |last17=Marvin |first17=Christopher J. |last18=Morales |first18=Nicolás |last19=Morin |first19=Julien |last20=Nelson |first20=Richard P. |last21=Ortiz |first21=José L. |last22=Ofir |first22=Aviv |last23=Paardekooper |first23=Sijme-Jan |last24=Reiners |first24=Ansgar |last25=Rodríguez |first25=Eloy |last26=Rodríguez-López |first26=Cristina |last27=Sarmiento |first27=Luis F. |last28=Strachan |first28=John P. |last29=Tsapras |first29=Yiannis |last30=Tuomi |first30=Mikko |first31=Mathias |last31=Zechmeister}}</ref>

The Solar System is surrounded by the [[Local Interstellar Cloud]], although it is not clear if it is embedded in the Local Interstellar Cloud or if it lies just outside the cloud's edge.<ref name=":1">{{Cite journal |last1=Linsky |first1=Jeffrey L. |last2=Redfield |first2=Seth |last3=Tilipman |first3=Dennis |date=20 November 2019 |title=The Interface between the Outer Heliosphere and the Inner Local ISM: Morphology of the Local Interstellar Cloud, Its Hydrogen Hole, Strömgren Shells, and 60 Fe Accretion* |journal=[[The Astrophysical Journal]] |volume=886 |issue=1 |page=41 |arxiv=1910.01243 |bibcode=2019ApJ...886...41L |doi=10.3847/1538-4357/ab498a |issn=0004-637X |s2cid=203642080 |doi-access=free}}</ref> Multiple other [[interstellar cloud]]s exist in the region within 300&nbsp;light-years of the Sun, known as the [[Local Bubble]].<ref name=":1" /> The latter feature is an hourglass-shaped cavity or [[superbubble]] in the interstellar medium roughly 300&nbsp;light-years across. The bubble is suffused with high-temperature plasma, suggesting that it may be the product of several recent supernovae.<ref>{{Cite journal |last1=Zucker |first1=Catherine |last2=Goodman |first2=Alyssa A. |author-link2=Alyssa A. Goodman |last3=Alves |first3=João |last4=Bialy |first4=Shmuel |last5=Foley |first5=Michael |last6=Speagle |first6=Joshua S. |last7=Großschedl |first7=Josefa |last8=Finkbeiner |first8=Douglas P. |last9=Burkert |first9=Andreas |last10=Khimey |first10=Diana |last11=Swiggum |first11=Cameren |display-authors=3 |date=January 2022 |title=Star formation near the Sun is driven by expansion of the Local Bubble |url=https://www.nature.com/articles/s41586-021-04286-5 |journal=[[Nature (journal)|Nature]] |language=en |volume=601 |issue=7893 |pages=334–337 |arxiv=2201.05124 |bibcode=2022Natur.601..334Z |doi=10.1038/s41586-021-04286-5 |issn=1476-4687 |pmid=35022612 |s2cid=245906333}}</ref>

The Local Bubble is a small superbubble compared to the neighboring wider [[Radcliffe Wave]] and ''Split'' linear structures (formerly [[Gould Belt]]), each of which are some thousands of light-years in length.<ref name="Alves Zucker Goodman Speagle 2020">{{Cite journal |last1=Alves |first1=João |last2=Zucker |first2=Catherine |last3=Goodman |first3=Alyssa A. |last4=Speagle |first4=Joshua S. |last5=Meingast |first5=Stefan |last6=Robitaille |first6=Thomas |last7=Finkbeiner |first7=Douglas P. |last8=Schlafly |first8=Edward F. |last9=Green |first9=Gregory M. |date=23 January 2020 |title=A Galactic-scale gas wave in the Solar Neighborhood |journal=[[Nature (journal)|Nature]] |volume=578 |issue=7794 |pages=237–239 |arxiv=2001.08748v1 |bibcode=2020Natur.578..237A |doi=10.1038/s41586-019-1874-z |pmid=31910431 |s2cid=210086520}}</ref> All these structures are part of the [[Orion Arm]], which contains most of the stars in the Milky Way that are visible to the unaided eye.<ref>{{Cite journal |last1=McKee |first1=Christopher F. |last2=Parravano |first2=Antonio |last3=Hollenbach |first3=David J. |date=November 2015 |title=Stars, Gas, and Dark Matter in the Solar Neighborhood |journal=[[The Astrophysical Journal]] |volume=814 |issue=1 |pages=24 |arxiv=1509.05334 |bibcode=2015ApJ...814...13M |doi=10.1088/0004-637X/814/1/13 |s2cid=54224451 |id=13}}</ref>

Groups of stars form together in [[star cluster]]s, before dissolving into co-moving associations. A prominent grouping that is visible to the naked eye is the [[Ursa Major moving group]], which is around 80 light-years away within the Local Bubble. The nearest star cluster is [[Hyades (star cluster)|Hyades]], which lies at the edge of the Local Bubble. The closest star-forming regions are the [[Corona Australis Molecular Cloud]], the [[Rho Ophiuchi cloud complex]] and the [[Taurus molecular cloud]]; the latter lies just beyond the Local Bubble and is part of the Radcliffe wave.<ref>{{Cite journal |last1=Alves |first1=João |last2=Zucker |first2=Catherine |last3=Goodman |first3=Alyssa A. |author-link3=Alyssa A. Goodman |last4=Speagle |first4=Joshua S. |last5=Meingast |first5=Stefan |last6=Robitaille |first6=Thomas |last7=Finkbeiner |first7=Douglas P. |last8=Schlafly |first8=Edward F. |last9=Green |first9=Gregory M. |display-authors=3 |year=2020 |title=A Galactic-scale gas wave in the solar neighborhood |journal=[[Nature (journal)|Nature]] |volume=578 |issue=7794 |pages=237–239 |arxiv=2001.08748 |bibcode=2020Natur.578..237A |doi=10.1038/s41586-019-1874-z |pmid=31910431 |s2cid=210086520}}</ref>

Stellar flybys that pass within {{Convert|0.25|pc|ly|1|abbr=off|disp=out}} of the Sun occur roughly once every 100,000&nbsp;years. The [[List of nearest stars#Distant future and past encounters|closest well-measured approach]] was [[Scholz's Star]], which approached to ~{{val|50,000|fmt=commas|u=AU}} of the Sun some ~70&nbsp;thousands years ago, likely passing through the outer Oort cloud.<ref>{{Cite journal |last1=Mamajek |first1=Eric E. |last2=Barenfeld |first2=Scott A. |last3=Ivanov |first3=Valentin D. |last4=Kniazev |first4=Alexei Y. |last5=Väisänen |first5=Petri |last6=Beletsky |first6=Yuri |last7=Boffin |first7=Henri M. J. |date=February 2015 |title=The Closest Known Flyby of a Star to the Solar System |journal=[[The Astrophysical Journal Letters]] |volume=800 |issue=1 |page=4 |arxiv=1502.04655 |bibcode=2015ApJ...800L..17M |doi=10.1088/2041-8205/800/1/L17 |s2cid=40618530 |id=L17}}</ref> There is a 1% chance every billion years that a star will pass within {{val|100|u=AU}} of the Sun, potentially disrupting the Solar System.<ref name="Raymond_et_al_2024">{{cite journal |last1=Raymond |first1=Sean N. |last2=Kaib |first2=Nathan A. |last3=Selsis |first3=Franck |last4=Bouy |first4=Herve |display-authors=1 |date=January 2024 |title=Future trajectories of the Solar System: dynamical simulations of stellar encounters within 100 au |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=527 |issue=3 |pages=6126–6138 |arxiv=2311.12171 |bibcode=2024MNRAS.527.6126R |doi=10.1093/mnras/stad3604|doi-access=free }}</ref>

== Galactic position ==
{{See also|Location of Earth|Galactic year|Orbit of the Sun}}
[[File:Milky Way side view.png|thumb|Diagram of the Milky Way, with galactic features and the relative position of the Solar System labeled.]]

The Solar System is located in the [[Milky Way]], a [[barred spiral galaxy]] with a diameter of about 100,000&nbsp;[[light-year]]s containing more than 100&nbsp;billion stars.<ref name="Lang2013">{{Cite book |last=Lang |first=Kenneth R. |url=https://books.google.com/books?id=MN-UCkUK9pcC&pg=PA264 |title=The Life and Death of Stars |date=2013 |publisher=Cambridge University Press |isbn=978-1107016385 |page=264 |access-date=8 April 2022 |archive-url=https://web.archive.org/web/20220420161220/https://www.google.com/books/edition/The_Life_and_Death_of_Stars/MN-UCkUK9pcC?gbpv=1&pg=PA264 |archive-date=20 April 2022 |url-status=live}}</ref> The Sun is part of one of the Milky Way's outer spiral arms, known as the [[Orion–Cygnus Arm]] or Local Spur.<ref>{{Cite journal |last1=Drimmel |first1=R. |last2=Spergel |first2=D. N. |date=2001 |title=Three Dimensional Structure of the Milky Way Disk |journal=[[The Astrophysical Journal]] |volume=556 |issue=1 |pages=181–202 |arxiv=astro-ph/0101259 |bibcode=2001ApJ...556..181D |doi=10.1086/321556 |s2cid=15757160}}</ref><ref>{{Cite journal |last=Gerhard |first=O. |date=2011 |title=Pattern speeds in the Milky Way |journal=Memorie della Societa Astronomica Italiana, Supplementi |volume=18 |page=185 |arxiv=1003.2489 |bibcode=2011MSAIS..18..185G}}</ref> It is a member of the [[thin disk]] population of stars orbiting close to the galactic plane.<ref>{{cite journal | title=The formation of the Oort cloud in open cluster environments | last1=Kaib | first1=Nathan A. | last2=Quinn | first2=Thomas | journal=Icarus | date=September 2008 | volume=197 | issue=1 | pages=221–238 | doi=10.1016/j.icarus.2008.03.020 | arxiv=0707.4515 | bibcode=2008Icar..197..221K }}</ref>

Its speed around the center of the Milky Way is about 220&nbsp;km/s, so that it completes one revolution every 240&nbsp;million years.<ref name="Lang2013"/> This revolution is known as the Solar System's [[galactic year]].<ref>{{Cite web |last=Leong |first=Stacy |date=2002 |title=Period of the Sun's Orbit around the Galaxy (Cosmic Year) |url=http://hypertextbook.com/facts/2002/StacyLeong.shtml |url-status=live |archive-url=https://web.archive.org/web/20190107010909/https://hypertextbook.com/facts/2002/StacyLeong.shtml |archive-date=7 January 2019 |access-date=2 April 2007 |website=The Physics Factbook}}</ref> The [[solar apex]], the direction of the Sun's path through interstellar space, is near the constellation [[Hercules (constellation)|Hercules]] in the direction of the current location of the bright star [[Vega]].<ref>{{Cite book |last=Greiner |first=Walter |url=https://www.worldcat.org/oclc/56727455 |title=Classical Mechanics: Point particles and relativity |date=2004 |publisher=Springer |isbn=978-0-387-21851-9 |location=New York |page=323 |oclc=56727455 |access-date=29 March 2022 |archive-url=https://web.archive.org/web/20220420161222/https://www.worldcat.org/title/classical-mechanics-point-particles-and-relativity/oclc/56727455 |archive-date=20 April 2022 |url-status=live}}</ref> The plane of the ecliptic lies at an angle of about 60° to the [[galactic plane]].{{Refn |group=lower-alpha |name=angle |1=If <math>\psi</math> is the angle between the [[Ecliptic pole|north pole of the ecliptic]] and the north [[galactic pole]] then:
<br />{{Big|1=<math>\cos\psi=\cos(\beta_g)\cos(\beta_e)\cos(\alpha_g-\alpha_e)+\sin(\beta_g)\sin(\beta_e)</math>}}<br />
where <math>\beta_g</math> = 27° 07′ 42.01″ and <math>\alpha_g</math> = 12h 51m 26.282s are the declination and right ascension of the north galactic pole,<ref>{{Cite journal |last1=Reid |first1=M. J. |last2=Brunthaler |first2=A. |date=2004 |title=The Proper Motion of Sagittarius A* |journal=[[The Astrophysical Journal]] |volume=616 |issue=2 |pages=872–884 |arxiv=astro-ph/0408107 |bibcode=2004ApJ...616..872R |doi=10.1086/424960 |s2cid=16568545}}</ref> whereas <math>\beta_e</math> = 66° 33′ 38.6″ and <math>\alpha_e</math> = 18h 0m 00s are those for the north pole of the ecliptic. (Both pairs of coordinates are for [[J2000]] epoch.) The result of the calculation is 60.19°.}}

The Sun follows a nearly circular orbit around the [[Galactic Center]] (where the [[supermassive black hole]] [[Sagittarius A*]] resides) at a distance of 26,660&nbsp;light-years,<ref>{{Cite journal |last1=Abuter |first1=R. |last2=Amorim |first2=A. |last3=Bauböck |first3=M. |last4=Berger |first4=J. P. |last5=Bonnet |first5=H. |last6=Brandner |first6=W. |last7=Clénet |first7=Y. |last8=Coudé du Foresto |first8=V. |last9=de Zeeuw |first9=P. T. |last10=Dexter |first10=J. |display-authors=6 |date=May 2019 |title=A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty |url=https://www.aanda.org/10.1051/0004-6361/201935656 |url-status=live |journal=Astronomy & Astrophysics |volume=625 |page=L10 |arxiv=1904.05721 |bibcode=2019A&A...625L..10G |doi=10.1051/0004-6361/201935656 |issn=0004-6361 |s2cid=119190574 |archive-url=https://web.archive.org/web/20220420161243/https://www.aanda.org/articles/aa/full_html/2019/05/aa35656-19/aa35656-19.html |archive-date=20 April 2022 |access-date=1 April 2022}}</ref> orbiting at roughly the same speed as that of the spiral arms.<ref name="astrobiology">{{Cite web |last=Mullen |first=Leslie |date=18 May 2001 |title=Galactic Habitable Zones |url=http://www.astrobio.net/news-exclusive/galactic-habitable-zones |url-status=live |archive-url=https://web.archive.org/web/20110807024530/http://www.astrobio.net/exclusive/139/galactic-habitable-zones |archive-date=7 August 2011 |access-date=1 June 2020 |website=Astrobiology Magazine}}</ref> If it orbited close to the center, gravitational tugs from nearby stars could perturb bodies in the [[#Oort cloud|Oort cloud]] and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. In this scenario, the intense radiation of the Galactic Center could interfere with the development of complex life.<ref name="astrobiology" />

The Solar System's location in the Milky Way is a factor in the [[evolutionary history of life]] on Earth. Spiral arms are home to a far larger concentration of [[supernova]]e, gravitational instabilities, and radiation that could disrupt the Solar System, but since Earth stays in the Local Spur and therefore does not pass frequently through spiral arms, this has given Earth long periods of stability for life to evolve.<ref name="astrobiology" /> However, according to the controversial [[Shiva hypothesis]], the changing position of the Solar System relative to other parts of the Milky Way could explain periodic [[extinction events]] on Earth.<ref>{{Cite journal |last=Bailer-Jones |first=C. A. L. |date=1 July 2009 |title=The evidence for and against astronomical impacts on climate change and mass extinctions: a review |url=https://ui.adsabs.harvard.edu/abs/2009IJAsB...8..213B |url-status=live |journal=International Journal of Astrobiology |volume=8 |issue=3 |pages=213–219 |arxiv=0905.3919 |bibcode=2009IJAsB...8..213B |doi=10.1017/S147355040999005X |s2cid=2028999 |archive-url=https://web.archive.org/web/20220401231355/https://ui.adsabs.harvard.edu/abs/2009IJAsB...8..213B |archive-date=1 April 2022 |access-date=1 April 2022}}</ref><ref>{{Cite journal |last=Racki |first=Grzegorz |date=December 2012 |title=The Alvarez Impact Theory of Mass Extinction; Limits to its Applicability and the "Great Expectations Syndrome" |url=https://www.app.pan.pl/article/item/app20110058.html |url-status=live |journal=Acta Palaeontologica Polonica |language=en |volume=57 |issue=4 |pages=681–702 |doi=10.4202/app.2011.0058 |issn=0567-7920 |s2cid=54021858 |archive-url=https://web.archive.org/web/20220401214314/https://www.app.pan.pl/article/item/app20110058.html |archive-date=1 April 2022 |access-date=1 April 2022 |doi-access=free |hdl-access=free |hdl=20.500.12128/534}}</ref>

== Discovery and exploration ==
{{Main|Discovery and exploration of the Solar System}}
[[File:Apparent retrograde motion of Mars in 2003.gif|thumb|The motion of 'lights' moving across the sky is the basis of the classical definition of planets: wandering stars.]]
Humanity's knowledge of the Solar System has grown incrementally over the centuries. Up to the [[Late Middle Ages]]–[[Renaissance]], astronomers from Europe to India believed Earth to [[Geocentric model|be stationary at the center]] of the universe<ref>{{Cite book |last=Orrell |first=David |url=https://books.google.com/books?id=mNMsa18vTpsC&pg=PA25 |title=Truth Or Beauty: Science and the Quest for Order |date=2012 |publisher=Yale University Press |isbn=978-0300186611 |pages=25–27 |access-date=13 May 2022 |archive-url=https://web.archive.org/web/20220730084322/https://www.google.com/books/edition/Truth_Or_Beauty/mNMsa18vTpsC?gbpv=1&pg=PA25 |archive-date=30 July 2022 |url-status=live}}</ref> and categorically different from the divine or ethereal objects that moved through the sky. Although the [[Ancient Greece|Greek]] philosopher [[Aristarchus of Samos]] had speculated on a [[heliocentric]] reordering of the cosmos, [[Nicolaus Copernicus]] was the first person known to have developed [[Copernican heliocentrism|a mathematically predictive heliocentric system]].<ref>{{Cite magazine |last=Rufus |first=W. C. |date=1923 |title=The astronomical system of Copernicus |magazine=[[Popular Astronomy (US magazine)|Popular Astronomy]] |volume=31 |page=510 |bibcode=1923PA.....31..510R}}</ref><ref>{{Cite book |last=Weinert |first=Friedel |url=https://archive.org/details/copernicusdarwin00wein |title=Copernicus, Darwin, & Freud: revolutions in the history and philosophy of science |date=2009 |publisher=[[Wiley-Blackwell]] |isbn=978-1-4051-8183-9 |page=[https://archive.org/details/copernicusdarwin00wein/page/n29 21] |url-access=limited}}</ref>

Heliocentrism did not triumph immediately over geocentrism, but the work of Copernicus had its champions, notably [[Johannes Kepler]]. Using a heliocentric model that improved upon Copernicus by allowing orbits to be elliptical, and the precise observational data of [[Tycho Brahe]], Kepler produced the ''[[Rudolphine Tables]]'', which enabled accurate computations of the positions of the then-known planets. [[Pierre Gassendi]] used them to predict a [[transit of Mercury]] in 1631, and [[Jeremiah Horrocks]] did the same for a [[transit of Venus]] in 1639. This provided a strong vindication of heliocentrism and Kepler's elliptical orbits.<ref>{{Cite book |last=LoLordo |first=Antonia |url=https://www.worldcat.org/oclc/182818133 |title=Pierre Gassendi and the Birth of Early Modern Philosophy |date=2007 |publisher=Cambridge University Press |isbn=978-0-511-34982-9 |location=New York |pages=12, 27 |oclc=182818133 |access-date=1 April 2022 |archive-url=https://web.archive.org/web/20220420161223/https://www.worldcat.org/title/pierre-gassendi-and-the-birth-of-early-modern-philosophy/oclc/182818133 |archive-date=20 April 2022 |url-status=live}}</ref><ref>{{Cite journal |last1=Athreya |first1=A. |last2=Gingerich |first2=O. |date=December 1996 |title=An Analysis of Kepler's Rudolphine Tables and Implications for the Reception of His Physical Astronomy |journal=Bulletin of the American Astronomical Society |volume=28 |issue=4 |page=1305 |bibcode=1996AAS...189.2404A}}<!--|accessdate=26 December 2013--></ref>

In the 17th century, [[Galileo Galilei|Galileo]] publicized the use of the telescope in astronomy; he and [[Simon Marius]] independently discovered that Jupiter had four satellites in orbit around it.<ref>{{Cite journal |last=Pasachoff |first=Jay M. |date=May 2015 |title=Simon Marius's Mundus Iovialis: 400th Anniversary in Galileo's Shadow |url=http://journals.sagepub.com/doi/10.1177/0021828615585493 |url-status=live |journal=Journal for the History of Astronomy |language=en |volume=46 |issue=2 |pages=218–234 |bibcode=2015JHA....46..218P |doi=10.1177/0021828615585493 |issn=0021-8286 |s2cid=120470649 |archive-url=https://web.archive.org/web/20211127213209/https://journals.sagepub.com/doi/10.1177/0021828615585493 |archive-date=27 November 2021 |access-date=1 April 2022}}</ref> [[Christiaan Huygens]] followed on from these observations by discovering Saturn's moon [[Titan (moon)|Titan]] and the shape of the [[rings of Saturn]].<ref>{{Cite web |date=8 December 2012 |title=Christiaan Huygens: Discoverer of Titan |url=https://www.esa.int/About_Us/ESA_history/Christiaan_Huygens_Discoverer_of_Titan |url-status=live |archive-url=https://web.archive.org/web/20191206001920/http://www.esa.int/About_Us/ESA_history/Christiaan_Huygens_Discoverer_of_Titan |archive-date=6 December 2019 |access-date=27 October 2010 |website=ESA Space Science |publisher=The European Space Agency}}</ref> In 1677, [[Edmond Halley]] observed a transit of Mercury across the Sun, leading him to realize that observations of the [[solar parallax]] of a planet (more ideally using the transit of Venus) could be used to [[Trigonometry|trigonometrically]] determine the distances between Earth, [[Venus]], and the Sun.<ref>{{Cite conference |last=Chapman |first=Allan |date=April 2005 |editor-last=Kurtz |editor-first=D. W. |title=Jeremiah Horrocks, William Crabtree, and the Lancashire observations of the transit of Venus of 1639 |conference=Transits of Venus: New Views of the Solar System and Galaxy, Proceedings of IAU Colloquium #196, held 7–11 June 2004 in Preston, U.K. |publisher=Cambridge University Press |publication-place=Cambridge |volume=2004 |pages=3–26 |bibcode=2005tvnv.conf....3C |doi=10.1017/S1743921305001225 |doi-access=free |journal=Proceedings of the International Astronomical Union}}</ref> Halley's friend [[Isaac Newton]], in his magisterial ''[[Philosophiæ Naturalis Principia Mathematica|Principia Mathematica]]'' of 1687, demonstrated that celestial bodies are not quintessentially different from Earthly ones: the same [[Newton's laws of motion|laws of motion]] and of [[Newton's law of universal gravitation|gravity]] apply on Earth and in the skies.<ref name=":0"/>{{Rp|page=142}}
[[File:The Solar System, with the orbits of 5 remarkable comets. LOC 2013593161 (cropped).jpg|thumb|Solar system diagram by [[Emanuel Bowen]] in 1747, when neither Uranus, Neptune, nor the asteroid belts had yet been discovered. Orbits of planets are to scale, but the orbits of moons and the sizes of bodies are not.]]
The term "Solar System" entered the English language by 1704, when [[John Locke]] used it to refer to the Sun, planets, and comets.<ref>See, for example:

*{{Cite web |title=solar |url=https://www.etymonline.com/word/solar |url-status=live |archive-url=https://web.archive.org/web/20220318002833/https://www.etymonline.com/word/solar |archive-date=18 March 2022 |access-date=17 March 2022 |website=[[Online Etymology Dictionary]]}}
*{{Cite OED|solar system}}
*{{Cite book |last=Locke |first=John |url=https://books.google.com/books?id=Ni9bAAAAcAAJ |title=Elements of Natural Philosophy ... To which are added. Some Thoughts concerning Reading and Study for a Gentleman. By the same author. With prefatory remarks by P. Des Maizeaux |date=1754 |publisher=R. Taylor |page=8 |language=en |author-link=John Locke |orig-date=1720 |access-date=18 March 2022 |archive-date=18 March 2022 |archive-url=https://web.archive.org/web/20220318005707/https://books.google.com/books?id=Ni9bAAAAcAAJ&newbks=0 |url-status=live }} Posthumous publication.</ref> In 1705, Halley realized that repeated sightings of [[Halley's Comet|a comet]] were of the same object, returning regularly once every 75–76&nbsp;years. This was the first evidence that anything other than the planets repeatedly orbited the Sun,<ref>{{Cite book |last1=Festou |first1=M. C. |title=Comets II |last2=Keller |first2=H. U. |last3=Weaver |first3=H. A. |date=2004 |publisher=University of Arizona Press |isbn=978-0816524501 |publication-place=Tucson |pages=3–16 |chapter=A brief conceptual history of cometary science |bibcode=2004come.book....3F |access-date=7 April 2022 |chapter-url=https://books.google.com/books?id=ehA8EAAAQBAJ&pg=PA4 |archive-url=https://web.archive.org/web/20220420161222/https://www.google.com/books/edition/Comets_II/ehA8EAAAQBAJ?gbpv=1&pg=PA4 |archive-date=20 April 2022 |url-status=live}}</ref> though [[Seneca the Younger|Seneca]] had theorized this about comets in the 1st century.<ref>{{Cite book |last1=Sagan |first1=Carl |url=https://books.google.com/books?id=LhkoowKFaTsC |title=Comet |last2=Druyan |first2=Ann |publisher=Random House |year=1997 |isbn=978-0-3078-0105-0 |location=New York |pages=26–27, 37–38 |author-link=Carl Sagan |author-link2=Ann Druyan |access-date=28 June 2021 |archive-url=https://web.archive.org/web/20210615020250/https://books.google.com/books?id=LhkoowKFaTsC |archive-date=15 June 2021 |url-status=live}}</ref> Careful observations of the 1769 transit of Venus allowed astronomers to calculate the average Earth–Sun distance as {{Convert|93726900|mi|km}}, only 0.8% greater than the modern value.<ref>{{Cite journal |last=Teets |first=Donald |date=December 2003 |title=Transits of Venus and the Astronomical Unit |url=http://www.maa.org/sites/default/files/pdf/pubs/mm_dec03-Venus.pdf |url-status=live |journal=Mathematics Magazine |volume=76 |pages=335–348 |doi=10.1080/0025570X.2003.11953207 |jstor=3654879 |s2cid=54867823 |archive-url=https://web.archive.org/web/20220203080207/https://www.maa.org/sites/default/files/pdf/pubs/mm_dec03-Venus.pdf |archive-date=3 February 2022 |access-date=3 April 2022 |number=5}}</ref>

[[Uranus]], having occasionally been observed since 1690 and possibly from antiquity, was recognized to be a planet orbiting beyond Saturn by 1783.<ref>{{Cite journal |last=Bourtembourg |first=René |date=2013 |title=Was Uranus Observed by Hipparchos? |journal=Journal for the History of Astronomy |volume=44 |issue=4 |pages=377–387 |bibcode=2013JHA....44..377B |doi=10.1177/002182861304400401 |s2cid=122482074}}</ref> In 1838, [[Friedrich Bessel]] successfully measured a [[stellar parallax]], an apparent shift in the position of a star created by Earth's motion around the Sun, providing the first direct, experimental proof of heliocentrism.<ref>{{Cite book |last=Di Bari |first=Pasquale |url=https://books.google.com/books?id=hPm7DwAAQBAJ&pg=PA4 |title=Cosmology and the Early Universe |date=2018 |publisher=CRC Press |isbn=978-1351020138 |pages=3–4}}</ref> [[Neptune]] was identified as a planet some years later, in 1846, thanks to its gravitational pull causing a slight but detectable variation in the orbit of Uranus.<ref>{{Cite journal |last1=Bhatnagar |first1=Siddharth |last2=Vyasanakere |first2=Jayanth P. |last3=Murthy |first3=Jayant |date=May 2021 |title=A geometric method to locate Neptune |url=https://aapt.scitation.org/doi/10.1119/10.0003349 |url-status=live |journal=American Journal of Physics |language=en |volume=89 |issue=5 |pages=454–458 |arxiv=2102.04248 |bibcode=2021AmJPh..89..454B |doi=10.1119/10.0003349 |issn=0002-9505 |s2cid=231846880 |archive-url=https://web.archive.org/web/20211129125826/https://aapt.scitation.org/doi/10.1119/10.0003349 |archive-date=29 November 2021 |access-date=1 April 2022}}</ref> [[Perihelion precession of Mercury|Mercury's orbital anomaly]] observations led to searches for [[Vulcan (hypothetical planet)|Vulcan]], a planet interior of Mercury, but these attempts were quashed with [[Albert Einstein]]'s theory of [[general relativity]] in 1915.<ref name="Clemence">{{cite journal |last=Clemence |first=G. M. |date=1947 |title=The Relativity Effect in Planetary Motions |journal=Reviews of Modern Physics |volume=19 |issue=4 |pages=361–364 |bibcode=1947RvMP...19..361C |doi=10.1103/RevModPhys.19.361}} [http://www.mathpages.com/rr/s6-02/6-02.htm (math)]</ref>

In the 20th century, humans began their space exploration around the Solar System, starting with placing [[Space telescope|telescopes in space]] since the 1960s.<ref>{{Cite web |last=Garner |first=Rob |date=10 December 2018 |title=50th Anniversary of OAO 2: NASA's 1st Successful Stellar Observatory |url=http://www.nasa.gov/feature/goddard/2018/nasa-s-first-stellar-observatory-oao-2-turns-50 |url-status=live |archive-url=https://web.archive.org/web/20211229231948/https://www.nasa.gov/feature/goddard/2018/nasa-s-first-stellar-observatory-oao-2-turns-50 |archive-date=29 December 2021 |access-date=20 April 2022 |website=NASA}}</ref> By 1989, all eight planets have been visited by space probes.<ref name="FactSheet">{{cite web |title=Fact Sheet |url=https://voyager.jpl.nasa.gov/news/factsheet.html |url-status=live |archive-url=https://web.archive.org/web/20161129230752/http://voyager.jpl.nasa.gov/news/factsheet.html |archive-date=29 November 2016 |access-date=3 March 2016 |publisher=JPL}}</ref> Probes have returned samples from comets<ref>{{Cite magazine |last=Woo |first=Marcus |date=20 November 2014 |title=This Is What It Sounded Like When We Landed on a Comet |url=https://www.wired.com/2014/11/sounded-like-landed-comet |archive-url=https://web.archive.org/web/20141123021050/https://www.wired.com/2014/11/sounded-like-landed-comet |archive-date=23 November 2014 |access-date=20 April 2022 |magazine=Wired}}</ref> and asteroids,<ref>{{Cite web |last=Marks |first=Paul |date=3 December 2014 |title=Hayabusa 2 probe begins journey to land on an asteroid |url=https://www.newscientist.com/article/dn26650-hayabusa-2-probe-begins-journey-to-land-on-an-asteroid |url-status=live |archive-url=https://web.archive.org/web/20220211062123/https://www.newscientist.com/article/dn26650-hayabusa-2-probe-begins-journey-to-land-on-an-asteroid |archive-date=11 February 2022 |access-date=20 April 2022 |website=New Scientist |language=en-US}}</ref> as well as flown through the [[Sun's corona]]<ref>{{Cite web |date=14 December 2021 |title=NASA's Parker Solar Probe becomes first spacecraft to 'touch' the sun |url=https://www.cnn.com/2021/12/14/world/nasa-parker-solar-probe-sun-scn/index.html |url-status=live |archive-url=https://web.archive.org/web/20211214235239/https://www.cnn.com/2021/12/14/world/nasa-parker-solar-probe-sun-scn/index.html |archive-date=14 December 2021 |access-date=15 December 2021 |website=CNN}}</ref> and visited two dwarf planets ([[Pluto]] and [[Ceres (dwarf planet)|Ceres]]).<ref>{{Cite news |last1=Corum |first1=Jonathan |last2=Gröndahl |first2=Mika |last3=Parshina-Kottas |first3=Yuliya |date=13 July 2015 |title=New Horizons' Pluto Flyby |url=https://www.nytimes.com/interactive/2015/07/14/science/space/pluto-flyby.html,%20https://www.nytimes.com/interactive/2015/07/14/science/space/pluto-flyby.html |access-date=20 April 2022 |work=The New York Times |language=en-US |issn=0362-4331}}</ref><ref name="NASA-20180907">{{cite web |last1=McCartney |first1=Gretchen |last2=Brown |first2=Dwayne |last3=Wendel |first3=JoAnna |date=7 September 2018 |title=Legacy of NASA's Dawn, Near the End of its Mission |url=https://www.jpl.nasa.gov/news/news.php?feature=7231 |access-date=8 September 2018 |work=[[NASA]]}}</ref> To save on fuel, some space missions make use of [[Gravity assist|gravity assist maneuvers]], such as the two [[Voyager program|''Voyager'' probes]] accelerating when flying by planets in the outer Solar System<ref name=":7">{{Cite web |title=Basics of Spaceflight: A Gravity Assist Primer |url=https://science.nasa.gov/learn/basics-of-space-flight/primer/ |access-date=2 May 2024 |website=science.nasa.gov}}</ref> and the [[Parker Solar Probe]] decelerating closer towards the Sun after its flyby of Venus.<ref>{{Cite web |date=4 October 2018 |title=Parker Solar Probe Changed the Game Before it Even Launched - NASA |url=https://www.nasa.gov/solar-system/parker-solar-probe-changed-the-game-before-it-even-launched/ |access-date=2 May 2024 |language=en-US}}</ref>

Humans have landed on the Moon during the [[Apollo program]] in the 1960s and 1970s<ref>{{Cite book |url=https://archive.org/details/guinnessworldrec00vari/page/13 |title=Guinness World Records 2010 |publisher=[[Bantam Books]] |year=2010 |isbn=978-0-553-59337-2 |editor-last=Glenday |editor-first=Craig |editor-link=Craig Glenday |location=New York}}</ref> and will return to the Moon in the 2020s with the [[Artemis program]].<ref name="sn-20230313">{{cite web |last=Foust |first=Jeff |date=13 March 2023 |title=NASA planning to spend up to $1 billion on space station deorbit module |url=https://spacenews.com/nasa-planning-to-spend-up-to-1-billion-on-space-station-deorbit-module/ |access-date=13 March 2023 |work=[[SpaceNews]]}}</ref> Discoveries in the 20th and 21st century has prompted the [[Definition of planet|redefinition of the term ''planet'']] in 2006, hence the demotion of Pluto to a dwarf planet,<ref name="NYT-20220118">{{cite news |last=Chang |first=Kenneth |date=18 January 2022 |title=Quiz - Is Pluto A Planet? - Who doesn't love Pluto? It shares a name with the Roman god of the underworld and a Disney dog. But is it a planet? - Interactive |url=https://www.nytimes.com/interactive/2022/science/is-pluto-a-planet.html |accessdate=18 January 2022 |work=[[The New York Times]]}}</ref> and further interest in [[trans-Neptunian object]]s.<ref name=":02">{{cite web |last=Spaceflight |first=Leonard David |date=9 January 2019 |title=A Wild 'Interstellar Probe' Mission Idea Is Gaining Momentum |url=https://www.space.com/42935-nasa-interstellar-probe-mission-idea.html |access-date=23 September 2019 |website=Space.com |language=en}}</ref>

== See also ==
{{Portal|Solar system|Outer space|Astronomy
}}
* [[Interplanetary spaceflight]]
* [[Lists of geological features of the Solar System]]
* [[List of gravitationally rounded objects of the Solar System]]
* [[List of Solar System extremes]]
* [[List of Solar System objects by size]]
* [[Outline of the Solar System]]
* {{annotated link|Planetary mnemonic}}

== Notes ==
{{Reflist|group=lower-alpha}}

== References ==

=== Data sources ===<!-- Remind that info cited to these sources need to be updated monthly -->
{{Reflist|group=D}}

=== Other sources ===
{{Reflist}}

== External links ==
{{Spoken Wikipedia|date=31 May 2021|En-Solar System-article.ogg}}
{{Library resources box
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* {{Cite EB1911|wstitle=Solar System|volume=25 |pages=157–158 |short=x}}
* [http://www.joshworth.com/a-tediously-accurate-map-of-the-solar-system/ If the Moon were only 1 Pixel: A Tediously Accurate Map of the Solar System (web based scroll map scaled to the Moon being 1 pixel)]
* [https://eyes.nasa.gov/apps/solar-system NASA's Eyes on the Solar System]
* [https://solarsystem.nasa.gov/ NASA's Solar System Exploration]
* [http://space.jpl.nasa.gov NASA's Solar System Simulator]

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