View source for Sedna (dwarf planet)

{{Short description|Distant, small body in the Solar System}}
{{Featured article}}
{{Use American English|date=August 2024}}
{{Use dmy dates|date=August 2024}}
{{Infobox planet
| minorplanet = yes
| background = #C2E0FF
| name = 90377 Sedna
| symbol = [[File:Sedna symbol (bold).svg|24px|⯲]] (mostly astrological)
| image = Sedna PRC2004-14d.jpg
| image_scale = 
| image_alt = Single fuzzy white dot with lots of background noise
| caption = Low-resolution image of Sedna by the [[Hubble Space Telescope]], March 2004
| discovery_ref = <ref name="discovery" />
| discoverer = [[Michael E. Brown|Michael Brown]]<br />[[Chad Trujillo]]<br />[[David L. Rabinowitz|David Rabinowitz]]
| discovered = 14 November 2003
| mpc_name = (90377) Sedna
| pronounced = {{IPAc-en|ˈ|s|ɛ|d|n|ə}}
| adjective = Sednian<ref name="sednian"/>
| alt_names = {{mp|2003 [[Van Biesbroeck's star catalog | VB]]|12}}
| named_after = [[Sedna (mythology)|Sedna]] ([[Inuit]] goddess of sea and marine animals)
| mp_category = [[trans-Neptunian object|TNO]]<ref name="jpldata" />{{·}}[[Detached object|detached]]<br />[[sednoid]]<ref name="DES" /> [[dwarf planet]]
| orbit_ref = <ref name="jpldata" />
| barycentric = yes
| epoch = 31 May 2020 ([[Julian day|JD]] 2458900.5)
| uncertainty = 2
| observation_arc = 30 years
| earliest_precovery_date = 2001-09-26
| semimajor = {{convert|506|AU|e9km|abbr=unit|sigfig=2}}<ref name="barycenter"/> or 0.007 ly
| perihelion = {{convert|76.19|AU|e9km|abbr=unit|sigfig=3}}<ref name="Perihelion2076"/><ref name="barycenter"/><ref name="AstDyS2076" />
| time_periastron = ≈ 18 July 2076<ref name="Perihelion2076"/><ref name="AstDyS2076" />
| aphelion = {{convert|937|AU|e9km|abbr=unit|lk=on|sigfig=2}}<ref name="barycenter"/><ref group=lower-alpha name=footnoteG/>
| eccentricity = 0.8496<ref name="barycenter"/>
| period = {{val|11390}} [[Julian year (astronomy)|yr]] (barycentric)<ref group=lower-alpha name=footnoteG/>
| synodic_period = 11,408 Gregorian years
| inclination = 11.9307[[degree (angle)|°]]
| asc_node = 144.248°
| arg_peri = 311.352°
| mean_anomaly = 358.117°
| mean_motion = {{Deg2DMS|0.00008020|sup=ms}} / day
| avg_speed = 1.04&nbsp;km/[[second|s]]
| dimensions = {{val|906|314|258|u=km}}<ref name="Lellouch A60">{{Cite journal |last1=Lellouch |first1=E. |last2=Santos-Sanz |first2=P. |last3=Lacerda |first3=P. |last4=Mommert |first4=M. |last5=Duffard |first5=R. |last6=Ortiz |first6=J. L. |last7=Müller |first7=T. G. |last8=Fornasier |first8=S. |last9=Stansberry |first9=J. |last10=Kiss |first10=Cs. |last11=Vilenius |first11=E. |last12=Mueller |first12=M. |last13=Peixinho |first13=N. |last14=Moreno |first14=R. |last15=Groussin |first15=O. |date=29 September 2013 |title="TNOs are Cool": A survey of the trans-Neptunian region: IX. Thermal properties of Kuiper belt objects and Centaurs from combined Herschel and Spitzer observations⋆⋆⋆ |journal=Astronomy & Astrophysics |volume=557 |pages=A60 |doi=10.1051/0004-6361/201322047 |issn=0004-6361|doi-access=free |bibcode=2013A&A...557A..60L |hdl=10316/80307 |hdl-access=free }}</ref><br />{{val|1025|135|u=km|p=>&nbsp;}}<br />(occultation chord)<ref name="Rommel2020"/>
| mass = 
| density = 
| surface_grav = 
| escape_velocity = 
| rotation = {{val|10.273|0.002}} [[Hour|h]]<br />(~18 h less likely)<ref name="Gaudi2005" />
| spectral_type = ([[Trans-Neptunian object#Colors|red]]) {{nowrap|1=B−V=1.24}}; {{nowrap|1=V−R=0.78}}<ref name="Tegler" />
| magnitude = 20.8 (opposition)<ref name="AstDys" /><br />20.5&nbsp;([[apsis|perihelic]])<ref name="Horizons2076" />
| abs_magnitude = {{val|1.83|0.05}}<ref name=herschel /><br />1.3<ref name="jpldata" />
| albedo = {{val|0.410|0.393|0.186}}<ref name="Lellouch A60">{{Cite journal |last1=Lellouch |first1=E. |last2=Santos-Sanz |first2=P. |last3=Lacerda |first3=P. |last4=Mommert |first4=M. |last5=Duffard |first5=R. |last6=Ortiz |first6=J. L. |last7=Müller |first7=T. G. |last8=Fornasier |first8=S. |last9=Stansberry |first9=J. |last10=Kiss |first10=Cs. |last11=Vilenius |first11=E. |last12=Mueller |first12=M. |last13=Peixinho |first13=N. |last14=Moreno |first14=R. |last15=Groussin |first15=O. |date=29 September 2013 |title="TNOs are Cool": A survey of the trans-Neptunian region: IX. Thermal properties of Kuiper belt objects and Centaurs from combined Herschel and Spitzer observations⋆⋆⋆ |journal=Astronomy & Astrophysics |volume=557 |pages=A60 |doi=10.1051/0004-6361/201322047 |issn=0004-6361|doi-access=free |bibcode=2013A&A...557A..60L |hdl=10316/80307 |hdl-access=free }}</ref>
| single_temperature = ≈ 12 [[Kelvin|K]]&nbsp;''(see [[list of Solar System objects in hydrostatic equilibrium#Manual calculations (unless otherwise cited)|note]])''
}}

'''Sedna''' ([[minor-planet designation]]: '''90377 Sedna''') is a [[dwarf planet]] in the outermost reaches of the [[Solar System]], orbiting the Sun far beyond the [[Neptune#Orbit_and_rotation|orbit of Neptune]]. Discovered in 2003, the frigid planetoid is one of the [[Trans-Neptunian object#Colors|reddest]] known among Solar System bodies. Detailed [[Spectroscopy|spectroscopic]] analysis has revealed Sedna's surface to be a mixture of the solid ices of [[Ice|water]] (H<sub>2</sub>O),<ref name=":1">{{Cite journal |last1=Emery |first1=J. P. |last2=Wong |first2=I. |last3=Brunetto |first3=R. |last4=Cook |first4=J. C. |last5=Pinilla-Alonso |first5=N. |last6=Stansberry |first6=J. A. |last7=Holler |first7=B. J. |last8=Grundy |first8=W. M. |last9=Protopapa |first9=S. |last10=Souza-Feliciano |first10=A. C. |last11=Fernández-Valenzuela |first11=E. |last12=Lunine |first12=J. I. |last13=Hines |first13=D. C. |date=2024-05-15 |title=A tale of 3 dwarf planets: Ices and organics on Sedna, Gonggong, and Quaoar from JWST spectroscopy |journal=Icarus |volume=414 |pages=116017 |doi=10.1016/j.icarus.2024.116017 |issn=0019-1035 |quote=Sedna’s relatively high visible-wavelength geometric albedo of 0.32 (which suggests a NIR geometric albedo close to or exceeding 1.0) indicates an ice-rich surface, despite the clear spectral signatures of complex organic molecules. |doi-access=free|bibcode=2024Icar..41416017E |arxiv=2309.15230 }}</ref> carbon dioxide (CO<sub>2</sub>), and [[Methane clathrate|ethane]] (C<sub>2</sub>H<sub>6</sub>), along with occasional sedimentary deposits of methane (CH<sub>4</sub>)-derived,<ref>{{Cite journal |last1=Zubko |first1=V. A. |last2=Sukhanov |first2=A. A. |last3=Fedyaev |first3=K. S. |last4=Koryanov |first4=V. V. |last5=Belyaev |first5=A. A. |date=2021-10-01 |title=Analysis of mission opportunities to Sedna in 2029–2034 |url=https://www.sciencedirect.com/science/article/abs/pii/S0273117721004555 |journal=Advances in Space Research |volume=68 |issue=7 |pages=2752–2775 |doi=10.1016/j.asr.2021.05.035 |arxiv=2112.13017 |bibcode=2021AdSpR..68.2752Z |issn=0273-1177 |quote=...As estimated in (Trujillo et al., 2005, Barucci et al., 2005, Emery et al., 2007, Pál et al., 2012, Trujillo and Sheppard, 2014), the object has a layer of hydrocarbon sediment produced by irradiated methane. The existence of the hydrocarbon sediment may be a reason why the Sedna’s surface is a bright red shade (Cuk, 2004, Sheppard, 2010).... |via=Elsevier Science Direct}}</ref> vividly reddish-colored organic [[tholin]]s,<ref name=":1" /> a surface chemical makeup somewhat similar to those of other [[trans-Neptunian objects]].<ref>{{Cite journal |last1=Emery |first1=J. P. |last2=Wong |first2=I. |last3=Brunetto |first3=R. |last4=Cook |first4=J. C. |last5=Pinilla-Alonso |first5=N. |last6=Stansberry |first6=J. A. |last7=Holler |first7=B. J. |last8=Grundy |first8=W. M. |last9=Protopapa |first9=S. |last10=Souza-Feliciano |first10=A. C. |last11=Fernández-Valenzuela |first11=E. |last12=Lunine |first12=J. I. |last13=Hines |first13=D. C. |date=2024-05-15 |title=A tale of 3 dwarf planets: Ices and organics on Sedna, Gonggong, and Quaoar from JWST spectroscopy |url=https://www.sciencedirect.com/science/article/pii/S0019103524000769 |journal=Icarus |volume=414 |pages=116017 |doi=10.1016/j.icarus.2024.116017 |bibcode=2024Icar..41416017E |issn=0019-1035 |quote=Spectra of all three objects show steep red spectral slopes and strong, broad absorptions between 2.7 and 3.6 μm indicative of complex organic molecules......These differences of Sedna, Gonggong, and Quaoar from the smaller KBO population supports the inference of different evolutionary history based on their size.|arxiv=2309.15230 }}</ref> Sedna has no detectable atmosphere, as its temperature is far too low for solids to [[Sublimation (phase transition)|volatilize]].<ref>{{Cite journal |last1=Emery |first1=J. P. |last2=Wong |first2=I. |last3=Brunetto |first3=R. |last4=Cook |first4=J. C. |last5=Pinilla-Alonso |first5=N. |last6=Stansberry |first6=J. A. |last7=Holler |first7=B. J. |last8=Grundy |first8=W. M. |last9=Protopapa |first9=S. |last10=Souza-Feliciano |first10=A. C. |last11=Fernández-Valenzuela |first11=E. |last12=Lunine |first12=J. I. |last13=Hines |first13=D. C. |date=2024-05-15 |title=A tale of 3 dwarf planets: Ices and organics on Sedna, Gonggong, and Quaoar from JWST spectroscopy |url=https://www.sciencedirect.com/science/article/pii/S0019103524000769 |journal=Icarus |volume=414 |doi=10.1016/j.icarus.2024.116017 |bibcode=2024Icar..41416017E |issn=0019-1035 |quote=...Sedna is not expected to support an atmosphere at its great distances... |via=Elsevier Science Direct|arxiv=2309.15230 }}</ref> Within range of uncertainty, it is tied with the dwarf planet {{dp|Ceres}} in the [[asteroid belt]] as the [[List of Solar System objects by size|largest dwarf planet]] not known to have a [[Natural satellite|moon]]. With a diameter of roughly 1,000&nbsp;km,<ref>{{Cite journal |last1=Bettati |first1=Amelia |last2=Lunine |first2=Jonathan |date=2025-04-01 |title=Atmospheric escape explains diverse surface compositions of Pluto vs Sedna |journal=Icarus |volume=430 |page=1 |doi=10.1016/j.icarus.2025.116482 |issn=0019-1035 |quote=...Although the radius is also uncertain, we minimize the number of cases by taking an average radius of 1000 km for Sedna... |doi-access=free |bibcode=2025Icar..43016482B }}</ref> it is nearly the size of [[Tethys (moon)|Tethys]] around [[Saturn]]. Owing to its lack of known moons,<ref>{{Cite journal |last1=Bettati |first1=Amelia |last2=Lunine |first2=Jonathan |date=2025-04-01 |title=Atmospheric escape explains diverse surface compositions of Pluto vs Sedna |journal=Icarus |volume=430 |page=12 |doi=10.1016/j.icarus.2025.116482 |issn=0019-1035 |quote=...No moon has been detected around Sedna, so it is not yet possible to calculate its density,... |doi-access=free |bibcode=2025Icar..43016482B }}</ref> the [[Kepler's laws of planetary motion|Keplerian laws]] of planetary motion cannot be utilized for determining its mass, and the actual figure remains as yet unknown.

Sedna's orbit is [[List of Solar System objects most distant from the Sun|one of the widest known]] in the Solar System. Its [[apsis|aphelion]], the farthest point from the Sun in its orbit, is located 937&nbsp;[[astronomical unit]]s (AU) away.<ref name="barycenter"/> This is some 19 times that of [[Pluto]], leading to its spending most of its time well beyond the [[Heliopause (astronomy)|heliopause]] (120 AU),<ref>{{Cite journal |last1=Emery |first1=J. P. |last2=Wong |first2=I. |last3=Brunetto |first3=R. |last4=Cook |first4=J. C. |last5=Pinilla-Alonso |first5=N. |last6=Stansberry |first6=J. A. |last7=Holler |first7=B. J. |last8=Grundy |first8=W. M. |last9=Protopapa |first9=S. |last10=Souza-Feliciano |first10=A. C. |last11=Fernández-Valenzuela |first11=E. |last12=Lunine |first12=J. I. |last13=Hines |first13=D. C. |date=2024-05-15 |title=A tale of 3 dwarf planets: Ices and organics on Sedna, Gonggong, and Quaoar from JWST spectroscopy |journal=Icarus |volume=414 |page=12, right paragraph 3 |doi=10.1016/j.icarus.2024.116017 |issn=0019-1035 |quote=...Sedna spends most of its time outside of the heliopause (at ~120 AU; e.g., Stone et al., 2013, 2019),... |doi-access=free|bibcode=2024Icar..41416017E |arxiv=2309.15230 }}</ref> the boundary beyond which the influences of particles from [[interstellar space]] dominate those from the Sun. Sedna's orbit is also one of the most elliptical and narrow discovered, with an [[Orbital eccentricity|eccentricity]] of 0.8496. This implies that its [[perihelion]], or point of closest approach to the Sun, at 76 AU is around 12.3 times as close as its aphelion. {{As of|2025|February}}, Sedna is {{convert|83.20|AU|e9km|abbr=unit|lk=out|sigfig=4}} from the Sun,<ref>{{Cite web |title=Asteroid 90377 Sedna (2003 VB12) {{!}} TheSkyLive |url=https://theskylive.com/sedna-info |access-date=2025-02-15 |website=theskylive.com}}</ref> approaching perihelion at ~4.4 km/s,<ref>Conservation of specific kinetic + potential energy, with Sun's gravitational parameter substituted.

<math>\frac{1.327 \cdot 10^{20}}{1.495 \cdot 10^{8}} \, \left(\frac{1}{83.2} - \frac{1}{937}\right) = \frac{1}{2} \, \left(x^{2} - 377^{2}\right)</math></ref> and 2.5 times as far away as [[Neptune]]. The dwarf planets {{dp|Eris}} and {{dp|Gonggong}} are presently farther away from the Sun.  A [[Interplanetary spaceflight#Launch windows|transfer window]] for a probe [[Flyby (spaceflight)#Kuiper belt|fly-by]] in 2029 utilizing a [[Gravity assist|gravitational assist]] from [[Jupiter]] was proposed, taking 25 years to travel to the dwarf planet, 80 AU (12 billion kilometers) distant.<ref>{{Cite journal |last1=Zubko |first1=V. A. |last2=Sukhanov |first2=A. A. |last3=Fedyaev |first3=K. S. |last4=Koryanov |first4=V. V. |last5=Belyaev |first5=A. A. |date=2021-10-01 |title=Analysis of mission opportunities to Sedna in 2029–2034 |url=https://www.sciencedirect.com/science/article/abs/pii/S0273117721004555 |journal=Advances in Space Research |volume=68 |issue=7 |pages=2752–2775 |doi=10.1016/j.asr.2021.05.035 |arxiv=2112.13017 |bibcode=2021AdSpR..68.2752Z |issn=0273-1177 |quote=...Results of the research presented in this article show that the launch in 2029 provides the best transfer conditions in terms of minimum total characteristic velocity... |via=Elsevier Science Direct}}</ref>

Due to its exceptionally [[Flattening|elongated]] orbit, the dwarf planet takes approximately 11,400 years, or over 11 millennia, to return to the same point in its orbit around the Sun. The [[International Astronomical Union]] (IAU) initially considered Sedna to be a member of the [[scattered disc]], a group of objects sent into high-eccentricity orbits by the gravitational influence of Neptune. However, several astronomers who worked in the associated field contested this classification as even its perihelion is far too distant for it to have been scattered by any of the currently known planets. This has led some astronomers to informally refer to it as the first known member of the [[Hills cloud|inner Oort cloud]]. The dwarf planet is also the prototype of a new orbit class of objects named after itself, the [[sednoid]]s, which include {{mpl|2012 VP|113}} and [[541132 Leleākūhonua|Leleākūhonua]], both celestial bodies with large perihelion distances and high eccentricities.<ref>{{Cite journal |last1=Huang |first1=Yukun |last2=Gladman |first2=Brett |date=2024-02-15 |title=Primordial Orbital Alignment of Sednoids |journal=The Astrophysical Journal Letters |language=en |volume=962 |issue=2 |pages=L33 |doi=10.3847/2041-8213/ad2686 |doi-access=free |arxiv=2310.20614 |bibcode=2024ApJ...962L..33H |issn=2041-8205 |quote=We examined the past history of the three most detached trans-Neptunian objects (TNOs)—Sedna, 2012 VP113, and Leleakuhonua (2015 TG387)—the three clearest members of the dynamical class known as sednoids, with high perihelia distances q... }}</ref>

The astronomer [[Michael E. Brown]], co-discoverer of Sedna, believes that studying Sedna's unusual orbit could yield valuable information on the origin and early evolution of the Solar System.<ref name="fussman"/><ref name=Chang_2016/> It might have been [[Perturbation (astronomy)|perturbed]] into its orbit by a star  within the Sun's [[Open cluster|birth cluster]], or captured from a nearby wandering star, or to have been sent into its present orbit through a close gravitational encounter with the hypothetical [[Planet Nine|9th planet]], sometime during the solar system's formation.<ref>{{Cite journal |last1=Zubko |first1=V. A. |last2=Sukhanov |first2=A. A. |last3=Fedyaev |first3=K. S. |last4=Koryanov |first4=V. V. |last5=Belyaev |first5=A. A. |date=2021-10-01 |title=Analysis of mission opportunities to Sedna in 2029–2034 |url=https://www.sciencedirect.com/science/article/abs/pii/S0273117721004555 |journal=Advances in Space Research |volume=68 |issue=7 |pages=2752–2775 |doi=10.1016/j.asr.2021.05.035 |arxiv=2112.13017 |bibcode=2021AdSpR..68.2752Z |issn=0273-1177 |quote=The discoverers (Brown et al., 2004) have supposed that Sedna was created in the Solar System at the early stage of its evolution, and its orbit was changed because of dynamic effects that followed the Sun’s formation within a dense stellar cluster (Brown et al., 2004, Morbidelli and Levison, 2004, Kenyon and Bromley, 2004, Adams, 2010, Kaib et al., 2011, Brasser and Schwamb, 2015). According to other versions, Sedna’s orbit was changed by a stellar encounter (Kaib and Quinn, 2008) (e.g., the passing Scholz’s star about 70 thousand years ago (Mamajek et al., 2015) at a distance of 52 thousand au from the Sun), or Sedna was captured from a low-mass star or a brown dwarf in interstellar space (Morbidelli and Levison, 2004). |via=Elsevier Science Direct}}</ref> The statistically unusual clustering to one side of the solar system of the aphelions of Sedna and other similar objects is speculated to be the evidence for the existence of a [[planets beyond Neptune|planet beyond the orbit of Neptune]],<ref>{{Cite journal |last1=Batygin |first1=Konstantin |last2=Brown |first2=Michael E. |title=Evidence for a Distant Giant Planet in the Solar System |journal=[[The Astronomical Journal]] |language=en |publication-place=Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125. |publication-date=2016-01-20 |volume=151 |issue=2 |page=22 |doi=10.3847/0004-6256/151/2/22 |quote=ABSTRACT Recent analyses have shown that distant orbits within the scattered disk population of the Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion....In this work we show that the orbits of distant Kuiper Belt objects (KBOs) cluster not only in argument of perihelion, but also in physical space. We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance....can be maintained by a distant eccentric planet with mass 10 m⊕ .... whose perihelion is 180° away from the perihelia of the minor bodies....Continued analysis ....provides the opportunity for testing our hypothesis as well as further constraining the orbital elements and mass of the distant planet. |postscript=This is THE paper. The paper that started everything, that which set things in motions unpredictable. |doi-access=free|bibcode=2016AJ....151...22B |arxiv=1601.05438 }}</ref> which would by itself orbit on the opposing side of the Sun.<ref name="Mike"/><ref name=Lakdawalla_2014/><ref name="Evidence for a Distant Giant Planet"/>

== History ==

=== Discovery ===
Sedna ([[provisional designation|provisionally designated]] '''{{mp|2003 VB|12}}''') was discovered by Michael Brown ([[California Institute of Technology|Caltech]]), [[Chad Trujillo]] ([[Gemini Observatory]]), and [[David Rabinowitz]] ([[Yale University]]) on 14 November 2003. The discovery formed part of a survey begun in 2001 with the [[Samuel Oschin telescope]] at [[Palomar Observatory]] near [[San Diego, California|San Diego]], [[California]], using Yale's 160-megapixel [[Palomar Observatory#QUEST|Palomar Quest camera]]. On that day, an object was observed to move by 4.6 [[Minute of arc|arcseconds]] over 3.1 hours relative to stars, which indicated that its distance was about 100&nbsp;AU. Follow-up observations were made in November–December 2003 with the SMARTS (Small and Medium Research Telescope System) at [[Cerro Tololo Inter-American Observatory]] in [[Chile]], the Tenagra IV telescope in [[Nogales, Arizona]], and the [[Keck Observatory]] on [[Mauna Kea]] in Hawaii. Combined with [[precovery]] observations taken at the Samuel Oschin telescope in August 2003, and by the [[Near-Earth Asteroid Tracking]] consortium in 2001–2002, these observations allowed the accurate determination of its orbit. The calculations showed that the object was moving along a distant and highly [[orbital eccentricity|eccentric]] orbit, at a distance of 90.3 AU from the Sun.<ref name="2004-E45"/><ref name="Mike"/> Precovery images have since been found in the [[Digitized Sky Survey|Palomar Digitized Sky Survey]] dating back to 25 September 1990.<ref name="jpldata" />

=== Naming ===
Brown initially nicknamed Sedna "[[The Flying Dutchman]]", or "Dutch", after a legendary [[ghost ship]], because its slow movement had initially masked its presence from his team.<ref name="plutokiller">{{cite book |title=How I Killed Pluto And Why It Had It Coming |first=Michael E. | last=Brown |publisher=Spiegel & Grau |year=2012 |location=New York |isbn=978-0-385-53110-8 |page=96 |author-link=Michael E. Brown}}</ref> He eventually settled on the official name after the goddess [[Sedna (mythology)|Sedna]] from [[Inuit mythology]], partly because he mistakenly thought the Inuit were the closest polar culture to his home in [[Pasadena, California|Pasadena]], and partly because the name, unlike [[Quaoar]], would be easily pronounceable by English speakers.<ref name="plutokiller"/> Brown further justified his choice of naming by stating that the goddess Sedna's traditional location at the bottom of the [[Arctic Ocean]] reflected Sedna's large distance from the Sun.<ref name="mikebrown"/> He suggested to the [[International Astronomical Union]]'s (IAU) [[Minor Planet Center]] that any objects discovered in Sedna's orbital region in the future should be named after mythical entities in Arctic mythologies.<ref name="mikebrown" />

The team made the name "Sedna" public before the object had been officially numbered, which caused some controversy among the community of amateur astronomers.<ref name="mpc">{{cite web|title=MPEC 2004-S73: Editorial Notice|publisher=IAU Minor Planet Center|url=https://minorplanetcenter.net/mpec/K04/K04S73.html|year=2004|accessdate=18 July 2010|archive-date=8 May 2020|archive-url=https://web.archive.org/web/20200508090811/https://minorplanetcenter.net//mpec/K04/K04S73.html|url-status=live}}</ref> [[Brian G. Marsden|Brian Marsden]], the head of the Minor Planet Center, stated that such an action was a violation of protocol, and that some members of the IAU might vote against it.<ref name="Walker"/> One amateur astronomer, [[Reiner Stoss]], unsuccessfully attempted to name one of his asteroid discoveries "Sedna" (after the singer Katy Sedna) in protest of Brown's premature naming.<ref name="mpc"/><ref name="nyt">{{cite news|title=10 Planets? Why Not 11?|url=https://www.nytimes.com/2005/08/23/science/space/10-planets-why-not-11.html|first=Kenneth|last=Chang|work=The New York Times|date=23 August 2005|accessdate=17 February 2025}}</ref><ref name="planetx">{{cite book|title=The Hunt for Planet X: New Worlds and the Fate of Pluto|url=https://link.springer.com/content/pdf/10.1007/978-0-387-77805-1.pdf#page=210|first=Govert|last=Schilling|publisher=Springer|year=2009|accessdate=16 February 2025|isbn=978-0-387-77805-1|page=212| doi=10.1007/978-0-387-77805-1 }}</ref> Despite the complaints by amateur astronomers, no objection was raised to Brown's name by members of the IAU and no competing names were suggested for Brown's object.<ref name="mpc"/> The IAU's [[Committee on Small Body Nomenclature]] accepted the name in September 2004,<ref name="MPC_20040928"/> and considered that, in similar cases of extraordinary interest, it might in the future allow names to be announced before they were officially numbered.<ref name="mpc"/>

Sedna has no symbol in astronomical literature, as the usage of [[planetary symbol]]s is discouraged in astronomy. [[Unicode]] includes a symbol {{angbr|[[File:Sedna symbol (fixed width).svg|16px|⯲]]}} (U+2BF2),<ref>{{cite web |url=https://www.unicode.org/charts/PDF/U2B00.pdf |title=Miscellaneous Symbols and Arrows |author=<!--Not stated--> |date=1991–2021 |website=unicode.org |publisher=Unicode |access-date=6 August 2022 |quote=2BF2 ⯲ SEDNA |archive-date=2 August 2022 |archive-url=https://web.archive.org/web/20220802202914/https://www.unicode.org/charts/PDF/U2B00.pdf |url-status=live }}</ref> but this is mostly used among [[astrologers]].<ref name=faulks>{{cite web|url=https://www.unicode.org/L2/L2016/16173-eris-sedna.pdf|title=Eris and Sedna Symbols|last=Faulks|first=David|date=12 June 2016|website=unicode.org|archive-url=https://archive.today/20170508160706/http://www.unicode.org/L2/L2016/16173-eris-sedna.pdf|archive-date=8 May 2017|url-status=dead}}</ref> The symbol is a monogram of {{langx|iu|ᓴᓐᓇ}} ''Sanna'', the modern pronunciation of Sedna's name.<ref name=faulks/>

== Orbit and rotation ==
{{See also|List of Solar System objects most distant from the Sun}}
{{multiple image
| direction         = vertical
| image1            = Sedna solar system Jan1 2017.png
| caption1          = The orbit of Sedna set against the orbits of outer Solar System objects (top and side views, Pluto's orbit is purple, Neptune's is blue)
| alt1              = A large oval represents the orbit of Sedna around the offset Sun and smaller, more circular planetary orbits
| image2            = Sednoid apparent magnitudes.png
| caption2          = The 10,000 year [[apparent magnitude]]s of Sedna and two other sednoids
| alt2              = A grid chart showing smoothly varying brightness over time
}}

Sedna has the longest [[orbital period]] of any known object in the Solar System of its size or larger with an orbital period of around 11,400 years.<ref name="barycenter"/>{{refn|1=Given the [[orbital eccentricity]] of this object, different [[Epoch (astronomy)|epochs]] can generate quite different heliocentric unperturbed [[Two-body problem|two-body]] [[curve fitting|best-fit]] solutions to the orbital period. Using a 1990 epoch, Sedna has a 12,100-year orbit,<ref name="DES" /> but using a 2019 epoch Sedna has a 10,500-year orbit.<ref>{{cite web | url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna | publisher=JPL | title=SBDB Epoch 2019 | archive-url=https://web.archive.org/web/20191113081024/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna | archive-date=13 November 2019 }}</ref> For objects at such high eccentricity, the Solar System's [[barycenter]] (Sun+Jupiter) generates solutions that are more stable than heliocentric solutions.<ref name="Kaib2009" /> Using [[JPL Horizons On-Line Ephemeris System|JPL Horizons]], the barycentric orbital period is consistently about 11,388&nbsp;years, with a variation of 2 years over the next two centuries.<ref name="barycenter" />|name=footnoteG|group=lower-alpha}} Its [[orbit]] is extremely eccentric, with an [[aphelion]] of approximately 937 AU<ref name="barycenter"/> and a [[Perihelion and aphelion|perihelion]] of 76.19 AU. Near aphelion, Sedna is one of the coldest places in the [[Solar System]], located far past the [[Heliosphere|termination shock]], where temperatures never exceed −240°[[Celsius|C]] (−400°[[Fahrenheit|F]]) due to its extreme distance.<ref>{{Cite web |title=Mysterious Sedna {{!}} Science Mission Directorate |url=https://science.nasa.gov/science-news/science-at-nasa/2004/16mar_sedna/ |access-date=31 March 2023 |website=science.nasa.gov |archive-date=16 May 2017 |archive-url=https://web.archive.org/web/20170516234331/https://science.nasa.gov/science-news/science-at-nasa/2004/16mar_sedna |url-status=dead }}</ref><ref>{{Cite web | title=Most Distant Object in Solar System Discovered | date=15 March 2004 | url=https://www.jpl.nasa.gov/news/most-distant-object-in-solar-system-discovered | access-date=31 March 2023 | website=NASA Jet Propulsion Laboratory (JPL) | language=en-US | archive-date=22 October 2023 | archive-url=https://web.archive.org/web/20231022073655/https://www.jpl.nasa.gov/news/most-distant-object-in-solar-system-discovered | url-status=live }}</ref> At aphelion, Sun as viewed from Sedna is a particularly bright star, among the other stars, in the otherwise black sky, being about 45% as bright as the full moon as seen from Earth.<ref>Apparent magnitude of Sun at 937 AU = -26.74 + 5log(937) = -11.88

Full moon magnitude = -12.74

Ratio = 10^(0.4*(11.88-12.74)) = 0.453 ≈ 45%.</ref> Its perihelion was the largest for any known Solar System object until the discovery of the [[sednoid]] {{mpl|2012 VP|113}}.<ref name="Trujillo2007"/><ref name="Trujillo2014"/> At its aphelion, Sedna orbits the Sun at a meagre 377&nbsp;m/s,<ref>Calculated: https://www.wolframalpha.com/input?i=G*solar+mass%2FAU%281%2F76.19-1%2F937%29%3D1%2F2*%28x+m%2Fs%29%5E2%28%28937%2F76.19%29%5E2-1%29</ref> 1.3% that of Earth's average orbital speed.<ref>377.4 m/s for Sedna divided by 29.78 km/s for Earth.</ref>

When Sedna was first discovered, it was 89.6&nbsp;AU<ref name="AstDys2003"/> away from the Sun, approaching perihelion, and was the most distant object in the Solar System observed. Sedna was later surpassed by [[Eris (dwarf planet)|Eris]], which was detected by the same survey near its aphelion at 97&nbsp;AU. Because Sedna is near perihelion {{as of|2024|lc=y}}, both Eris and {{dp|Gonggong}} are farther from the Sun, at 96&nbsp;AU and 89&nbsp;AU respectively, than Sedna at 84&nbsp;AU, despite both of their semi-major axes being shorter than Sedna's.<ref name="AstDys-Eris" /><ref name="AstDys-OR10" /><ref name="AstDys" /> The orbits of some long-period comets extend further than that of Sedna; they are too dim to be discovered except when approaching perihelion in the inner Solar System. As Sedna nears its perihelion in mid-2076,<ref name="Perihelion2076"/>{{refn|1=Different programs using different [[Epoch (astronomy)|epochs]] and/or [[data set]]s will produce slightly different dates for Sedna's [[apsis|perihelion]] as they generate instantaneous unperturbed 2-body solutions. Using a 2020 epoch, the [[JPL Small-Body Database]] has a perihelion date of 9{{nbsp}}March 2076.<ref name="jpldata"/> Using a 1990 epoch the Lowell [[Deep Ecliptic Survey|DES]] has perihelion on [http://www.boulder.swri.edu/~buie/kbo/astrom/90377.html 2479285.9863] ([http://ssd.jpl.nasa.gov/tc.cgi 14{{nbsp}}December 2075]). {{As of|2021}}, the [[JPL Horizons On-Line Ephemeris System|JPL Horizons]] (using much more accurate [[numerical integration]]) indicates a perihelion date of 18{{nbsp}}July 2076.<ref name="Perihelion2076" />|name=footnoteC|group=lower-alpha}} the Sun will appear merely as a very bright pinpoint in its sky, the G-type star too far away to be visible as a disc to the naked eye.<ref name="HubbleSite2004image"/>

When first discovered, Sedna was thought to have an unusually long rotational period (20 to 50 days).<ref name="HubbleSite2004"/> It was initially speculated that Sedna's rotation was slowed by the gravitational pull of a large binary companion, similar to [[Pluto]]'s moon [[Charon (moon)|Charon]].<ref name="mikebrown" /> However, a search for such a satellite by the [[Hubble Space Telescope]] in March 2004 found no such objects.<ref name="HubbleSite2004"/>{{refn|1=The HST search found no satellite candidates to a limit of about 500 times fainter than Sedna (Brown and Suer 2007).<ref name="largest" />|group=lower-alpha}} Subsequent measurements from the [[MMT Observatory|MMT]] telescope showed that Sedna in reality has a much shorter rotation period of about 10 hours, more typical for a body its size. It could rotate in about 18 hours instead, but this is thought to be unlikely.<ref name="Gaudi2005"/>

== Physical characteristics ==
Sedna has a [[V band]] [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] of about 1.8, and is estimated to have an [[albedo]] (reflectivity) of around 0.41, giving it a diameter of approximately 900&nbsp;km.<ref name=herschel/> At the time of discovery it was the brightest object found in the Solar System since Pluto in 1930. In 2004, the discoverers placed an upper limit of 1,800&nbsp;km on its diameter;<ref name="Grundy2005"/> after observations by the [[Spitzer Space Telescope]], this was revised downward by 2007 to less than 1,600&nbsp;km.<ref name="spitzer"/> In 2012, measurements from the [[Herschel Space Observatory]] suggested that Sedna's diameter was {{nowrap|995 ± 80 km}}, which would make it smaller than Pluto's moon Charon.<ref name=herschel>{{cite journal |last1=Pál |first1=A. |last2=Kiss |first2=C. |last3=Müller |first3=T. G. |last4=Santos-Sanz |first4=P. |last5=Vilenius |first5=E. |last6=Szalai |first6=N. |last7=Mommert |first7=M. |last8=Lellouch |first8=E. |last9=Rengel |first9=M. |last10=Hartogh |first10=P. |last11=Protopapa |first11=S. |last12=Stansberry |first12=J. |last13=Ortiz |first13=J.-L. |last14=Duffard |first14=R. |last15=Thirouin |first15=A. |last16=Henry |first16=F. |last17=Delsanti |first17=A. |title="TNOs are Cool": A survey of the trans-Neptunian region. VII. Size and surface characteristics of (90377) Sedna and {{mp|2010 EK|139}} |doi=10.1051/0004-6361/201218874 |journal=Astronomy & Astrophysics |volume=541 |pages=L6 |year=2012 |bibcode= 2012A&A...541L...6P |arxiv=1204.0899|s2cid=119117186 }}</ref> In 2013, the same team re-analyzed Sedna's thermal data with an improved thermophysical model and found a consistent value of {{val|906|314|258|u=km}}, suggesting that the original model fit was too precise.<ref name="Lellouch A60">{{Cite journal |last1=Lellouch |first1=E. |last2=Santos-Sanz |first2=P. |last3=Lacerda |first3=P. |last4=Mommert |first4=M. |last5=Duffard |first5=R. |last6=Ortiz |first6=J. L. |last7=Müller |first7=T. G. |last8=Fornasier |first8=S. |last9=Stansberry |first9=J. |last10=Kiss |first10=Cs. |last11=Vilenius |first11=E. |last12=Mueller |first12=M. |last13=Peixinho |first13=N. |last14=Moreno |first14=R. |last15=Groussin |first15=O. |date=29 September 2013 |title="TNOs are Cool": A survey of the trans-Neptunian region: IX. Thermal properties of Kuiper belt objects and Centaurs from combined Herschel and Spitzer observations⋆⋆⋆ |journal=Astronomy & Astrophysics |volume=557 |pages=A60 |doi=10.1051/0004-6361/201322047 |issn=0004-6361|doi-access=free |bibcode=2013A&A...557A..60L |hdl=10316/80307 |hdl-access=free }}</ref> Australian observations of a [[stellar occultation]] by Sedna in 2013 produced similar results on its diameter, giving [[Chord (astronomy)|chord]] lengths {{val|1025|135|u=km}} and {{val|1305|565|u=km}}.<ref name="Rommel2020"/> The size of this object suggests it could have undergone [[Planetary differentiation|differentiation]] and may have a [[Planetary oceanography|sub-surface liquid ocean]] and possibly [[Planetary geology|geologic]] activity.<ref name="Emery2007"/>

As Sedna has no known moons, the direct determination of its mass is as yet impossible without either sending a [[space probe]] or perhaps locating a nearby object which is gravitationally [[Perturbation (astronomy)|perturbed]] by the planetoid. It is the largest trans-Neptunian Sun-orbiting object not known to have a natural satellite.<ref name = "Lakdawalla2016a" /> As of 2024, observations from the [[Hubble Space Telescope]] in 2004 have been the only published attempt to find a satellite,<ref name="HubbleProposal" /><ref name="Mystery" /> and it is possible that a satellite could have been lost in the glare from Sedna itself.<ref name="BannisterTwitter" />

Observations from the SMARTS telescope show that Sedna, in [[visible light]], is one of the reddest objects known in the Solar System, nearly as red as [[Mars]].<ref name="mikebrown"/> Its deep red [[spectral slope]] is indicative of high concentrations of [[organic chemistry|organic material]] on its surface.<ref name="Emery2007" /> Chad Trujillo and his colleagues suggest that Sedna's dark red color is caused by an extensive surface coating of [[hydrocarbon]] sludge, termed [[tholins]]. Tholins are a reddish-colored, amorphous, and heterogeneous organic mixture hypothesized to have been transmuted from simpler organic compounds, following billions of years of continuous exposure to [[ultraviolet]] radiation, interstellar particles, and other harsh environs as the dwarf planet either comes close to the Sun or transits interstellar space.<ref name="Trujillo2005"/> Its surface is homogeneous in color and [[spectrograph|spectrum]]; this may be because Sedna, unlike objects nearer the Sun, is rarely impacted by other bodies, which would expose bright patches of fresh icy material like that on [[8405 Asbolus]].<ref name="Trujillo2005"/> Sedna and two other very distant objects – {{mpl|2006 SQ|372}} and {{mpl|(87269) 2000 OO|67}} – share their color with outer [[classical Kuiper belt object]]s and the [[Centaur (planetoid)|centaur]] [[5145 Pholus]], suggesting a similar region of origin.<ref name="Sheppard2010"/>

Trujillo and colleagues have placed upper limits on Sedna's surface composition of 60% for methane ice and 70% for water ice.<ref name="Trujillo2005"/> The presence of methane further supports the existence of tholins on Sedna's surface, as methane is among the organic compounds capable of giving rise to tholins.<ref name="Emery2007"/> Barucci and colleagues compared Sedna's spectrum with that of [[Triton (moon)|Triton]] and detected weak [[absorption bands]] belonging to methane and nitrogen ices. From these observations, they suggested the following model of the surface: 24% Triton-type tholins, 7% [[amorphous carbon]], 10% nitrogen ices, 26% [[methanol]], and 33% methane.<ref name="Triton"/> The detection of methane and water ice was confirmed in 2006 by the Spitzer Space Telescope [[mid-infrared]] photometry.<ref name="Emery2007"/> The [[European Southern Observatory]]'s [[Very Large Telescope]] observed Sedna with the SINFONI [[near-infrared]] spectrometer, finding indications of tholins and water ice on the surface.<ref name="Barucci_et_al_2010">{{cite journal |last1=Barucci |first1=M. A. |last2=Morea Dalle Ore |first2=C.|author2-link=Cristina Dalle Ore |last3=Alvarez-Candal |first3=A. |last4=de Bergh |first4=C. |last5=Merlin |first5=F. |last6=Dumas |first6=C. |last7=Cruikshank |first7=D. |title=(90377) Sedna: Investigation of Surface Compositional Variation |journal=[[The Astronomical Journal]] |volume=140 |issue=6 |pages=2095–2100 |date=December 2010 |doi=10.1088/0004-6256/140/6/2095 |bibcode=2010AJ....140.2095B |s2cid=120483473 |doi-access=free }}</ref>

In 2022, low-resolution near-infrared (0.7–5 μm) [[spectroscopy|spectroscopic]] observations by the [[James Webb Space Telescope]] (JWST) revealed the presence of significant amounts of [[ethane]] ice (C<sub>2</sub>H<sub>6</sub>) and of complex organics on the surface of Sedna. The JWST spectra also contain evidence of the existence of small amounts of [[ethylene]] (C<sub>2</sub>H<sub>4</sub>), [[acetylene]] (C<sub>2</sub>H<sub>2</sub>) and possibly [[carbon dioxide]] (CO<sub>2</sub>). On the other hand little evidence of the existence of [[methane]] (CH<sub>4</sub>) and nitrogen ices was found at variance with the earlier observations.<ref name="Emery2024"/>

The possible presence of nitrogen on the surface suggests that, at least for a short time, Sedna may have a tenuous atmosphere. During the 200-year portion of its orbit near perihelion, the maximum temperature on Sedna should exceed {{convert|35.6|K|C}}, the transition temperature between alpha-phase solid N<sub>2</sub> and the beta-phase seen on Triton. At 38&nbsp;K, the N<sub>2</sub> [[vapor pressure]] would be 14&nbsp;microbar (1.4&nbsp;Pa). The weak methane absorption bands indicate that methane on Sedna's surface is ancient, as opposed to being freshly deposited. This finding indicates that Sedna's surface never reaches a temperature high enough for methane on the surface to evaporate and subsequently fall back as snow, which happens on Triton and probably on Pluto.<ref name="Emery2007"/>

== Origin ==
In their paper announcing the discovery of Sedna, Brown and his colleagues described it as the first observed body belonging to the [[Oort cloud]], the hypothetical cloud of [[comet]]-like objects thought to exist out to nearly a light-year from the Sun. They observed that, unlike [[scattered disc]] objects such as Eris, Sedna's perihelion (76&nbsp;AU) is too distant for it to have been scattered by the gravitational influence of Neptune.<ref name="Mike"/> Because it is considerably closer to the Sun than was expected for an Oort cloud object, and has an [[inclination]] roughly in line with the planets and the Kuiper belt, they described the planetoid as being an "inner Oort cloud object", situated in the disc reaching from the Kuiper belt to the spherical part of the cloud.<ref name="Swiss" /><ref name="LykDyn"/>

If Sedna formed in its current location, the Sun's original [[protoplanetary disc]] must have extended as far as 75&nbsp;AU into space.<ref name="SternAJ2005"/> On top of that, Sedna's initial orbit must have been approximately circular, otherwise its formation by the [[accretion (astrophysics)|accretion]] of smaller bodies into a whole would not have been possible, because the large [[relative velocity|relative velocities]] between planetesimals would have been too disruptive. Therefore, it must have been tugged into its current eccentric orbit by a gravitational interaction with another body.<ref name="scattered"/> In their initial paper, Brown, Rabinowitz and colleagues suggested three possible candidates for the perturbing body: an unseen planet beyond the Kuiper belt, a single [[List of nearest stars#Future and past|passing star]], or one of the young stars embedded with the Sun in the stellar cluster in which it formed.<ref name="Mike"/>

Brown and his team favored the hypothesis that Sedna was lifted into its current orbit by a star from the Sun's [[birth cluster]], arguing that Sedna's aphelion of about 1,000&nbsp;AU, which is relatively close compared to those of long-period comets, is not distant enough to be affected by passing stars at their current distances from the Sun. They propose that Sedna's orbit is best explained by the Sun having formed in an [[open cluster]] of several stars that gradually disassociated over time.<ref name="Mike"/><ref name="Brown2004AAS205"/><ref name="PlanetarySociety"/> That hypothesis has also been advanced by both [[Alessandro Morbidelli (astronomer)|Alessandro Morbidelli]] and [[Scott Jay Kenyon]].<ref name="Morbidelli2004"/><ref name="Kenyon2004"/> Computer simulations by [[Julio A. Fernandez]] and Adrian Brunini suggest that multiple close passes by young stars in such a cluster would pull many objects into Sedna-like orbits.<ref name="Mike"/> A study by Morbidelli and [[Harold F. Levison|Levison]] suggested that the most likely explanation for Sedna's orbit was that it had been perturbed by a close (approximately 800&nbsp;AU) pass by another star in the first 100 million years or so of the Solar System's existence.<ref name="Morbidelli2004"/><ref name="challenge"/>

{{TNO imagemap}}

The [[trans-Neptunian planet]] hypothesis has been advanced in several forms by numerous astronomers, including Rodney Gomes and Patryk Lykawka. One scenario involves perturbations of Sedna's orbit by a hypothetical planetary-sized body in the [[Hills cloud|inner Oort cloud]]. In 2006, simulations suggested that Sedna's orbital traits could be explained by perturbations of a Jupiter-mass ({{Jupiter mass|link=y}}) object at 5,000&nbsp;AU (or less), a Neptune-mass object at 2,000&nbsp;AU, or even an Earth-mass object at 1,000&nbsp;AU.<ref name="PlanetarySociety"/><ref name="Gomez2006"/> Computer simulations by Patryk Lykawka have indicated that Sedna's orbit may have been caused by a body roughly the size of Earth, ejected outward by Neptune early in the Solar System's formation and currently in an elongated orbit between 80 and 170&nbsp;AU from the Sun.<ref name="lykawka"/> Brown's various sky surveys have not detected any Earth-sized objects out to a distance of about 100&nbsp;AU. It's a possibility that such an object may have been scattered out of the Solar System after the formation of the inner Oort cloud.<ref name="sisters"/>

Caltech researchers [[Konstantin Batygin]] and Mike Brown have hypothesized the existence of a [[super-Earth]] planet in the outer Solar System—[[Planet Nine]]—to explain the orbits of a group of [[extreme trans-Neptunian object]]s that includes Sedna.<ref name="Evidence for a Distant Giant Planet"/><ref>{{cite press release |last=Fesenmaier |first=Kimm |title=Caltech Researchers Find Evidence of a Real Ninth Planet |date=20 January 2016 |url=http://www.caltech.edu/news/caltech-researchers-find-evidence-real-ninth-planet-49523 |access-date=13 September 2017 |archive-date=16 January 2019 |archive-url=https://web.archive.org/web/20190116051438/http://www.caltech.edu/news/caltech-researchers-find-evidence-real-ninth-planet-49523 |url-status=live }}</ref> This planet would be perhaps six times as massive as Earth.<ref name="Brown_Batygin_2021z">{{cite journal |last1=Brown |first1=Michael E. |last2=Batygin |first2=Konstantin |title=A search for Planet Nine using the Zwicky Transient Facility public archive |journal=The Astronomical Journal |date=31 January 2022 |volume=163 |issue=2 |page=102 |arxiv=2110.13117 |bibcode=2022AJ....163..102B |doi=10.3847/1538-3881/ac32dd |s2cid=239768690 |doi-access=free }}</ref> It would have a highly eccentric orbit, and its average distance from the Sun would be about 15 times that of Neptune (which orbits at an average distance of {{convert|30.1|AU|km}}). Accordingly, its orbital period would be approximately 7,000 to 15,000 years.<ref name="Brown_Batygin_2021z"/>

Morbidelli and Kenyon have suggested that Sedna did not originate in the Solar System, but was captured by the Sun from a passing extrasolar [[planetary system]], specifically that of a [[brown dwarf]] about 1/20th the mass of the Sun ({{Solar mass|link=y}})<ref name="Morbidelli2004" /><ref name="Kenyon2004" /><ref>{{cite journal |url=http://www.scientificamerican.com/article/sun-accused-of-stealing-planetary-objects-from-another-star/ |title=Sun Accused of Stealing Planetary Objects from Another Star |first=Ken |last=Croswell |journal=Scientific American |year=2015 |volume=313 |issue=3 |page=23 |doi=10.1038/scientificamerican0915-23 |pmid=26455093 |access-date=15 January 2023 |archive-date=8 June 2021 |archive-url=https://web.archive.org/web/20210608202044/https://www.scientificamerican.com/article/sun-accused-of-stealing-planetary-objects-from-another-star/ |url-status=live }}</ref> or a [[main-sequence]] star 80 percent more massive than the Sun, which, owing to its larger mass, may now be a [[white dwarf]]. In either case, the stellar encounter had likely occurred within 100 million years after the Sun's formation.<ref name="Morbidelli2004" /><ref>{{cite web | url=https://www.newscientist.com/article/dn27757-grand-theft-sedna-how-the-sun-might-have-stolen-a-mini-planet/ | title=Grand Theft Sedna: how the sun might have stolen a mini-planet | first=Govert | last=Schilling | date=19 June 2015 | work=New Scientist | access-date=15 January 2023 | archive-date=20 December 2021 | archive-url=https://web.archive.org/web/20211220224559/https://www.newscientist.com/article/dn27757-grand-theft-sedna-how-the-sun-might-have-stolen-a-mini-planet/ | url-status=live }}</ref><ref>{{Cite web | first=David | last=Dickinson | url=https://www.universetoday.com/121637/stealing-sedna/ | title=Stealing Sedna | website=universetoday | date=6 August 2015 | access-date=15 January 2023 | archive-date=15 November 2021 | archive-url=https://web.archive.org/web/20211115221456/https://www.universetoday.com/121637/stealing-sedna/ | url-status=live }}</ref> Stellar encounters during this time would have minimal effect on the Oort cloud's final mass and population since the Sun had excess material for replenishing the Oort cloud.<ref name="Morbidelli2004" />

== Population ==
{{Main|Sednoid}}
[[File:Sednoid orbits.png|thumb|Orbit diagram of Sedna, {{mpl|2012 VP|113}}, and [[541132 Leleākūhonua|Leleākūhonua]] with 100 AU grids for scale|alt=Three overlapping ovals represent the orbits]]

Sedna's highly elliptical orbit, and thus a narrow temporal window for detection and observation with currently available technology, means that the probability of its detection was roughly 1 in 80. [[Bayesian inference|Unless its discovery were a fluke]], it is expected that another 40–120 Sedna-sized objects with roughly the same orbital parameters would exist in the outer solar system.<ref name="Mike" /><ref name="largest" />

In 2007, astronomer [[Megan Schwamb]] outlined how each of the proposed mechanisms for Sedna's extreme orbit would affect the structure and dynamics of any wider population. If a trans-Neptunian planet was responsible, all such objects would share roughly the same perihelion (about 80&nbsp;AU). If Sedna was captured from another planetary system that rotated in the same direction as the Solar System, then all of its population would have orbits on relatively low inclinations and have [[Semi-major and semi-minor axes|semi-major axes]] ranging from 100 to 500&nbsp;AU. If it rotated in the opposite direction, then two populations would form, one with low and one with high inclinations. The perturbations from passing stars would produce a wide variety of perihelia and inclinations, each dependent on the number and angle of such encounters.<ref name="sisters"/>

A larger sample of objects with Sedna's extreme perihelion may help in determining which scenario is most likely.<ref name="Schwamb"/> "I call Sedna a fossil record of the earliest Solar System", said Brown in 2006. "Eventually, when other fossil records are found, Sedna will help tell us how the Sun formed and the number of stars that were close to the Sun when it formed."<ref name="fussman"/> A 2007–2008 survey by Brown, Rabinowitz, and Megan Schwamb attempted to locate another member of Sedna's hypothetical population. Although the survey was sensitive to movement out to 1,000&nbsp;AU and discovered the likely dwarf planet Gonggong, it detected no new sednoid.<ref name="Schwamb" /> Subsequent simulations incorporating the new data suggested about 40 Sedna-sized objects probably exist in this region, with the brightest being about Eris's magnitude (−1.0).<ref name="Schwamb"/>

In 2014, Chad Trujillo and [[Scott S. Sheppard|Scott Sheppard]] announced the discovery of {{mpl|2012 VP|113}},<ref name="Trujillo2014"/> an object half the size of Sedna, a 4,200-year orbit similar to Sedna's, and a perihelion within Sedna's range of roughly 80&nbsp;AU;<ref name="jpldata 2012 VP113"/> they speculated that this similarity of orbits may be due to the gravitational shepherding effect of a trans-Neptunian planet.<ref name="Physorg"/> Another high-perihelion trans-Neptunian object was announced by Sheppard and colleagues in 2018, provisionally designated {{mp|2015 TG|387}} and now named [[541132 Leleākūhonua|Leleākūhonua]].<ref name="Carnegie2018"/> With a perihelion of 65&nbsp;AU and an even more distant orbit with a period of 40,000 years, its [[Longitude of the periapsis|longitude of perihelion]] (the location where it makes its closest approach to the Sun) appears to be aligned with the directions of both Sedna and {{mp|2012 VP|113}}, strengthening the case for an apparent orbital clustering of trans-Neptunian objects suspected to be influenced by a hypothetical distant planet, dubbed Planet Nine. In a study detailing Sedna's population and Leleākūhonua's orbital dynamics, Sheppard concluded that the discovery implies a population of about 2 million inner Oort Cloud objects larger than 40&nbsp;km, with a total mass in the range of {{val|1|e=22|u=kg}} (several times the mass of the asteroid belt and 80% the mass of Pluto).<ref name="Sheppard-2019"/>

Sedna was recovered from [[Transiting Exoplanet Survey Satellite]] data in 2020, as part of preliminary work for an all-sky survey searching for Planet Nine and other as-yet-unknown trans-Neptunian objects.<ref name="Rice_Laughlin_TESS_2020">{{cite journal |last1=Rice |first1=Malena |last2=Laughlin |first2=Gregory |title=Exploring Trans-Neptunian Space with TESS: A Targeted Shift-stacking Search for Planet Nine and Distant TNOs in the Galactic Plane |journal=[[The Planetary Science Journal]] |volume=1 |issue=3 |pages=81 (18 pp.) |date=December 2020 |arxiv=2010.13791 |doi=10.3847/PSJ/abc42c |bibcode=2020PSJ.....1...81R |s2cid=225075671 |doi-access=free }}</ref>

== Classification ==
The discovery of Sedna renewed the old question of just which [[astronomical object]]s ought to be considered [[planet]]s, and which ones ought not to be. On 15 March 2004, articles on Sedna in the popular press reported misleadingly that a tenth planet had been discovered. This question was resolved for many astronomers by applying the International Astronomical Union's [[IAU definition of planet|definition of a planet]], adopted on 24 August 2006, which mandated that a planet must have [[cleared the neighborhood]] around its orbit. Sedna is not expected to have cleared its neighborhood; quantitatively speaking, its [[Stern–Levison parameter]] is estimated to be much less than 1.{{refn|1=The Stern–Levison parameter (''Λ'') as defined by [[Alan Stern]] and [[Harold F. Levison]] in 2002 determines if an object will eventually clear its orbital neighborhood of small bodies. It is defined as the object's fraction of solar mass (i.e. the object's mass divided by the Sun's mass) squared, divided by its semi-major axis to the 3/2 power, times a constant 1.7{{e|16}}.<ref name="stern" /><sup>(see equation 4)</sup> If an object's Λ is greater than 1, then that object will eventually clear its neighborhood, and it can be considered for planethood. Using the unlikely highest estimated mass for Sedna of 2{{e|21}} kg, Sedna's Λ is (2{{e|21}}/[[Sun|1.9891{{e|30}}]])<sup>2</sup> / 519<sup>3/2</sup> × 1.7{{e|16}} = 1.44{{e|-6}}. This is much less than 1, so Sedna is not a planet by this criterion.|group=lower-alpha}} The IAU also adopted ''dwarf planet'' as a term for the largest non-planets (despite the name) that, like planets, are in [[hydrostatic equilibrium]] and thus can display planet-like geological activity, yet have not cleared their orbital neighborhoods.<ref name=planetarysociety>{{cite journal
 | title=What Is A Planet?
 | first=Emily
 | last=Lakdawalla
 | display-authors=et al
 | journal=The Planetary Society
 | date=21 April 2020
| url=https://www.planetary.org/worlds/what-is-a-planet
 | access-date=15 January 2023
| archive-date=22 January 2022
| archive-url=https://web.archive.org/web/20220122142140/https://www.planetary.org/worlds/what-is-a-planet
 | url-status=live
 }}</ref> Sedna is bright enough, and therefore large enough, that it is expected to be in hydrostatic equilibrium.<ref>{{Cite journal |last1=Rambaux |first1=Nicolas |last2=Baguet |first2=Daniel |last3=Chambat |first3=Frederic |last4=Castillo-Rogez |first4=Julie C. |date=15 November 2017 |title=Equilibrium Shapes of Large Trans-Neptunian Objects |journal=The Astrophysical Journal |volume=850 |issue=1 |pages=L9 |bibcode=2017ApJ...850L...9R |doi=10.3847/2041-8213/aa95bd |s2cid=62822239 |issn=2041-8213 |doi-access=free }}</ref> Hence, astronomers generally consider Sedna a dwarf planet.<ref name="Barucci_et_al_2010"/><ref>{{cite journal
 | title=SMARTS Studies of the Composition and Structure of Dwarf Planets
 | last1=Rabinowitz | first1=David L. | last2=Schaefer | first2=B.
 | last3=Tourtellotte | first3=S. | last4=Schaefer | first4=M.
 | journal=Bulletin of the American Astronomical Society
 | volume=43 | date=May 2011 | bibcode=2011AAS...21820401R
}}</ref><ref>{{cite journal
 | title=On the Importance of a Few Dwarf Planets
 | last=Malhotra | first=Renu
 | journal=Bulletin of the American Astronomical Society
 | volume=41 | page=740 | date=May 2009
 | bibcode=2009AAS...21423704M
}}</ref><ref name="Tancredi2008"/><ref name="Brown-dplist" /><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. |title=The mutual orbit, mass, and density of transneptunian binary Gǃkúnǁʼhòmdímà ({{mp|(229762) 2007 UK|126}}) |journal=Icarus |date=December 2019 |volume=334 |pages=30–38 |doi=10.1016/j.icarus.2018.12.037 |bibcode=2019Icar..334...30G |s2cid=126574999 |url=http://www2.lowell.edu/users/grundy/abstracts/preprints/2019.G-G.pdf |url-status=live |archive-url=https://web.archive.org/web/20190407045339/http://www2.lowell.edu/~grundy/abstracts/preprints/2019.G-G.pdf |archive-date=7 April 2019 }}</ref>

Besides its physical classification, Sedna is also categorized according to its orbit. The Minor Planet Center, which officially catalogs the objects in the Solar System, designates Sedna only as a trans-Neptunian object (as it orbits beyond Neptune),<ref>{{Cite web |date=21 June 2022 |title=List Of Transneptunian Objects |url=https://minorplanetcenter.net/iau/lists/TNOs.html |access-date=28 June 2022 |website=Minor Planet Center |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612142051/https://www.minorplanetcenter.net/iau/lists/TNOs.html |url-status=live }}</ref> as does the [[JPL Small-Body Database]].<ref>{{Cite web |title=Small-Body Database Lookup |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=90377 |access-date=28 June 2022 |website=ssd.jpl.nasa.gov |archive-date=6 October 2021 |archive-url=https://web.archive.org/web/20211006162446/https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=90377 |url-status=live }}</ref> The question of a more precise orbital classification has been much debated, and many astronomers have suggested that the [[sednoid]]s, together with similar objects such as {{mpl|2000 CR|105}}, be placed in a new category of distant objects named ''extended scattered disc objects'' (E-SDO),<ref name="Gladman" /> ''[[detached object]]s'',<ref name="Jewitt2006"/> ''distant detached objects'' (DDO),<ref name="Gomez2006" /> or ''scattered-extended'' in the formal classification by the [[Deep Ecliptic Survey]].<ref name="DES_Elliot2006"/>

== Exploration ==
Sedna will come to perihelion around July 2076.<ref name="Perihelion2076"/><ref group=lower-alpha name=footnoteC/> This close approach to the Sun provides a window of opportunity for studying it that will not occur again for more than 11 thousand years. Because Sedna spends much of its orbit beyond the [[Heliopause (astronomy)|heliopause]], the point at which the [[solar wind]] gives way to the [[Interstellar medium|interstellar particle wind]], examining Sedna's surface would provide unique information on the effects of interstellar radiation, as well as the properties of the solar wind at its farthest extent.<ref>{{cite journal
 | title=The fastest routes of approach to dwarf planet Sedna for studying its surface and composition at the close range
 | first=Vladislav | last=Zubko
 | journal=Acta Astronautica
 | volume=192 | date=March 2022 | pages=47–67
 | arxiv=2112.11506 | bibcode=2022AcAau.192...47Z
 | doi=10.1016/j.actaastro.2021.12.011 | s2cid=245172065 }}</ref> It was calculated in 2011 that a flyby mission to Sedna could take 24.48 years using a Jupiter [[gravity assist]], based on launch dates of 6 May 2033 or 23 June 2046. Sedna would be either 77.27 or 76.43&nbsp;AU from the Sun when the spacecraft arrives near the end of 2057 or 2070, respectively.<ref name=McGranaghan/> Other potential flight trajectories involve gravity assists from Venus, Earth, Saturn, and Neptune as well as Jupiter.<ref>{{Cite journal |last1=Zubko |first1=V. A. |last2=Sukhanov |first2=A. A. |last3=Fedyaev |first3=K. S. |last4=Koryanov |first4=V. V. |last5=Belyaev |first5=A. A. |date=October 2021 |title=Analysis of mission opportunities to Sedna in 2029–2034 |url=https://linkinghub.elsevier.com/retrieve/pii/S0273117721004555 |journal=Advances in Space Research |language=en |volume=68 |issue=7 |pages=2752–2775 |doi=10.1016/j.asr.2021.05.035 |arxiv=2112.13017 |bibcode=2021AdSpR..68.2752Z |s2cid=236278655 |access-date=11 July 2022 |archive-date=2 April 2022 |archive-url=https://web.archive.org/web/20220402034542/https://linkinghub.elsevier.com/retrieve/pii/S0273117721004555 |url-status=live }}</ref> Research at the University of Tennessee has also examined the potential for a lander.<ref>{{cite journal | title=Investigation of Interplanetary Trajectories to Sedna | first1=Samuel | last1=Brickley | first2=Iliane | last2=Domenech | first3=Lorenzo | last3=Franceschetti | first4=John | last4=Sarappo | first5=James Evans | last5=Lyne | journal=AAS 23-420, AAS/AIAA Astrodynamics Specialist Conference, Big Sky, Montana, August 2023 | date=May 2023 | url=https://trace.tennessee.edu/utk_chanhonoproj/2535/ | access-date=1 September 2023 | archive-date=2 September 2023 | archive-url=https://web.archive.org/web/20230902025743/https://trace.tennessee.edu/utk_chanhonoproj/2535/ | url-status=live }}</ref>

== Notes ==
{{reflist|2|group=lower-alpha}}

== References ==
{{reflist
| colwidth = 30em
| refs =

<ref name="2004-E45">{{cite web
| title = MPEC 2004-E45 : 2003 VB12
| publisher = IAU: Minor Planet Center
| url = https://minorplanetcenter.net/mpec/K04/K04E45.html
| date = 15 March 2004
| access-date = 27 March 2018
| archive-date = 28 October 2021
| archive-url = https://web.archive.org/web/20211028100038/https://minorplanetcenter.net/mpec/K04/K04E45.html
| url-status = live
}}</ref>

<ref name="discovery">{{cite web
| title = Discovery Circumstances: Numbered Minor Planets (90001)–(95000)
| publisher = IAU: Minor Planet Center
| url = http://www.minorplanetcenter.org/iau/lists/NumberedMPs090001.html
| access-date = 23 July 2008
| archive-date = 9 November 2017
| archive-url = https://web.archive.org/web/20171109081038/http://www.minorplanetcenter.org/iau/lists/NumberedMPs090001.html
| url-status = live
}}</ref>

<ref name="BannisterTwitter">
{{cite tweet
| first = Michelle
| last = Bannister
| user = astrokiwi
| author-link = Michele Bannister
| number = 978589989226401794
| date = 27 March 2018
| access-date = 27 March 2018
| title = #TNO2018
| quote = the census of dwarf planet satellites shows all the biggest systems seem to have satellites. Sedna isn't known to, but any satellite would spend at least a quarter of its time lost in Sedna's glare [...] no additional satellites for Makemake, Eris and OR10 down to 26th mag. Haumea has already been checked. Sedna the last remaining to double-check!
}}
</ref>

<ref name="HubbleProposal">{{cite web
| first = Michael E.
| last = Brown
| title = Characterization of a planetary-sized body in the inner Oort cloud – HST Proposal 10041
| url = https://archive.stsci.edu/proposal_search.php?id=10041&mission=hst
| date = 16 March 2004
| access-date = 27 March 2018
| archive-date = 4 May 2022
| archive-url = https://web.archive.org/web/20220504125534/https://archive.stsci.edu/proposal_search.php?id=10041&mission=hst
| url-status = live
}}</ref>

<ref name="Mystery">{{cite web
| url = http://hubblesite.org/news_release/news/2004-14
| title = Hubble Observes Planetoid Sedna, Mystery Deepens
| date = 14 April 2004
| access-date = 27 March 2018
| publisher = Space Telescope Science Institute
| archive-date = 29 March 2018
| archive-url = https://web.archive.org/web/20180329051953/http://hubblesite.org/news_release/news/2004-14
| url-status = live
}}</ref>

<ref name="DES">{{cite web
| first = Marc W.
| last = Buie
| author-link = Marc W. Buie
| date = 22 November 2009
| title = Orbit Fit and Astrometric record for 90377
| publisher = [[Deep Ecliptic Survey]]
| url = http://www.boulder.swri.edu/~buie/kbo/astrom/90377.html
| access-date = 17 January 2006
| archive-date = 20 May 2011
| archive-url = https://web.archive.org/web/20110520122821/http://www.boulder.swri.edu/~buie/kbo/astrom/90377.html
| url-status = live
}}</ref>

<ref name="jpldata">
{{cite web
 |type=2020-01-21 last obs 
 |title=JPL Small-Body Database Browser: 90377 Sedna (2003 VB12) 
 |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna 
 |archive-url=https://web.archive.org/web/20200227133304/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna
 |archive-date=27 February 2020
|url-status=live 
 |access-date=27 February 2020
}}
</ref>

<ref name="jpldata 2012 VP113">{{cite web
 |type=2013-10-30 last obs
 |title=JPL Small-Body Database Browser: (2012 VP113)
 |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012VP113
 |publisher=Jet Propulsion Laboratory
 |access-date=26 March 2014
|archive-date=9 June 2014
|archive-url=https://archive.today/20140609151034/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012VP113
 |url-status=live
 }}</ref>

<ref name="barycenter">{{cite web
 |author     = [[JPL Horizons On-Line Ephemeris System|Horizons]] output
 |url     = https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Sedna%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271900-01-01%27&STOP_TIME=%272500-01-01%27&STEP_SIZE=%27100%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27
 |title     = Barycentric Osculating Orbital Elements for 90377 Sedna (2003 VB12)
 |access-date     = 18 September 2021
|archive-date     = 17 October 2023
|archive-url     = https://web.archive.org/web/20231017202424/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Sedna%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271900-01-01%27&STOP_TIME=%272500-01-01%27&STEP_SIZE=%27100%20years%27&CENTER=%27%400%27&OUT_UNITS=%27AU-D%27
 |url-status     = live
 }} (Solution using the Solar System [[barycenter]]. Select Ephemeris Type:Elements and Center:@0) (Saved Horizons output file 2011-Feb-04 {{cite web |url=http://home.surewest.net/kheider/astro/sedna-bc.txt |title=Barycentric Osculating Orbital Elements for 90377 Sedna |url-status=dead |archive-url=https://web.archive.org/web/20121119041320/http://home.surewest.net/kheider/astro/sedna-bc.txt |archive-date=19 November 2012 }}) In the second pane "PR=" can be found, which gives the orbital period in days (4.160E+06, which is 11,390 [[Julian year (astronomy)|Julian years]]).</ref>

<ref name="largest">{{cite book
| chapter = The largest Kuiper belt objects
| title = The Solar System Beyond Neptune
| pages = 335–345
| editor1-first = M. Antonietta
| editor1-last = Barucci
| editor2-first = Hermann
| editor2-last = Boehnhardt
| editor3-first = Dale P.
| editor3-last = Cruikshank
| first = Michael E.
| last = Brown
| publisher = University of Arizona Press
| isbn = 978-0-8165-2755-7
| chapter-url = http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf
| year = 2008
| access-date = 19 September 2008
| archive-date = 13 November 2012
| archive-url = https://web.archive.org/web/20121113114533/http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf
| url-status = live
}}</ref>

<ref name="spitzer">{{cite book | title = The Solar System Beyond Neptune | chapter = Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope | first1 = John | last1 = Stansberry | first2 = Will | last2 = Grundy | first3 = Mike | last3 = Brown | first4 = Dale | last4 = Cruikshank | first5 = John | last5 = Spencer | first6 = David | last6 = Trilling | first7 = Jean-Luc | last7 = Margot | publisher = University of Arizona Press | chapter-url = http://www.lpi.usra.edu/books/ssbn2008/7017.pdf | arxiv = astro-ph/0702538v2 | editor1-first = M. Antonietta | editor1-last = Barucci | editor2-first = Hermann | editor2-last = Boehnhardt | editor3-first = Dale P. | editor3-last = Cruikshank | year = 2008 | isbn = 978-0-8165-2755-7 | pages = 161–179 | bibcode = 2008ssbn.book..161S | access-date = 15 August 2010 | archive-date = 25 October 2012 | archive-url = https://web.archive.org/web/20121025032659/http://www.lpi.usra.edu/books/ssbn2008/7017.pdf | url-status = live }}</ref>

<ref name="Tegler">
{{cite web
 |url         = http://www.physics.nau.edu/~tegler/research/survey.htm
 |title       = Kuiper Belt Object Magnitudes and Surface Colors
 |publisher   = Northern Arizona University
 |access-date  = 5 November 2006
|first      = Stephen C. | last=Tegler
 |date        = 26 January 2006
|url-status  = dead
 |archive-url  = https://web.archive.org/web/20060901063349/http://www.physics.nau.edu/~tegler/research/survey.htm
 |archive-date = 1 September 2006
}}
</ref>

<ref name="AstDys">{{cite web
 |title=AstDys (90377) Sedna Ephemerides
 |publisher=Department of Mathematics, University of Pisa, Italy
 |url=https://newton.spacedys.com/astdys/index.php?pc=1.1.3.1&n=90377&oc=500&y0=2023&m0=1&d0=1&y1=2024&m1=1&d1=1&ti=1.0&tiu=days
 |access-date=31 October 2023
|archive-date=31 October 2023
|archive-url=https://web.archive.org/web/20231031112839/https://newton.spacedys.com/astdys/index.php?pc=1.1.3.1&n=90377&oc=500&y0=2023&m0=1&d0=1&y1=2024&m1=1&d1=1&ti=1.0&tiu=days
 |url-status=live
 }}</ref>

<ref name="AstDys2003">{{cite web
 |title=AstDys (90377) Sedna Ephemerides 2003-11-14
 |publisher=Department of Mathematics, University of Pisa, Italy
 |url=https://newton.spacedys.com/astdys/index.php?n=90377&pc=1.1.4.1&oc=500&y0=2003&m0=11&d0=14&h0=00&mi0=00&s=3.0
 |access-date=6 July 2019
|archive-date=22 October 2023
|archive-url=https://web.archive.org/web/20231022074214/https://newton.spacedys.com/astdys/index.php?n=90377&pc=1.1.4.1&oc=500&y0=2003&m0=11&d0=14&h0=00&mi0=00&s=3.0
 |url-status=live
 }}</ref>

<ref name="Horizons2076">{{cite web 
 |url=http://home.surewest.net/kheider/astro/Sedna2076.txt 
 |title=Horizons Output for Sedna 2076/2114 
 |author=JPL Horizons On-Line Ephemeris System 
 |author-link=JPL Horizons On-Line Ephemeris System 
 |date=18 July 2010 |access-date=18 July 2010 |url-status=dead 
 |archive-url=https://web.archive.org/web/20120225015100/http://home.surewest.net/kheider/astro/Sedna2076.txt 
 |archive-date=25 February 2012 }} [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=Sedna Horizons] {{Webarchive|url=https://web.archive.org/web/20150912013053/http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=Sedna |date=12 September 2015 }}</ref>

<ref name="AstDyS2076">{{cite web
  |title=Sedna Ephemerides for July 2076
  |publisher=AstDyS
  |url=https://newton.spacedys.com/astdys/index.php?pc=1.1.3.1&n=90377&oc=500&y0=2076&m0=1&d0=1&y1=2076&m1=12&d1=1&ti=18&tiu=days
  |archive-url=https://web.archive.org/web/20210103145713/https://newton.spacedys.com/astdys/index.php?pc=1.1.3.1&n=90377&oc=500&y0=2076&m0=1&d0=1&y1=2076&m1=12&d1=1&ti=18&tiu=days
  |archive-date=3 January 2021 |url-status=live
  |access-date=31 December 2020}} ("R (au) column" is distance from Sun)</ref>

<ref name="Brown-dplist">
{{cite web
 |date=23 September 2011 |title=How many dwarf planets are there in the outer solar system? (updates daily) 
 |publisher=California Institute of Technology 
 |first=Michael E. | last=Brown 
 |author-link=Michael E. Brown 
 |url=http://www.gps.caltech.edu/~mbrown/dps.html 
 |access-date=23 September 2011 |url-status=dead 
 |archive-url=https://web.archive.org/web/20111018154917/http://www.gps.caltech.edu/~mbrown/dps.html 
 |archive-date=18 October 2011 }}
</ref>

<ref name="Tancredi2008">{{cite web
|year=2008
|title=Which are the dwarfs in the solar system?
|publisher=Asteroids, Comets, Meteors
|last1=Tancredi
|first1=G.
|last2=Favre
|first2=S.
|url=http://www.lpi.usra.edu/meetings/acm2008/pdf/8261.pdf
|access-date=5 January 2011
|archive-date=3 June 2016
|archive-url=https://web.archive.org/web/20160603215320/http://www.lpi.usra.edu/meetings/acm2008/pdf/8261.pdf
|url-status=live
}}</ref>

<ref name="fussman">
{{cite web
|title=The Man Who Finds Planets
|first=Cal | last=Fussman
|work=Discover
|url=http://discovermagazine.com/2006/may/cover
|year=2006
|access-date=22 May 2010
|archive-url= https://web.archive.org/web/20100616162058/http://discovermagazine.com/2006/may/cover |archive-date=16 June 2010 |url-status=live}}
</ref>

<ref name="Mike">
{{cite journal
|title=Discovery of a Candidate Inner Oort Cloud Planetoid
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<ref name="Perihelion2076">{{cite web
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  |publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]
  |type=Perihelion occurs when rdot flips from negative to positive
  |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Sedna%27&START_TIME=%272076-Jul-10%27&STOP_TIME=%272076-Jul-25%27&STEP_SIZE=%274%20hours%27&QUANTITIES=%2719%27
  |access-date=10 April 2021
|archive-date=11 April 2021
|archive-url=https://web.archive.org/web/20210411143556/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Sedna%27&START_TIME=%272076-Jul-10%27&STOP_TIME=%272076-Jul-25%27&STEP_SIZE=%274%20hours%27&QUANTITIES=%2719%27
  |url-status=live
  }} (JPL#34/Soln.date:  2021-Apr-13)</ref>

<ref name=McGranaghan>{{cite journal
 | last1=McGranaghan | first1=R.
 | last2=Sagan | first2=B.
 | last3=Dove | first3=G.
 | last4=Tullos | first4=A.
 | last5=Lyne | first5=J. E.
 | last6=Emery | first6=J. P.
 |date=2011
 |title=A Survey of Mission Opportunities to Trans-Neptunian Objects
 |journal=Journal of the British Interplanetary Society
 |volume=64 |pages=296–303 |bibcode=2011JBIS...64..296M}}
</ref>

<ref name="sednian">{{cite conference
 |url          = https://www.lpi.usra.edu/meetings/lpsc1990/pdf/1596.pdf
 |title        = Intermediate (20–100 KM ) Sized Volcanic Edifices on Venus
 |first1       = E. N.
 |last1        = Slyuta
 |first2       = M. A.
 |last2        = Kreslavsky
 |conference   = Lunar and planetary science XXI
 |year         = 1990
 |pages        = 1174
 |postscript   = (for [[Sedna Planitia]])
 |publisher    = Lunar and Planetary Institute
 |access-date  = 29 February 2020
|archive-date = 15 January 2021
|archive-url  = https://web.archive.org/web/20210115171933/https://www.lpi.usra.edu/meetings/lpsc1990/pdf/1596.pdf
 |url-status   = live
}}</ref>

<!--<ref name="Malhotra_Volk_Wang">{{cite journal
 | title=Corralling a distant planet with extreme resonant Kuiper belt objects
 | last1=Malhotra | first1=Renu | last2=Volk | first2=Kathryn
 | last3=Wang | first3=Xianyu
 | date=2016
 | journal=[[The Astrophysical Journal Letters]]
 | volume=824 | issue=2 | pages=L22
 | arxiv=1603.02196 | bibcode=2016ApJ...824L..22M
 | doi=10.3847/2041-8205/824/2/L22
}}</ref>
-->

<ref name=Chang_2016>{{cite news
 | last=Chang
 | first=Kenneth
 | url=https://www.nytimes.com/2016/01/21/science/space/ninth-planet-solar-system-beyond-pluto.html?emc=edit_au_20160120&nl=afternoonupdate&nlid=68634180&_r=0
 | title=Ninth Planet May Exist Beyond Pluto, Scientists Report
 | work=[[The New York Times]]
 | date=21 January 2016
| page=A1
 | access-date=1 March 2017
| archive-date=9 October 2016
| archive-url=https://web.archive.org/web/20161009204239/http://www.nytimes.com/2016/01/21/science/space/ninth-planet-solar-system-beyond-pluto.html?emc=edit_au_20160120&nl=afternoonupdate&nlid=68634180&_r=0
 | url-status=live
 }}</ref>

<ref name=Lakdawalla_2014>{{cite web
 | url=https://www.planetary.org/articles/03261345-a-second-sedna-what-does-it-mean
 | title=A second Sedna! What does it mean?
 | first=Emily
 | last=Lakdawalla
 | work=Planetary Society
 | date=26 March 2014
| access-date=1 April 2023
 | archive-date=10 December 2018
| archive-url=https://web.archive.org/web/20181210092331/http://www.planetary.org/blogs/emily-lakdawalla/2014/03261345-a-second-sedna-what-does-it-mean.html
 | url-status=live
 }}</ref>

<ref name="Evidence for a Distant Giant Planet">{{cite journal
 | title=Evidence for a Distant Giant Planet in the Solar System
 | last1=Batygin | first1=Konstantin | last2=Brown | first2=Michael E.
 | journal=[[The Astronomical Journal]]
 | date=2016 | volume=151 | issue=2 | page=22
 | doi=10.3847/0004-6256/151/2/22 | arxiv=1601.05438
 | bibcode=2016AJ....151...22B | s2cid=2701020
| doi-access=free }}</ref>

<ref name="Emery2024">{{cite journal |last1=Emery |first1=J. P. |last2=Wong |first2=I. |last3=Brunetto |first3=R. |last4=Cook |first4=J. C. |last5=Pinilla-Alonso |first5=N. |last6=Stansberry |first6=J. A. |last7=Holler |first7=B. J. |last8=Grundy |first8=W. M. |last9=Protopapa |first9=S. |last10=Souza-Feliciano |first10=A. C. |last11=Fernández-Valenzuela |first11=E. |last12=Lunine |first12=J. I. |last13=Hines |first13=D. C. |title=A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy |journal=Icarus |date=2024 |volume=414 |doi=10.1016/j.icarus.2024.116017 |arxiv=2309.15230|bibcode=2024Icar..41416017E }}</ref>

}} <!-- end of reflist -->

==Further reading==
{{Div col|small=yes}}
*{{cite journal
 | title=A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy
 | first1=J. P. | last1=Emery | first2=I. | last2=Wong
 | 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 | date=2024 | volume=414 | doi=10.1016/j.icarus.2024.116017 | arxiv=2309.15230 | bibcode=2024Icar..41416017E }}
*{{cite news
 | title=NASA To Sedna? The 'Pluto-Killing' World That Orbits Our Sun Every 11,408 Years Is Almost In Range Say Scientists
 | first=Jamie | last=Carter | date=4 January 2022
| work=Forbes
 | url=https://www.forbes.com/sites/jamiecartereurope/2022/01/04/nasa-to-sedna-the-pluto-killing-world-that-orbits-our-sun-every-11408-years-is-almost-in-range-say-scientists/
 | access-date=15 January 2023 }}
*{{cite journal
 | title=Analysis of optimal flight trajectories to the Trans-Neptunian Object (90377) Sedna
 | first1=V. A. | last1=Zubko | first2=A. A. | last2=Sukhanov
 | first3=K. S. | last3=Fedyaev | first4=V. V. | last4=Koryanov
 | first5=A. A. | last5=Belyaev 
 | journal=Astronomy Letters
 | volume=47 | pages=188–195 | year=2021
 | issue=3 | bibcode=2021AstL...47..188Z | doi=10.1134/S1063773721030087 | s2cid=255195476 }}
*{{cite journal
 | title=Getting to Sedna and Eris Using Solar Electric Propulsion
 | last1=Bering | first1=E. A. | last2=Giambusso | first2=M.
 | last3=Parker | first3=A. H. | last4=Carter | first4=M.
 | last5=Squire | first5=J. P. | last6=Chang Díaz | first6=F. R.
 | journal=51st Lunar and Planetary Science Conference, Held 16–20 March 2020 at the Woodlands, Texas. LPI Contribution No. 2326
 | id=2050 | date=March 2020 | issue=2326 | page=2050 | bibcode=2020LPI....51.2050B }}
*{{cite journal
 | title=Sedna and the cloud of comets surrounding the solar system in Milgromian dynamics
 | last1=Paučo | first1=R. | last2=Klačka | first2=J.
 | journal=Astronomy & Astrophysics
 | volume=589 | id=A63 | date=May 2016
 | pages=A63 | doi=10.1051/0004-6361/201527713 | arxiv=1602.03151
 | bibcode=2016A&A...589A..63P }}
*{{cite journal
 | title=How Sedna and family were captured in a close encounter with a solar sibling
 | first1=Lucie | last1=Jílková | first2=Simon Portegies | last2=Zwart
 | first3=Tjibaria | last3=Pijloo | first4=Michael | last4=Hammer
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=453 | issue=3 | date=1 November 2015 | pages=3157–3162
 | orig-year=9 June 2015
 | arxiv=1506.03105 |doi=10.1093/mnras/stv1803
 | doi-access=free | bibcode=2015MNRAS.453.3157J |s2cid=119188358 }}
{{Div col end}}

== External links ==
{{Spoken Wikipedia|En-90377_Sedna-article.ogg|date=30 January 2014}}
{{Commons and category|Sedna}}
* [https://www.nasa.gov/vision/universe/solarsystem/planet_like_body.html NASA's Sedna page]. {{Webarchive|url=https://web.archive.org/web/20180314041910/https://www.nasa.gov/vision/universe/solarsystem/planet_like_body.html |date=14 March 2018 }} (Discovery Photos).
* [http://web.gps.caltech.edu/~mbrown/sedna/ Mike Brown's Sedna page]
* {{JPL small body|id=90377}}

{{Minor planets navigator |90376 Kossuth |number=90377 | }}
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[[Category:Sednoids|S]]
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[[Category:Inner Oort cloud]]
[[Category:Named minor planets|Sedna]]
[[Category:Dwarf planets|Sedna]]
[[Category:Astronomical objects discovered in 2003|20031114]]
[[Category:Discoveries by Chad Trujillo|Sedna]]
[[Category:Discoveries by David L. Rabinowitz|Sedna]]
[[Category:Discoveries by Michael E. Brown|Sedna]]
[[Category:Scattered disc and detached objects]]
[[Category:Solar System]]