View source for 99942 Apophis

{{Short description|Potentially hazardous near-Earth asteroid}}
{{Use mdy dates|date=December 2024}}
{{Infobox planet
| background = #FFC2E0
| discoverer = {{Ubl
 | [[Roy A. Tucker]]
 | [[David J. Tholen]]
 | [[Fabrizio Bernardi]]
 }}
| discovery_site = [[Kitt Peak National Observatory|Kitt Peak]]<ref name="jpldata"/>
| minorplanet = yes
| name = 99942 Apophis
| symbol = [[file:Apophis symbol (bold).svg|24px]] (rare)
| image = 99942 Apophis shape.png
| image_scale = 
| caption = Model of 99942 Apophis's shape, assuming the entire surface is of a similar composition
| discovery_ref = <ref name="jpldata"/>
| discovered = June 19, 2004
| earliest_precovery_date = March 15, 2004
| mpc_name = (99942) Apophis
| pronounced = {{IPAc-en|ə|ˈ|p|ɒ|f|ɪ|s}} or {{IPAc-en|ə|ˈ|p|oʊ|f|ɪ|s}}; (trad.) {{IPAc-en|ˈ|æ|p|ə|f|ɪ|s}}
| adjective = Apophidian {{IPAc-en|æ|p|ə|ˈ|f|ɪ|d|i|ə|n}} (Latin ''Apŏpidis'')
| alt_names = {{mp|2004 MN|4}}
| named_after = [[Apep|Ἄποφις]] ''Apophis''
| mp_category = {{Hlist
 | [[Aten asteroids|Aten]]
 | [[Near-Earth object|NEO]]
 | [[Potentially hazardous object|PHA]]<ref name="jpldata"/>
 }}
| orbit_ref = <ref name="jpldata"/>
| epoch = September&nbsp;13, 2023<br/>([[Julian day|JD]]&nbsp;2453300.5)
| uncertainty = 0
| observation_arc = 6267 days (17.16&nbsp;yr)
| aphelion = {{Convert|1.0994|AU|e6km|abbr=unit|lk=on}}
| period = 0.886&nbsp;[[Julian year (astronomy)|yr]] (323.7&nbsp;[[Julian day (astronomy)|d]])
| mean_orbit_radius = {{Convert|0.9225|AU|e6km|abbr=unit}}
| semimajor = {{Convert|0.9227|AU|e6km|abbr=unit}}
| perihelion = {{Convert|0.7461|AU|e6km|abbr=unit}}
| eccentricity = 0.19144
| inclination = 3.339[[Degree (angle)|°]]
| asc_node = 203.96°
| arg_peri = 126.60°
| avg_speed = 30.73&nbsp;km/[[second|s]]
| mean_anomaly = 142.9°
| mean_motion = 1.11198°/day
| moid = Less than {{Convert|0.0007|AU|e3km|abbr=unit}}<ref name="jpldata"/>{{efn|The MOID is changing. In the JPL reference the value of 0.000612759 AU is given, for November 2023, but in early 2029 it will be only around 0.00006 AU (ca 9480 km).<ref name="Farnocchia2013_Icarus"/>}}
| jupiter_moid = 
| tisserand = 6.464
| abs_magnitude = {{Ubl
 | {{val|19.7|0.4}}<ref name="jpldata"/><ref name="phys"/>
 | {{val|19.09|0.19}}<ref name="Brozovic2018"/>
 | {{val|18.95|0.15}}<ref name="Neodys_eq1"/>
 }}
| dimensions = {{Ubl
 | {{Convert|0.370|km|abbr=on}}
 | 0.45&thinsp;×&thinsp;0.17&nbsp;km<ref name="Brozovic2018"/>
 }}
| mean_radius = {{Ubl
 | {{Convert|0.185|km|abbr=on}}
 | {{val|0.17|0.02|u=km}}<ref name="Brozovic2018"/>
 }}
| density = {{Ubl
 | ~3.2&nbsp;g/cm{{sup|3}}<ref name="Binzel2007"/>
 | 2.6&nbsp;g/cm{{sup|3}} (assumed)<ref name="riskneo"/>
 }}
| mass = {{Val|6.1e10|u=kg}} (assumed)<ref name="riskneo"/>
| rotation = {{Convert|30.4|h|d|abbr=on|lk=on}}<ref name="jpldata"/><ref name="phys"/><br />30.55±0.12&nbsp;h<ref name="Reddy2022"/><br />30.67±0.06&nbsp;h<ref name="IAWN2021-Gallery"/><br />[[Tumbling asteroid|Tumbling]]:<ref name=“tumblingspinstate”/><br />27.38±0.07&nbsp;h (precession period),<ref name=“tumblingspinstate”/> 263±6&nbsp;h (rotation period),<ref name=“tumblingspinstate”/> 30.56±0.01&nbsp;h (twice the period of harmonic with strongest lightcurve amplitude)<ref name=“tumblingspinstate”/>
| spectral_type = Sq<ref name="phys"/>
| albedo = {{Ubl
 | 0.23<ref name=“esanews1”/>
 | {{val|0.35|0.10}}<ref name="Brozovic2018"/>
 }}
| single_temperature = 270 [[kelvin|K]]
}}

'''99942 Apophis''' ([[Minor planet provisional designation|provisional designation]] '''{{mp|2004 MN|4}}''') is a [[Near-Earth asteroids|near-Earth asteroid]] and a [[potentially hazardous object]], {{Convert|450|metres|ft}} by {{Convert|170|metres|ft}} in size,<ref name="Brozovic2018"/> that caused a brief period of concern in December 2004 when initial observations indicated a probability of 2.7% that it would hit [[Earth]] on Friday, April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an [[impact event|impact on Earth]] in 2029. A small possibility nevertheless remained that, during its 2029 close encounter with Earth, Apophis would pass through a [[gravitational keyhole]] estimated to be 800 metres in diameter,<ref name=“keyhole”/><ref name="Neil deGrasse Tyson – Death By Giant Meteor"/> which would have set up a future impact exactly seven years later on Easter Sunday, April&nbsp;13, 2036.<ref name="“Predicting”">{{cite journal |last1=Giorgini |first1=Jon |display-authors=etal |date=October 4, 2007 |title=Predicting the Earth encounters of (99942) Apophis |url=http://neo.jpl.nasa.gov/apophis/Apophis_PUBLISHED_PAPER.pdf |url-status=dead |journal=Icarus |volume=193 |pages=1–19 |doi=10.1016/j.icarus.2007.09.012 |archive-url=https://web.archive.org/web/20161222041852/http://neo.jpl.nasa.gov/apophis/Apophis_PUBLISHED_PAPER.pdf |archive-date=December 22, 2016}}</ref> This possibility kept it at Level&nbsp;1 on the [[Torino scale|Torino impact hazard scale]] until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis's rating on the Torino scale was lowered to zero. By 2008, the keyhole had been determined to be less than 1&nbsp;km wide.<ref name=“keyhole”/> During the short time when it had been of greatest concern, Apophis set the record for highest rating ever on the Torino scale, reaching level&nbsp;4 on December 27, 2004.<ref name="nasanews146"/>

The discovery of Apophis in 2004 is rather surprising because it is estimated that an asteroid as big or bigger coming so close to Earth happens only once in 800 years on average.<ref name="neo"/><ref name=“Predicting”/> Such an asteroid is expected to actually hit Earth once in about 80,000 years.<ref name="Earth-impact"/>

Preliminary observations by [[Goldstone Deep Space Communications Complex|Goldstone]] radar in January 2013 effectively ruled out the possibility of an Earth impact by Apophis in 2036 (probability less than 1 in a million).<ref name="NASA2013-017"/> In February 2013 the estimated probability of an impact in 2036 was reduced to {{value|7|e=-9}}.<ref name="Farnocchia2013_Icarus"/><ref name="riskneo"/> It is now known that in 2036, Apophis will approach the Earth at a third the distance of the Sun in both March and December,<ref name="jpldata"/>{{dash}}this is about the distance of the planet [[Venus]] when it overtakes Earth every 1.6 years. Simulations in 2013 showed that the [[Yarkovsky effect]] might cause Apophis to hit a "keyhole" in 2029 so that it will come close to Earth in 2051, and then could hit another keyhole and hit Earth in 2068. But the chance of the Yarkovsky effect having exactly the right value for this was estimated as 2 in a million.<ref name="Farnocchia2013_Icarus"/><ref name="S&T2020"/> Radar observations in March 2021 helped to refine the orbit,<ref name="Goldstone2021"/> and in March 2021 the [[Jet Propulsion Laboratory]] announced that Apophis has no chance of impacting Earth in the next 100 years.<ref>{{cite web|url=https://www.jpl.nasa.gov/news/nasa-analysis-earth-is-safe-from-asteroid-apophis-for-100-plus-years|title=NASA Analysis: Earth Is Safe From Asteroid Apophis for 100-Plus Years|date=March 25, 2021|publisher=Jet Propulsion Laboratory}}</ref><ref>{{Cite web|last=Hurst|first=Luke|date=March 28, 2021|title=Asteroid Apophis won't hit Earth for at least 100 years, says NASA|url=https://www.euronews.com/2021/03/28/good-news-asteroid-apophis-won-t-hit-earth-for-at-least-100-years-says-nasa|access-date=April 2, 2021|website=euronews}}</ref> The uncertainty in the 2029 approach distance has been reduced from hundreds of kilometres to now just a couple of kilometres,<ref name="Horizons2029"/> greatly enhancing predictions of future approaches. Entering March 2021, six asteroids each had a more notable cumulative [[Palermo scale]] rating than Apophis, and none of those has a Torino level above 0.<ref name="risk-table"/>{{efn|name=palermo}} However, Apophis will continue to be a threat possibly for thousands of years until it is removed from being a potentially hazardous object, for instance by passing close to Venus or Mars.

== Discovery and naming ==
[[File:PIA23195-AsteroidApophis-ClosestApproachToEarth-20190429.webm|thumb|upright=3|center|<div align="center">Asteroid Apophis{{Snd}}closest approach to Earth on April 13, 2029<ref name="NASA-20190429"/><br /><small>(00:20; [[:File:PIA23195-AsteroidApophis-ClosestApproachToEarth-20190429.webm|VideoFile]]; April 29, 2019) (turquoise dots = [[Satellite|artificial satellites]]; pink = [[International Space Station]])</small></div>]]
Apophis was discovered on June 19, 2004, by [[Roy A. Tucker]], [[David J. Tholen]], and [[Fabrizio Bernardi]] at the [[Kitt Peak National Observatory]].<ref name="jpldata"/> On December 21, 2004, Apophis passed {{convert|0.0964|AU|Gm e6mi|abbr=unit|lk=on}} from Earth.<ref name="jpldata"/> [[Precovery]] observations from March 15, 2004, were identified on December&nbsp;27, and an improved orbit solution was computed.<ref name="MPEC2004-Y70"/><ref name="nasanews148"/> [[Radar astronomy|Radar]] astrometry in January 2005 further refined its orbit solution.<ref name=“Arecibo”/><ref name="nasanews149"/> The discovery was notable in that it was at a very low [[Elongation (astronomy)|solar elongation]] (56°) and at very long range (1.1&nbsp;AU).{{citation needed|date=January 2024}}

When first discovered, the object received the provisional designation {{mp|2004 MN|4}}, and early news and scientific articles naturally referred to it by that name. Once its orbit was sufficiently well calculated, it received the permanent number 99942 (on June&nbsp;24, 2005). Receiving a permanent number made it eligible for naming by its discoverers, and they chose the name "Apophis" on July&nbsp;19, 2005.<ref name=“naming”/> Apophis is the [[Greek language|Greek]] name of [[Apep]], an enemy of the [[Ancient Egypt]]ian sun-god [[Ra]]. He is the Uncreator, an evil serpent that dwells in the eternal darkness of the [[Duat]] and tries to swallow Ra during his nightly passage. Apep is held at bay by [[Set (deity)|Set]], the Ancient Egyptian god of storms and the desert.<ref>{{Cite web|url=https://ancientegyptonline.co.uk/apep/|title=Apep (Apophis)|publisher=Ancient Egypt Online|author=Hill, J.|year=2010|access-date=July 24, 2021}}</ref>
[[File:Apep 1.jpg|thumb|upright=1.2|[[Atum]] facing Apep, [[KV16|tomb of Ramesses I]], 19th Dynasty (c. 1292–1290 BC)]]
Tholen and Tucker, two of the co-discoverers of the asteroid, are reportedly fans of the television series ''[[Stargate SG-1]]''. One of the show's persistent villains is an alien named [[Goa'uld characters in Stargate#Apophis|Apophis]]. He is one of the principal threats to the existence of civilization on Earth through the first few seasons, thus likely why the asteroid was named after him. In the fictional world of the show, the alien's backstory was that he had lived on Earth during ancient times and had posed as a god, thereby giving rise to the myth of the Egyptian god of the same name.<ref name=“naming”/>

[[File:Apophis symbol (fixed width).svg|thumb|left|80px|Proposed symbol for Apophis]]
The mythological creature Apophis is pronounced with the accent on the first syllable (/ˈæpəfɪs/).{{efn|This is normal for classical names in which the penultimate syllable is short.}} In contrast, the asteroid's name is generally accented on the second syllable ({{IPA|/əˈpoʊfɪs/}},<ref>{{dict.com|Apophis}}</ref> or {{IPA|/əˈpɒfɪs/}} as the name was pronounced in the TV series).<ref name="pronunciation1">As an example, here is David Tholen, the discoverer of the asteroid, pronouncing the name: {{cite web|url=https://www.youtube.com/watch?t=1307&v=AfE87Pi3SqE|title=DPS 52 Monday Press Conference|publisher=AAS Press Office|date=October 26, 2020|via=YouTube}}</ref>

[[Planetary symbol|Symbols]] were given to the first few asteroids in the 19th century, though this practice faded when it became clear that there were a great number of them, and such symbols are now extremely rarely used by astronomers. In 2008, Denis Moskowitz, a software engineer who devised most of the [[dwarf planet]] symbols in [[Unicode]], proposed a symbol for Apophis. His symbol is based on ancient Egyptian depictions of Apep. The added star is similar to many of the 19th-century asteroid symbols.<ref>{{cite book|last1=Finlay|first1=Alec|last2=Sharples|first2=Ray|last3=Moskowitz|first3=Denis|title=One Hundred Year Star-Diary: 2008-2107|publisher=Platform Projects/Morning Star|isbn=9780955202711|oclc=316730683|date=April 24, 2008}}</ref><ref>{{cite web|title=Symbols for One Hundred Year Star-Diary|first=Alec|last=Finlay|publisher=Kielder Observatory Astronomical Society|url=https://suberic.net/~dmm/astro/diary.html|date=April 2, 2008|archive-url=https://web.archive.org/web/20081012183213/https://suberic.net/~dmm/astro/diary.html|archive-date=October 12, 2008|url-status=live}}</ref>

== Physical characteristics and rotation ==

[[File:Apophis model comparison.png|thumb|upright=1.2|Comparison between the best-fit convex and nonconvex shape models, and some of the available radar images of (99942) Apophis]]

[[File:Size of Apophis asteroid.png|left|thumb|Comparison of possible size of Apophis asteroid with the [[Eiffel Tower]] and [[Empire State Building]]]]

Based on the observed brightness, Apophis's diameter was initially estimated at {{convert|450|m}}; a more refined estimate based on spectroscopic observations at [[NASA]]'s [[Infrared Telescope Facility]] in Hawaii by Binzel, Rivkin, Bus, and Tokunaga (2005) is {{convert|350|m}}. As of 2013, NASA's impact risk page listed the diameter at {{convert|330|m}}, and an assumed mass of 4{{e|10}} kg.<ref name="riskneo"/> The mass estimate is more approximate than the diameter estimate, but should be accurate to within a factor of three.<ref name="riskneo"/> Apophis's surface composition probably matches that of [[LL chondrite]]s.<ref name=“Reddy2018”/>

Based on Goldstone and Arecibo radar images taken in 2012–2013, [[Marina Brozović|Brozović]] et al. have estimated that Apophis is an elongated object 450&thinsp;×&thinsp;170 metres in size, and that it is bilobed (possibly a [[Contact binary (small Solar System body)|contact binary]]) with a relatively bright surface albedo of {{val|0.35|0.10}}. The axis of its angular momentum points 59° south of the [[ecliptic]], which means that Apophis is a [[retrograde rotation|retrograde rotator]].<ref name="Brozovic2018"/> Apophis is a [[Tumbling asteroid|tumbler]], which means that it does not rotate around a fixed axis. Rather, the axis of rotation moves in the frame of reference of the asteroid with a period of around 263 hours (called the rotation period). The angle between it and the [[principal axis (mechanics)|principal axis]] of highest [[moment of inertia]] varies, as does the angle between that principal axis and the vector of angular momentum (from around 12° to around 55° twice every period). During this period, the angle between the long axis of Apophis and the angular momentum vector swings between around 78° and 102° (90°±12°). But the principal axis of highest moment and the rotation axis both move around the constant axis of angular momentum much faster, with a time-averaged period of 27.38 hours (this is called [[precession]]). The result is that Apophis appears to be flipping, making a revolution on average every 30.56 hours. Every 263 hours, the principal axis with highest moment goes around 263/27.28 times (ca 9.6), whereas the long axis goes around 263/30.56 times (ca 8.6).<ref name=“tumblingspinstate”/>

== Orbit ==
[[File:Change in orbit of Apophis in 2029.png|thumb|upright=1.8|The pre-2029 (red) and post-2029 (green) orbits of Apophis, and the orbit of Earth (yellow). The distance between the dotted curve and the solid curve shows how far the orbit is north or south of the [[ecliptic plane]]. This gives the distance from Earth's orbit at the points where the solid curves cross the yellow curve.]]
Apophis has a low inclination orbit (3.3°) that varies from just outside the orbit of [[Venus]] (0.746 AU, as compared to the aphelion of Venus, 0.728) to just outside the orbit of [[Earth]] (1.099 AU).<ref name="jpldata"/> Although its orbit changes slightly each time it comes close to the earth, at present it comes near Earth once in 7.75 years on average (four times between April 14, 1998, and April 13, 2029). Because of its eccentric orbit, these moments are not evenly spaced and tend to occur between December and April (when Apophis is in the outer portions of its orbit).<ref name=“Predicting”/> In fact, the eccentricity and semi-major axis are such that (before 2029) Apophis is always receding from Earth around May 1 and is always approaching around December 2.<ref>See "deldot" in [https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=apophis&START_TIME=%271900-5-1%27&STOP_TIME=%272029-4-25%27&STEP_SIZE=%271%20years%27&QUANTITIES=%2718%2019%2020%2031 this JPL Horizons simulation] and [https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=apophis&START_TIME=%271900-12-2%27&STOP_TIME=%272029-4-25%27&STEP_SIZE=%271%20years%27&QUANTITIES=%2718%2019%2020%2031 this one].</ref> At the [[ascending node]] (where Apophis crosses the plane of the earth's orbit from south to north) Apophis is very close to where Earth is around April 13 of any year, and this is what gives rise to close encounters such as the one on April 13, 2029. The orbit also passes south of where the earth is in mid December, producing for example the close approaches of December 16, 1889, and December 18, 1939.<ref name=“Predicting”/> After the 2029 Earth approach, the orbit will change dramatically. The period will change from around {{frac|8|9}} of a year to a bit under {{frac|7|6}}. It will still come very close to Earth's yearly April 13 location. It will no longer pass close to Earth's yearly mid-December location, but will now pass close to Earth's mid-September location. This will cause a close encounter on September 11, 2102, after which the uncertainty in the location of Apophis will increase rapidly with time.<ref name="jpldata"/>

{| class="wikitable sortable" style="font-size: 0.9em;"
|+Selected approaches to Earth till 2117<ref name="jpldata"/>
! Date
! [[JPL SBDB]]<br />[[Curve fitting|nominal]] geocentric<br />distance ([[astronomical unit|AU]])
!class=unsortable| uncertainty<br />region<br />([[3-sigma]])
|-
|2004-12-21 ||{{Convert|0.09638|AU|e6km|abbr=unit}} || n/a 
|-
|2013-01-09 ||{{Convert|0.09666|AU|e6km|abbr=unit}} || n/a 
|-
|2029-04-13 ||{{Convert|0.000254115|AU|km|abbr=unit}} || ±3.3&nbsp;km<ref name="Horizons2029"/>
|-
|2036-03-27 ||{{Convert|0.309678|AU|e6km|abbr=unit}} || ±130 thousand km<ref name="Horizons2036"/>
|-
|2051-04-20 ||{{Convert|0.04149|AU|e6km|abbr=unit}} || ±250 thousand km
|-
|2066-09-16 ||{{Convert|0.06943|AU|e6km|abbr=unit}} || ±870 thousand km
|-
|2116-04-12 ||{{Convert|0.01756|AU|e6km|abbr=unit}} || {{convert|0.00104|to|0.10433|AU|e6km|abbr=unit}} {{efn|The minimum possible Earth approach between April 5–20, 2116 is {{convert|0.00102|AU|e3km|abbr=unit|lk=off}}. "JPL Horizons" gives 13 million km for 3σ<ref name="Horizons2116"/>}}
|-
|2117-10-07 ||{{Convert|0.48|AU|e6km|abbr=unit}} || {{convert|0.30994|to|0.64045|AU|e6km|abbr=unit}} {{efn|"JPL Horizons" gives 42 million km for 3σ<ref name="Horizons2117"/>}}
|}

=== 2029 close approach ===
The closest known approach of Apophis will occur on April&nbsp;13, 2029, at 21:46 [[Universal Time|UT]], when Apophis will pass Earth at a distance of about {{convert|31600|km|lk=on}} above the surface.<ref name=“surface”>2029-Apr-13 approach: {{Convert|0.000254093|AU|km|abbr=on|lk=on}}. [https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Apophis&view=OPC 38012km "geocentric distance"] – 6378km "[[Earth radius]]" = 31634km</ref><ref name=“blog2023”>{{Cite web|url=https://blogs.nasa.gov/osiris-rex/2023/09/24/osiris-rex-spacecraft-departs-for-new-mission/|title=OSIRIS-REx Spacecraft Departs for New Mission|date=September 24, 2023}}</ref> Using the June 2021 orbit solution which includes the [[Yarkovsky effect]], the [[3-sigma]] uncertainty region in the 2029 approach distance is about ±3.4&nbsp;km.<ref name="Horizons2029"/><ref name="jpldata"/> The distance, a hair's breadth in astronomical terms, is five times the [[Earth radius|radius of the Earth]], one tenth the distance to the [[Moon]],<ref name=“blog2023”/> and closer than the ring of [[geostationary]] satellites currently orbiting the Earth.<ref>{{Cite web|url=https://www.satsig.net/sslist.htm|title=List of satellites in geostationary orbit|website=satsig.net}}</ref><ref name="earthsky-preparing"/> It will be the closest asteroid of its size in recorded history. On that date, it will become as bright as magnitude&nbsp;3.1<ref name="NEODyS2029"/> (visible to the [[naked eye]] from rural as well as darker suburban areas, visible with [[binoculars]] from most locations).<ref name="mag-scale"/> The close approach will be visible from [[Europe]], [[Africa]], and western [[Asia]]. Over the course of about a day, Apophis will move northwest from [[Centaurus]] to [[Perseus (constellation)|Perseus]] and then southwest to [[Pisces (constellation)|Pisces]], an arc of 205°.<ref>From [[ecliptic longitude]] and latitude of 221°, −16° to 16°, 12° (according to [https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=apophis&START_TIME=%272029-4-1%27&STOP_TIME=%272029-4-25%27&STEP_SIZE=%271%20days%27&QUANTITIES=%2718%2019%2020%2031 this Horizons run]), or in [[right ascension]] and [[declination]], from 14h14m, −30°17' to 0h39m, 16°51' (using [https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=apophis&START_TIME=%272029-4-1%27&STOP_TIME=%272029-4-25%27&STEP_SIZE=%271%20days%27&QUANTITIES=2 this]).</ref> During the approach, Earth will [[Perturbation (astronomy)|perturb]] Apophis from an [[Aten asteroid|Aten]]-class orbit with a [[semi-major axis]] of 0.92&nbsp;[[Astronomical unit|AU]] to an [[Apollo asteroid|Apollo]]-class orbit with a semi-major axis of 1.1&nbsp;AU.<ref name="Orbit2029"/> [[Perihelion]] will lift from 0.746&nbsp;AU to 0.895&nbsp;AU and aphelion will lift from 1.10&nbsp;AU to 1.31&nbsp;AU.<ref name="Orbit2029"/>

{| class=wikitable style="font-size: 0.9em;"
|+Orbital elements for 2029 (pre-flyby) and 2030 (post-flyby)<ref name="Orbit2029"/>
|- valign=top
! Parameter
! [[Epoch (astronomy)|Epoch]]
! Orbit<br />type
! [[Orbital period|Orbital<br/>period]]
! [[Semi-major axis|Semi-major<br />axis]]
! [[Apsis|Perihelion]]
! [[Apsis|Aphelion]]
! [[Orbital inclination|Inclination]]
! [[Orbital eccentricity|Eccentricity]]
|- valign=top
! Units
!
!
!
!colspan=3|[[Astronomical unit|AU]]
!(°)
!
|- align=center
| Pre-flyby
| 2029
| [[Aten asteroid|Aten]]
| {{convert|323.6|days|years|abbr=off|sigfig=2|order=flip}}
| 0.922
| 0.746
| 1.10
| 3.34°
| 0.191
|- align=center
| Post-flyby
| 2030
| [[Apollo asteroid|Apollo]]
| {{convert|423.1|days|years|abbr=off|sigfig=3|order=flip}}
| 1.103
| 0.895
| 1.31
| 2.22°
| 0.189
|}

{{multiple image
| align = left
| direction = horizontal
| width = 300
| image1 = Animation of 99942 Apophis orbit around Sun.gif
| caption1 = Around Sun
| image2 = Animation of 99942 Apophis orbit around Earth.gif
| caption2 = Around Earth
| footer ={{legend2| yellow| Sun}}{{·}}{{legend2| RoyalBlue| Earth}}{{·}}{{legend2| Magenta| 99942 Apophis }}{{·}}{{legend2| Gold| Moon}}
| header = Animation of 99942 Apophis orbit in 2028–2029
}}

During the 2029 approach, Apophis's brightness will peak at [[apparent magnitude|magnitude]]&nbsp;3.1,<ref name="NEODyS2029"/> easily visible to the naked eye, with a maximum angular speed of 42° per hour. The maximum apparent [[angular diameter]] will be approximately 2&nbsp;[[arcsecond]]s. This is roughly equivalent to the [[angular diameter]] of [[Neptune]] from earth. Therefore, the asteroid will be barely [[optical resolution|resolved]] by ground-based telescopes not equipped with [[adaptive optics]] but very well resolved by those that are.<ref name = NeptuneVLTAdaptiveOptics/> Because the approach will be so close, [[tide|tidal forces]] are likely to alter Apophis's rotation axis, but Apophis will not approach within the [[Roche limit]] where it would be broken up by tidal forces. A partial resurfacing of the asteroid is possible, which might change its spectral class from a [[Space weathering|weathered]] Sq- to an unweathered [[Q-type asteroid|Q-type]].<ref name="Brozovic2018"/><ref name=“Reddy2018”/>
{{Clear}}

{{Large near earth asteroid flybys 2LD}}

=== 2036 approaches ===
In 2036, Apophis will pass the Earth at a third the distance of the Sun in both March and December.<ref name="jpldata"/> Using the 2024 orbit solution, the Earth approach on March 27, 2036, will be no closer than {{convert|0.3089|AU|e6km e6mi LD|abbr=unit|lk=in}}, but more likely about {{convert|0.3097|AU|e6km e6mi|abbr=unit}}.<ref name="jpldata"/> For comparison, the planet Venus will be closer to Earth at {{convert|0.2883|AU|e6km e6mi LD|abbr=unit|lk=off}} on May 30, 2036.<ref name=“Venus”>{{Cite web|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27299%27&START_TIME=%272036-05-30%2002:10%27&STOP_TIME=%272036-05-30%2002:30%27&STEP_SIZE=%271%20min%27&QUANTITIES=%2720%27|title=Venus 2036-May-30 @ JPL Horizons}}</ref>{{efn|name=Venus2022}} On December 31, 2036, Apophis will be a little bit further away than the March approach at about {{convert|0.33|AU|e6km e6mi|abbr=unit}}.

=== 2051 approach ===
Around April 19–20, 2051, Apophis will pass about {{convert|0.04|AU|e6km e6mi|abbr=unit|lk=off}} from Earth and it will be the first time since 2029 that Apophis will pass within 10 million km of Earth.<ref name="jpldata"/>

=== 2066 and 2068 ===

Although early simulations showed that there was a chance Apophis could hit the earth on April 12, 2068,<ref name="Farnocchia2013_Icarus"/> this was later excluded and [[JPL Horizons On-Line Ephemeris System|JPL Horizons]] calculates that Apophis will be about {{convert|1.864|+/-|0.003|AU|e6km|abbr=unit|lk=off}} from Earth,<ref name="Horizons2068"/><ref name="NEODyS2068"/> making the asteroid much farther than the Sun.

By 2116, the [[JPL Small-Body Database]] and [[NEODyS]] close approach data start to become [[Chaos theory|divergent]].<ref name="jpldata"/><ref name=“NEODys”/> In April 2116, Apophis is expected to pass about {{convert|0.02|AU|e6km LD|abbr=unit|sigfig=1}} from Earth, but could pass as close as {{convert|0.001|AU|e3km LD|abbr=unit}} or as far as {{convert|0.1|AU|e6km LD|abbr=unit}}.<ref name="jpldata"/>

=== Refinement of close approach predictions ===
Six months after discovery, and shortly after a close approach to Earth on December 21, 2004, the improved orbital estimates led to the prediction of a very close approach on April 13, 2029, by both NASA's automatic [[Sentry (monitoring system)|Sentry]] system and [[NEODyS]], a similar automatic program run by the [[University of Pisa]] and the [[University of Valladolid]]. Subsequent observations decreased the uncertainty in Apophis's trajectory and the probability of an impact event in 2029 temporarily climbed, peaking at 2.7% (1 in 37) on December 27, 2004,<ref name="nasanews164"/><ref name="mirror"/> when the uncertainty region had shrunk to 83,000&nbsp;km.<ref name=“VI2029”/> This probability, combined with its size, caused Apophis to be assessed at level 4 on the [[Torino scale]]<ref name="nasanews146"/> and 1.10 on the [[Palermo scale]] (corresponding to an impact hazard over 12 times the background level), scales scientists use to represent how dangerous a given asteroid is to Earth. These are the highest values at which any object has been rated on either scale. The chance that there would be an impact in 2029 was eliminated later in the day of December 27, 2004, as a result of a [[precovery]] image that extended the observation arc back to March 2004.<ref name="nasanews148"/> The danger of a 2036 passage was lowered to level 0 on the Torino scale in August 2006.<ref name="Wayback2006-08"/> With a cumulative Palermo scale rating of −3.22,<ref name="riskneo"/> the risk of impact from Apophis is less than one thousandth the background hazard level.<ref name="riskneo"/>

In July 2005, former [[Apollo program|Apollo]] astronaut [[Rusty Schweickart]], as chairman of the [[B612 Foundation]], formally asked NASA to investigate the possibility that the asteroid's post-2029 orbit could be in [[orbital resonance]] with Earth, which would increase the probability of future impacts. Schweickart also asked NASA to investigate whether a [[transponder]] should be placed on the asteroid to enable more accurate tracking of how its orbit is affected by the [[Yarkovsky effect]].<ref name="Schweickart"/>

==== 2011 observations ====
On January 31, 2011, astronomers took the first new images of Apophis in more than 3 years.<ref name="Tholen"/>

[[File:Apophis ellipse.svg|thumb|right|Illustration of a common trend where progressively reduced uncertainty regions result in an asteroid impact probability increasing followed by a sharp decrease {{disputed|talkpage=Talk:Torino scale#Normal distribution|date=February 2025}}]]

==== 2013 refinement ====
The close approach in 2029 will substantially alter the object's orbit, prompting Jon Giorgini of JPL to say in 2011, "If we get radar ranging in 2013 [the next good opportunity], we should be able to predict the location of {{mp|2004 MN|4}} out to at least 2070."<ref name="Science"/> Apophis passed within {{convert|0.0966|AU|e6km e6mi|abbr=unit|lk=off}} of Earth in 2013, allowing astronomers to refine the trajectory for future close passes.<ref name=“esanews1”/><ref name=“NEODys”/><ref name="refine2013"/> Just after the closest approach on January 9, 2013,<ref name=“NEODys”/> the asteroid peaked at an [[apparent magnitude]] of about 15.6.<ref name="NEODyS2013"/> The [[Goldstone Deep Space Communications Complex|Goldstone]] radar observed Apophis during that approach from January 3 through January 17.<ref name="Goldstone"/> The [[Arecibo Observatory]] observed Apophis once it entered Arecibo's declination window after February 13, 2013.<ref name="Goldstone"/> The 2013 observations basically ruled out any chance of a 2036 impact.

A NASA assessment as of February 21, 2013, that did not use the January and February 2013 radar measurements gave an impact probability of 2.3 in a million for 2068.<ref name=“news178”/> As of May 6, 2013, using observations through April 15, 2013, the odds of an impact on April 12, 2068, as calculated by the JPL Sentry risk table had increased slightly to 3.9 in a million (1 in 256,000).<ref name="riskneo"/>

==== 2015 observations ====
As of January 2019, Apophis had not been observed since 2015, mostly because its orbit kept it very near the Sun from the perspective of Earth. It was not further than 60 degrees from the Sun between April 2014 and December 2019. With the early 2015 observations, the April 12, 2068, impact probability was 6.7 in a million (1 in 150,000), and the asteroid had a cumulative 9 in a million (1 in 110,000) chance of impacting Earth before 2106.<ref name="Sentry_Mar2015"/>

==== 2020–2021 observations ====
[[File:Apophis February 2021 NBO.webm|thumb|right|Apophis in February 2021]]

No observations of Apophis were made between January 2015 and February 2019 but observations began again in January 2020.<ref name="mpc"/> In March 2020, astronomers [[David Tholen]] and Davide Farnocchia measured the acceleration of Apophis due to the [[Yarkovsky effect]] for the first time, significantly improving the prediction of its orbit past the 2029 flyby. Tholen and Farnocchia found that the Yarkovsky effect causes the [[semi-major axis]] to decrease by about 170 metres per year, causing an increase in [[ecliptic longitude]] that is [[Quadratic function|quadratic]] in time.<ref name="TholenFarmocchia"/> In late 2020 Apophis approached the Earth and passed {{convert|0.11265|AU|e6km LD|abbr=unit}} from Earth on March 6, 2021, brightening to +15 [[apparent magnitude|mag]] at that time. Radar observations of Apophis were carried out at Goldstone in March 2021.<ref name=Jorge/><ref name="Goldstone2021"/> The asteroid has been observed by [[WISE spacecraft|NEOWISE]] (between December 2020 and April 2021)<ref name="Satpathy2022"/><ref name="FrankfurterRundschau_20210304"/> and by [[NEOSSat]] (in January 2021).<ref name="Reddy2022"/><ref name="IAWN2021"/><ref name="IAWN2021-Gallery"/>

These observations showed that a number called ζ (basically how far behind Earth Apophis would pass if it were not deflected by the gravitational pull of Earth) in 2029 will be about 47,363&nbsp;km,<ref name=Jorge>{{cite journal |last1=Jorge A. Pérez-Hernández & Luis Benet |title=Non-zero Yarkovsky acceleration for near-Earth asteroid (99942) Apophis |journal=Nature Communications Earth & Environment |date=January 11, 2022 |volume=3 |issue=1 |page=10 |doi=10.1038/s43247-021-00337-x |doi-access=free |bibcode=2022ComEE...3...10P }}</ref> less than the earlier nominal value of 47,659&nbsp;km by 296&nbsp;km because of the [[Yarkovsky effect]]. This means that Apophis will not hit the earth in the coming century, in particular avoiding the keyhole 212.14&nbsp;km below nominal that would have led to a collision in 2068.<ref name="Farnocchia2013_Icarus"/>

Apophis was the target of an observing campaign by the [[International Asteroid Warning Network]], resulting in the collection of [[light curves]], [[Astronomical spectroscopy|spectra]], and [[astrometry]].<ref name="Reddy2022"/><ref name="IAWN2021"/><ref name="IAWN2021-Gallery"/> The observations were used to practice and coordinate the response to an actual impact threat. Ignoring all earlier observations, the estimated probability of an impact in 2029 reached 16 percent before going down to zero.<ref name="PlanetaryDefense2021"/>

[[File:Apophis impact risk corridor 2029.jpg|thumb|left|upright=1.4|Hypothetical risk corridor for an impact on April 13, 2029, based on the 2020–21 planetary defense exercise]]

On February 21, 2021, Apophis was removed from the [[Sentry Risk Table]], as an impact in the next 100 years was finally ruled out.<ref name=“removed”>[https://cneos.jpl.nasa.gov/sentry/removed.html Removed Objects] from Sentry Risk Table</ref>

Several [[stellar occultation|occultations]] of bright stars ([[apparent magnitude]] 8–11) by Apophis occurred in March and April 2021.<ref name="JOA2021_3"/><ref name="Gaia_20210329"/><ref name="Tanga2021"/><ref name="Occultation award"/> A total of five separate occultations were observed successfully, marking the first time that an asteroid as small as Apophis was observed using the [[stellar occultation|occultation method]] (beating the previous record set in 2019 by asteroid [[3200 Phaethon]], which is more than ten times the size of Apophis).<ref name="Gaia_20210329"/> The first event, on March 7, was successfully observed from the United States by multiple observers.<ref name="SETI2021"/><ref name="Occultation_prelim"/><ref name="JOA2021_3"/> The next potential occultation, which occurred on March 11, was predicted to be visible from central Europe.<ref name="Tanga2021"/> This event was missed, mainly because of bad weather (two negative observations were recorded from [[Greece]]).<ref name="Gaia_20210329"/> On March 22, another occultation was observed only by a single observer from the United States, [[amateur astronomy|amateur astronomer]] Roger Venable. Larger-than-expected [[Errors and residuals|residuals]] in the March 7 data had caused the majority of observers to be deployed outside of the actual path for the March 22 occultation.<ref name="JOA2021_3"/> This single detection then allowed the prediction of several more events that would have been unobservable otherwise, including an occultation on April 4, which was observed from [[New Mexico]], again by Venable, alongside others.<ref name="Occultation award"/><ref name="JOA2021_3"/> Two more occultations, observable on April 10 and 11 from [[Japan]] and New Mexico, respectively, were seen by several observers each.<ref name="JOA2021_3"/>

On March 9, 2021, using radar observations from Goldstone taken on March 3–8 and three positive detections of the stellar occultation on March 7, 2021,<ref name="vvs.be"/> Apophis became the asteroid with the most precisely measured Yarkovsky effect of all asteroids, at a [[signal-to-noise ratio]] (SNR) of 186.4,<ref name="JPLdata_20210309"/>{{efn|name=Yarkovsky_20210309}} surpassing [[101955 Bennu]] (SNR=181.6).<ref name="YarkovskySNR"/>

The 2021 apparition was the last opportunity to observe Apophis before its 2029 flyby.<ref name="jpldata"/>
[[File:PIA24168-Asteroid-99942Apophis-RadarImages-20210326.jpg|thumb|center|upright=3|<div align="center">Asteroid 99942 Apophis – radar observations March 8–10, 2021 (March 26, 2021)</div>]]

=== History of impact estimates ===
{| class="wikitable sortable"
|-
! Date !! Time !! Status
|-
| rowspan=2 style="white-space: nowrap;" | 2004-12-23 ||style="white-space: nowrap;" | || The original NASA report mentioned impact chances of "around 1 in 300" in 2029, which was widely reported in the media.<ref name="nasanews146"/> The actual NASA estimates at the time were 1 in 233; these resulted in a Torino scale rating of 2, the first time any asteroid had received a rating above 1.
|-
| || Later that day, based on a total of 64 observations, the estimates were changed to 1 in 62 (1.6%), resulting in an update to the initial report and an upgrade to a Torino scale rating of 4.
|-
| 2004-12-25 || || The chances were first reported as 1 in 42 (2.4%) and later that day (based on 101 observations) as 1 in 45 (2.2%). At the same time, the asteroid's estimated diameter was lowered from 440&nbsp;m to 390&nbsp;m and its mass from 1.2×10<sup>11</sup>&nbsp;kg to 8.3×10<sup>10</sup>&nbsp;kg.
|-
| 2004-12-26|| || Based on a total of 169 observations, the impact probability was still estimated as 1 in 45 (2.2%), the estimates for diameter and mass were lowered to 380&nbsp;m and 7.5×10<sup>10</sup>&nbsp;kg, respectively.
|-
|rowspan=2 | 2004-12-27|| || Based on a total of 176 observations with an [[observation arc]] of 190 days, the impact probability was raised to 1 in 37 (2.7%)<ref name="mirror"/> with a line of variation (LOV) of only 83,000&nbsp;km;<ref name=“VI2029”>[https://web.archive.org/web/20050314032111/https://astro.uni-bonn.de/~dfischer/mirror/285neo041227.html Virtual Impactor for 2029-04-13] (Stretch LOV = 1.29E+1) * Earth radius of 6,420&nbsp;km = 82,818&nbsp;km.</ref> diameter was increased to 390&nbsp;m, and mass to 7.9×10<sup>10</sup>&nbsp;kg.
|-
| || Later that afternoon, a [[precovery]] increased the span of observations to 287 days, which eliminated the 2029 impact threat.<ref name="nasanews148"/> The cumulative impact probability was estimated to be around 0.004%, a risk lower than that of asteroid {{mpl|2004 VD|17}}, which once again became (temporarily) the greatest-risk object. A 2053 approach to Earth still posed a minor risk of impact, and Apophis was still rated at level one on the Torino scale for this orbit.
|-
| 2004-12-28 || style="white-space: nowrap;" | 12:23 GMT || Based on a total of 139 observations, a value of one was given on the Torino scale for 2044-04-13.29 and 2053-04-13.51.
|-
|rowspan=2 | 2004-12-29 || 01:10 GMT || The only pass rated 1 on the Torino scale was for 2053-04-13.51 based on 139 observations spanning 287.71 days (2004-Mar-15.1104 to 2004-Dec-27.8243).
|-
| 19:18 GMT || This was still the case based upon 147 observations spanning 288.92&nbsp;days (2004-Mar-15.1104 to 2004-Dec-29.02821), though the close encounters were changed and reduced to 4 in total.
|-
|rowspan=2 | 2004-12-30 || 13:46 GMT || No passes were rated above 0, based upon 157&nbsp;observations spanning 289.33&nbsp;days (2004-Mar-15.1104 to 2004-Dec-29.44434). The most dangerous pass was rated at 1 in 7,143,000.
|-
| 22:34 GMT || 157 observations spanning 289.33 days (2004-Mar-15.1104 to 2004-Dec-29.44434). One pass at 1 (Torino scale) 3 other passes.
|-
| 2005-01-02 || 03:57 GMT || Observations spanning 290.97 days (2004-Mar-15.1104 to 2004-Dec-31.07992) One pass at 1 (Torino scale) 19 other passes.
|-
| 2005-01-03 || 14:49 GMT || Observations spanning 292.72 days (2004-Mar-15.1104 to 2005-Jan-01.82787) One pass at 1 (Torino scale) 15 other passes.
|-
| 2005–01 || || Extremely precise [[radar]] observations at [[Arecibo Observatory]]<ref name=“Arecibo”/> refine the orbit further and show that the April 2029 close approach will occur at only 5.7&nbsp;[[Earth radii]],<ref name="nasanews149"/> approximately one-half the distance previously estimated.
|-
| 2005-02-06 || || Apophis estimated to have a 1-in-13,000 chance of impacting in April 2036.<ref name="Wayback2005-02"/>
|-
| 2005-08-07 || ||Radar observation<ref name=“Arecibo”/> refines the orbit further and eliminates the possibility of an impact in 2035. Only the pass in 2036 remains at Torino scale&nbsp;1 (with a 1-in-5,560 chance of impact).<ref name="Wayback2005-10"/>
|-
| 2005–10 || || It is predicted that Apophis will pass just below the altitude of [[geosynchronous satellite]]s, which are at approximately {{convert|35900|km|mi}}.<ref name="Wee2012"/> Such a close approach by an asteroid of that size is estimated to occur every 800 years or so.<ref name="neo"/>
|-
| 2006-05-06 || || Radar observation at Arecibo Observatory<ref name=“Arecibo”/> slightly lowered the Palermo scale rating, but the pass in 2036 remained at Torino scale&nbsp;1<ref name="Wayback2006-07"/> despite the impact probability dropping by a factor of four.
|-
| 2006-08-05 || || Additional observations through 2006 resulted in Apophis being lowered to Torino scale&nbsp;0.<ref name="Wayback2006-08"/> (The impact probability was assessed as 1 in 45,000.)<ref name="Wayback2006-08"/>
|-
| 2008-04 || || News outlets carry the story that 13-year-old German student [[Nico Marquardt]] found a probability of 1 in 450 for a 2036 impact.<ref name="Bild.de"/><!--Here are the references from the Wikipedia article on Marquardt, in case that article gets deleted:ref>{{cite web|title=Ragazzino calcola la fine del mondo|url=http://www.corriere.it/scienze/08_aprile_17/fine_mondo_calcolo_ragazzino_nasa_11d11136-0c45-11dd-aecb-00144f486ba6.shtml|publisher=[[Corriere della Sera]]|date=April 17, 2008|access-date=November 8, 2015}}</ref><ref>{{cite web|title=Niño alemán corrige cálculos a la NASA|url=http://www.cnnexpansion.com/economia-insolita/nino-aleman-corrige-calculos-a-la-nasa#|publisher=[[CNN]]|date=April 16, 2008|access-date=November 8, 2015}}</ref><ref>{{cite web|title=13-year-old corrects NASA's asteroid figures|url=http://www.chinadaily.com.cn/world/2008-04/16/content_6620949.htm|publisher=[[China Daily]]|date=April 16, 2008|access-date=November 8, 2015}}</ref><ref>{{cite web|title=Un petit génie allemand met la NASA en échec|url=http://www.rtl.fr/actu/societe-faits-divers/un-petit-genie-allemand-met-la-nasa-en-echec-86494|publisher=[[RTL (French radio)]]|date=April 16, 2008|access-date=November 8, 2015}}</ref><ref>{{cite web|title=NASA says German whiz-kid got it wrong|url=http://www.abc.net.au/science/articles/2008/04/17/2219493.htm?site=science/footprintsonthemoon&topic=latest|publisher=[[Australian Broadcasting Corporation|ABC]]|date=April 17, 2008|access-date=November 8, 2015}}</ref><ref>{{cite web|title=Schoolboy corrects NASA 'killer asteroid' maths'|url=http://www.theage.com.au/news/world/schoolboy-corrects-nasa-killer-asteroid-maths/2008/04/16/1208025230056.html|publisher=[[The Age]]|date=April 16, 2008|access-date=November 8, 2015}}</ref>--> This estimate was allegedly acknowledged by [[ESA]] and NASA<ref name="RadioCanada"/><ref name="Schoolboy"/><ref name="Bild.de"/> but in an official statement,<ref name="NASAkid"/> NASA denied they had made an error. The release went on to explain that since the angle of Apophis's approach to the Earth's equator means the asteroid will not travel through the belt of current [[equatorial orbit|equatorial]] geosynchronous satellites, there is currently no risk of collision; and the effect on Apophis's orbit of any such impact would be insignificant.
|-
| 2009-04-29 || || An animation is released<ref name="ApophisBias"/> that shows how unmeasured physical parameters of Apophis bias the entire statistical uncertainty region. If Apophis is a [[retrograde motion|''retrograde'' rotator]] on the small, less-massive end of what is possible, it will be several hundred kilometres further ahead in 2029, resulting in a different change to its orbit, and then the measurement uncertainty region for 2036 will get pushed back such that the center of the distribution encounters Earth's orbit. This would result in an impact probability much higher than computed with the Standard Dynamical Model. Conversely, if Apophis is a small, less-massive ''prograde'' rotator, it arrives a bit later on April 13, 2029, and the uncertainty region for 2036 is advanced along the orbit. Only the remote tails of the probability distribution could encounter Earth, producing a negligible impact probability for 2036.<ref name="neo"/><ref name=“Predicting”/>
|-
| 2009-10-07 || || Refinements to the [[precovery]] images of Apophis by the University of Hawaii's [[Institute for Astronomy (Hawaii)|Institute for Astronomy]], the 90-inch [[Bok Telescope]], and the [[Arecibo Observatory]] have generated a refined path that reduces the odds of an April 13, 2036, impact to about 1 in 250,000.<ref name=“Brown2009”/>
|-
| || || Criticism of older published impact probabilities rests on the fact that important physical parameters such as mass and spin that affect its precise trajectory had not yet been accurately measured and hence there were no associated probability distributions. The Standard Dynamical Model used for making predictions simplifies calculations by assuming Earth is a point mass. This could lead to a prediction error of up to 2.9 Earth radii for the 2036 approach, necessitating the consideration of Earth's oblateness during the 2029 passage for accurately forecasting the potential impact.<ref name="neo"/> Additional factors that could greatly influence the predicted motion in ways that depend on unknown details, were the spin of the asteroid,<ref name="TrajectoryChange"/> its precise mass, the way it reflects and absorbs sunlight, radiates heat, and the gravitational pull of other asteroids passing nearby.<ref name="neo"/> Small uncertainties in the masses and positions of the [[planet]]s and [[Sun]] could cause up to 23 Earth radii of prediction error for Apophis by 2036.<ref name="neo"/>
|-
| 2013-01 || || A statistical impact risk analysis of the data up to this point calculated that the odds of the 2036 impact at 7.07 in a billion, effectively ruling it out. The same study looked at the odds of an impact in 2068, which were calculated at 2.27 in a million.<ref name="Farnocchia2013_Icarus"/> First appearance of Sentry virtual impactors that also include mid-October dates.<ref name="Wayback2013-01"/>
|-
| 2013-01-09 || || The [[European Space Agency]] (ESA) announced that the [[Herschel Space Observatory]] made new thermal infrared observations of the asteroid as it approached Earth. The initial data shows the asteroid to be bigger than first estimated because it is now expected to be less reflective than originally thought.<ref name=“esanews1”/> The Herschel Space Observatory observations increased the diameter estimate by 20% from 270 to 325 metres, which translates into a 75% increase in the estimates of the asteroid's volume or mass.<ref name=“esanews1”/> Goldstone single-pixel observations of Apophis have ruled out the potential 2036 Earth impact.<ref name="NASA2013-017"/><ref name="Beatty2013"/><ref name="Plait2013"/> Apophis will then come no closer than about {{convert|14|e6mi|e6km|order=flip}}—and more likely miss us by something closer to {{convert|35|e6mi|e6km|order=flip}}.<ref name="Beatty2013"/> The radar astrometry is more precise than was expected.<ref name="Beatty2013"/>
|-
| 2014-10-8 || || The [[Sentry Risk Table]] assessed Apophis as having a 6.7-in-a-million (1-in-150,000) chance of impacting Earth in 2068, and a 9-in-a-million (1-in-110,000) cumulative chance of impacting Earth by 2105.<ref>{{cite web|title=99942 Apophis (2004 MN4) Earth Impact Risk Summary|publisher=NASA/JPL|date=October 8, 2014|url=http://neo.jpl.nasa.gov/risk/a99942.html|archive-url=https://web.archive.org/web/20160323214134/http://neo.jpl.nasa.gov/risk/a99942.html|archive-date=March 23, 2016|url-status=dead}}</ref>
|-
| 2020-03 || || By taking observations of Apophis with the [[Subaru Telescope]] in January and March 2020, as well as remeasuring older observations using the new [[Gaia DR2]] star catalog, astronomers positively detect the [[Yarkovsky effect]] on Apophis. The [[semi-major axis]] thereby decreases by about 170 metres per year. The Yarkovsky effect is the main source of uncertainty in impact probability estimates for this asteroid.<ref name="TholenFarmocchia"/>
|-
| 2021-02-21 || || Apophis was removed from the [[Sentry Risk Table]], as an impact in the next 100 years was finally ruled out.<ref name=“removed”/>
|-
| 2021-03-15 || 10:44 || JPL solution #207 using observations in 2020 and 2021 reduced the 3-sigma uncertainty region in the 2029 approach distance from ±700&nbsp;km<ref name=“JPLSBDB2020”>{{Cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=99942;cad=1|title=JPL Small-Body Database Browser|date=November 6, 2020|archive-url=https://web.archive.org/web/20201106120010/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=99942;cad=1|archive-date=November 6, 2020}}</ref> to about ±3&nbsp;km.<ref name="jpldata"/> The June 2021 solution showed the Earth approach on March 27, 2036, will be no closer than {{convert|0.30889|AU|e6km e6mi LD|abbr=unit|lk=in}}.<ref name="jpldata"/>
|-
| 2024-06-25 || || JPL solution #220 includes observations through 2022-April-09.<ref name="jpldata"/>
|}

== Possible impact effects ==
As of 2021, the Sentry Risk Table estimated that Apophis would impact Earth with [[kinetic energy]] equivalent to 1,200 MT or [[TNT equivalent|megatons of TNT]].<ref name="riskneo"/> In comparison, the energy released by the eruption of Krakatoa was 200 MT, total global nuclear arsenal has an energy equivalent to 1,460 MT, and the [[Chicxulub crater|Chicxulub impact and extinction event]] had an estimated energy of 100,000,000 MT (100 teratons). See [[TNT_equivalent#Examples|TNT equivalent examples]] for an extended table of comparable energies.

The exact effects of an impact would vary based on the asteroid's composition, and the location and angle of impact. Any impact of Apophis would be extremely detrimental to an area of thousands of square kilometres, but would be unlikely to have long-lasting global effects, such as the initiation of an [[impact winter]].<ref>{{Cite journal|last1=Baurov|first1=Y.A.|last2=Albanese|first2=L.|last3=Meneguzzo|first3=F.|last4=Menshikov|first4=V.A.|title=Protecting the planet from the asteroid hazard|url=https://www.researchgate.net/publication/260818491|year=2013|volume=9|issue=3|journal=Int. J. Pure Appl. Phys. |pages=151–168}}</ref> Assuming Apophis is a {{convert|370|m|ft|adj=mid|-wide}} stony asteroid with a density of 3,000&nbsp;kg/m<sup>3</sup>, if it were to impact into [[sedimentary rock]], Apophis would create a {{convert|5.1|km|ft|adj=mid}} [[impact crater]].<ref name="Earth-impact"/><ref name="riskneo"/>
===Expired 2036 path of risk===
In 2008, the [[B612 Foundation]] made estimates of Apophis's path if a 2036 Earth impact were to occur, as part of an effort to develop viable [[Asteroid deflection strategies|deflection strategies]].<ref name="Schweickart2"/> The result was a narrow corridor a few kilometres wide, called the "path of risk", extending across southern [[Russia]], across the north [[Pacific]] (relatively close to the coastlines of [[California]] and [[Mexico]]), then right between [[Nicaragua]] and [[Costa Rica]], crossing northern [[Colombia]] and [[Venezuela]], ending in the [[Atlantic]], just before reaching [[Africa]].<ref>''Range of Possible Impact Points on April 13, 2036'' in [http://www.aero.org/conferences/planetarydefense/2007papers/S3-4--Gennery-Brief.pdf Scenarios for Dealing with Apophis], by Donald B. Gennery, presented at the Planetary Defense Conference. Washington, DC. March 5–8, 2007 (archived from [https://web.archive.org/web/20120412123940/http://www.aero.org/conferences/planetarydefense/2007papers/S3-4--Gennery-Brief.pdf the original] on April 12, 2012).</ref> Using the computer simulation tool NEOSim, it was estimated that the hypothetical impact of Apophis in countries such as Colombia and Venezuela, which were in the path of risk, could have more than 10 million casualties.<ref name="Baileya2006"/> A deep-water impact in the Atlantic or Pacific oceans would produce an incoherent short-range [[tsunami]] with a potential destructive radius (inundation height of >2&nbsp;m) of roughly {{convert|1000|km}} for most of North America, Brazil and Africa, {{convert|3000|km|abbr=on}} for Japan and {{convert|4500|km|abbr=on}} for some areas in Hawaii.<ref name="Paine1999"/>

== Exploration ==

=== OSIRIS-APEX post-Earth-encounter rendezvous ===
The ''[[OSIRIS-REx]]'' spacecraft returned a sample of [[Bennu (asteroid)|Bennu]] to Earth on September 24, 2023.<ref>{{cite report|title=OSIRIS-REx factsheet|date=August 2011|publisher=[[NASA]]|department=Explorers and Heliophysics Projects Division|place=[[Goddard Space Flight Center|Goddard SFC]]|website=ehpd.gsfc.nasa.gov|url=https://ehpd.gsfc.nasa.gov/documents/552572main_OSIRIS_REx_Factsheet.pdf}} {{PD-notice}}</ref> After ejecting the sample canister, the spacecraft can use its remaining fuel to target another body during an extended mission. Apophis is the only asteroid which the spacecraft could reach for a long-duration rendezvous, rather than a brief [[planetary flyby|flyby]]. In April 2022, the extension was approved, and ''OSIRIS-REx'' will perform a rendezvous with Apophis in April 2029, a few days after the close approach to Earth. It will study the asteroid for 18 months and perform a maneuver similar to the one it made during sample collection at Bennu, by approaching the surface and firing its thrusters. This will expose the asteroid's subsurface and allow mission scientists to learn more about the asteroid's material properties.<ref name="Bartels2021"/><ref name="Lauretta2020"/> For its Apophis mission after the sample return, ''OSIRIS-REx'' was renamed ''OSIRIS-APEX'' (short for OSIRIS-Apophis Explorer).<ref>{{Cite web|date=April 25, 2022|title=NASA gives green light for OSIRIS-REx spacecraft to visit another asteroid|url=https://news.arizona.edu/story/nasa-gives-green-light-osiris-rex-spacecraft-visit-another-asteroid|access-date=April 26, 2022|publisher=University of Arizona News|first=Mikayla|last=Mace Kelley}}</ref>

=== Other proposed space missions ===
==== Planetary Society competition ====
In 2007, the [[Planetary Society]], a [[California]]-based space advocacy group, organised a $50,000 competition to design an uncrewed space probe that would 'shadow' Apophis for almost a year, taking measurements that would "determine whether it will impact Earth, thus helping governments decide whether to mount a deflection mission to alter its orbit". The society received 37&nbsp;entries from 20&nbsp;countries on 6&nbsp;continents.<ref name="Planetary2007">{{Cite web|url=https://www.planetary.org/press-releases/0226_planetary_society_names_winners_of|title=Planetary Society Names Winners of $50,000 Asteroid Tagging Competition|last=Kaplan|first=Mat|date=February 26, 2008|website=www.planetary.org|archive-url=https://web.archive.org/web/20200812145258/https://www.planetary.org/press-releases/0226_planetary_society_names_winners_of|archive-date=August 12, 2020|url-status=live}}</ref>

The commercial competition was won by a design called ''Foresight'' created by [[SpaceWorks Engineering]].<ref name="competition"/><ref name="Planetary2007"/>{{clarify|date=November 2024|reason=An earlier version of this article stated that the competition was won by SpaceWorks Enterprises, but both sources disagree. Is this a different name for the same company?}} SpaceWorks proposed a simple orbiter with only two instruments and a radio beacon at a cost of ~US$140&nbsp;million, launched aboard a [[Minotaur (rocket family)|Minotaur IV]] between 2012 and 2014. ''Pharos'', the winning student entry, would be an orbiter with four science instruments that would rendezvous with and track Apophis. The spacecraft would have been launched in April or May 2013 aboard a [[Delta II 7925]] rocket, to arrive at the asteroid after a cruise of 233 to 309 days. It would have carried four additional ''BUOI'' probes that would have impacted the surface of Apophis over the course of two weeks.<ref name="Planetary2007"/><ref>{{Cite web|url=https://ntrs.nasa.gov/api/citations/20120000562/downloads/20120000562.pdf|title=PHAROS: Shedding Light on the Near-Earth Asteroid Apophis|work=ESMD Space Grant Systems Engineering Paper Competition|date=April 30, 2007|publisher=Georgia Institute of Technology|first1=Jonathan|last1=Sharma|first2=Jarret|last2=Lafleur|first3=Nilesh|last3=Shah|first4=Jilian|last4=Apa|first5=Jonathan|last5=Townley|first6=Kreston|last6=Barron|archive-url=https://web.archive.org/web/20241115143132/https://ntrs.nasa.gov/api/citations/20120000562/downloads/20120000562.pdf|archive-date=November 15, 2024|url-status=live}}</ref>

==== Don Quijote mission ====
Apophis is one of two asteroids that were considered by the [[European Space Agency]] as the target of its [[Don Quijote (spacecraft)|Don Quijote mission concept]] to study the effects of impacting an asteroid.<ref name="DonQuixote"/>

==== Chinese mission ====
China had planned an encounter with Apophis in 2022, several years prior to the close approach in 2029. This mission, now known as ''[[Tianwen-2]]'', would have included exploration and close study of three asteroids including an extended encounter with Apophis for close observation, and land on the asteroid [[(175706) 1996 FG3|1996 FG<sub>3</sub>]] to conduct in situ sampling analysis on the surface.<ref name="XinhuaNews"/> The launch date is now scheduled for May 2025, with a different set of targets.<ref name="sn-20230626">{{cite web|last=Jones|first=Andrew|url=https://spacenews.com/china-conducts-parachute-tests-for-asteroid-sample-return-mission/|title=China conducts parachute tests for asteroid sample return mission|work=[[SpaceNews]]|date=June 26, 2023|access-date=October 28, 2024}}</ref>

==== RAMSES ====
Apophis is the target of the [[European Space Agency]]'s proposed [[Ramses (spacecraft)|RAMSES]] (Rapid Apophis Mission for Security and Safety) mission, with a launch in April 2028 and rendezvous with the asteroid in 2029.<ref name=“RAMSES”>{{cite arXiv|last1=Morelli|first1=Andrea C.|last2=Mannocchi|first2=Alessandra|display-authors=etal|date=September 2023|title=Initial Trajectory Assessment of the RAMSES Mission to (99942) Apophis|eprint=2309.00435|class=astro-ph.EP}}</ref><ref>{{cite web|last1=Bartels|first1=Meghan|title=Europe Announces New Mission to Infamous Asteroid Apophis|url=https://www.scientificamerican.com/article/asteroid-apophis-is-target-of-europes-new-ramses-mission/|work=[[Scientific American]]|access-date=October 28, 2024}}</ref>{{clarify|date=October 2024|reason=Mannocchi et al. give possible launch dates of November–December 2026, April–May 2027, September–November 2027, or March–May 2028, with a launch in 2027 being the preferred option. The Scientific American article simply states that the latest launch opportunity is around April 2028, which does not imply that a launch in 2028 is expected.}}

== Proposed deflection strategies ==
{{further|Asteroid impact avoidance}}
Studies by NASA, ESA,<ref name="Izzo2006"/> and various research groups in addition to the Planetary Society contest teams,<ref name="aero.org"/> have described a number of proposals for deflecting Apophis or similar objects, including [[gravitational tractor]], [[Asteroid deflection strategies|kinetic impact]], and [[nuclear bomb]] methods.

On December 30, 2009, [[Anatoly Perminov]], the director of the Russian Federal Space Agency, said in an interview that [[Roscosmos]] will also study designs for a possible deflection mission to Apophis.<ref name="Isachenkov2009"/>

On August 16, 2011, researchers at China's [[Tsinghua University]] proposed launching a mission to knock Apophis onto a safer course using an impactor spacecraft in a retrograde orbit, steered and powered by a solar sail. Instead of moving the asteroid on its potential resonant return to Earth, Shengping Gong and his team believe the secret is shifting the asteroid away from entering the gravitational keyhole in the first place.<ref name="ChinaSail"/>

On February 15, 2016, Sabit Saitgarayev, of the [[Makeyev Rocket Design Bureau]], announced intentions to use [[Russia]]n [[ICBM]]s to target relatively small [[near-Earth object]]s. Although the report stated that likely targets would be between the 20 to 50 metres in size, it was also stated that 99942 Apophis would be an object subject to tests by the program.<ref name="TASS"/>

In October 2022, a method of mapping the inside of a potentially problematic asteroid, such as 99942 Apophis, in order to determine the best area for impact was proposed.<ref name="WP-20221021">{{cite news|last=Verma|first=Pranshu|title=There's a new tool to help blow up asteroids – Researchers from MIT and Stanford have created a tool that could improve the aim of future planetary defense missions|url=https://www.washingtonpost.com/technology/2022/10/21/asteroid-destruction-tool/|date=October 21, 2022|newspaper=The Washington Post|access-date=October 22, 2022}}</ref>

== Popular culture ==
In [[Id Software]]'s [[video game]] ''[[Rage (video game)|Rage]]'', the backstory involves the asteroid colliding with Earth on August 23, 2029. The asteroid almost wipes out the human race and ushers in a [[post-apocalyptic]] age.<ref name="Gamespot" />
<!-- Make sure that anything you add is properly referenced with reliable sources. Unsourced material will be removed. -->

== See also ==
{{div col|colwidth=20em}}
* [[Asteroid capture]]
* [[Asteroid impact prediction]]
* [[Asteroid Redirect Mission]]
* [[Earth-grazing fireball]]
* [[List of impact craters on Earth]]
* [[NEO Surveyor]]
{{div col end}}

== Notes ==
{{notelist|refs=

{{efn|name=palermo|Of the six asteroids with a higher Palermo scale rating than Apophis at the time:
* [[(29075) 1950 DA]] and [[101955 Bennu]] cannot impact within the next 100 years;
* [[1979 XB]] and [[2007 FT3]] are lost [[Observation arc#Short arcs|short-arc]] objects that cannot be recovered with targeted observations and await serendipitous [[astronomical survey|survey]] observations;
* [[2000 SG344]] and 2009 JF1 are less than 50 metres in diameter.}}

{{efn|name=Yarkovsky_20210309|Using the March 9, 2021, solution, JPL gave the strength of the Yarkovsky effect as <math>A_{2}=-2.877\times10^{-14}\text{ AU/d}^{2}</math>, with an uncertainty of <math>1.543\times10^{-16}\text{ AU/d}^{2}</math>. The SNR, defined as the size of the signal divided by the uncertainty, is <math>2.877\times10^{-14}/1.543\times10^{-16}=186.4</math>. As of the latest orbit solution (June 29, 2021), the SNR is <math>2.901\times10^{-14}/1.942\times10^{-16}=149.4</math> (again lower than Bennu's).}}

{{efn|name=Venus2022|On [[List of asteroid close approaches to Earth in 2022#Venus|January 8, 2022]] Venus was even closer to Earth at {{convert|0.2658|AU|e6km e6mi LD|abbr=unit|lk=off}}.}}

}} <!-- end of notelist -->

== References ==
{{reflist|refs =

<ref name="jpldata">{{cite web|type=last observation: April 09, 2022; [[Observation arc|arc]]: 18.07 years; JPL #220 solution date: 2024-Jun-25|title=JPL Small-Body Database Browser: 99942 Apophis (2004 MN4)|url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Apophis&view=OPC|access-date=February 28, 2025}}</ref>

<ref name=“NEODys”>{{cite web|title=NEODyS : (99942) Apophis (Close Approaches)|publisher=NEODyS (Near Earth Objects—Dynamic Site)|url=https://newton.spacedys.com/neodys/index.php?pc=1.1.8&n=99942|access-date=March 14, 2021}}</ref>

<ref name="mpc">{{cite web|title=(99942) Apophis Orbit|publisher=IAU Minor Planet Center|url=http://www.minorplanetcenter.net/db_search/show_object?object_id=99942|access-date=April 1, 2021}}</ref>

<ref name=“esanews1”>{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/Herschel_intercepts_asteroid_Apophis|title=Herschel intercepts asteroid Apophis|author=ESA|publisher=[[European Space Agency]] (ESA)|date=January 9, 2013|access-date=January 9, 2013}}</ref>

<ref name="Goldstone">{{cite web|title=99942 Apophis 2013 Goldstone Radar Observations Planning|publisher=NASA/JPL Asteroid Radar Research|last=Benner|first=L. A. M.|url=http://echo.jpl.nasa.gov/asteroids/Apophis/Apophis_2013_planning.html|date=January 9, 2013|access-date=January 9, 2013}}</ref>

<ref name="Beatty2013">{{cite web|date=January 9, 2013|title=Asteroid Apophis Takes a Pass in 2036|publisher=[[Sky & Telescope]]|author=Kelly Beatty|url=http://www.skyandtelescope.com/astronomy-news/asteroid-apophis-takes-a-pass-in-2036/|access-date=November 10, 2014}}</ref>

<ref name="Brozovic2018">{{cite journal|url=https://echo.jpl.nasa.gov/asteroids/brozovic.etal.apophis.2018.pdf|title=Goldstone and Arecibo radar observations of (99942) Apophis in 2012–2013|first1=M.|last1=Brozović|first2=L. A. M.|last2=Benner|first3=J. G.|last3=McMichael|first4=J. D.|last4=Giorgini|first5=P.|last5=Pravec|first6=P.|last6=Scheirich|first7=C.|last7=Magric|first8=M. W.|last8=Busch|first9=J. S.|last9=Jao |first10=C. G. |last10=Lee|first11=L. G.|last11=Snedeker|first12=M. A.|last12=Silva|first13=M. A.|last13=Slade|first14=B.|last14=Semenov|first15=M. C.|last15=Nolan|first16=P. A.|last16=Taylor|first17=E. S.|last17=Howell|first18=K. J.|last18=Lawrence|display-authors=4|journal=Icarus|volume=300|date=January 15, 2018|pages=115–128|access-date=August 19, 2018|bibcode=2018Icar..300..115B|doi=10.1016/j.icarus.2017.08.032}}</ref>

<ref name="NASA2013-017">{{cite web|title=NASA Rules Out Earth Impact in 2036 for Asteroid Apophis|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.php?release=2013-017|date=January 10, 2013|access-date=January 10, 2013}}</ref>

<ref name="Plait2013">{{cite journal|title=Impact Threat from Near-Earth Asteroid Apophis in 2036 Now Ruled Out|publisher=Bad Astronomy blog|author=Phil Plait|journal=Slate|author-link=Phil Plait|url=http://www.slate.com/blogs/bad_astronomy/2013/01/10/apophis_impact_new_observation_show_it_to_be_bigger_but_no_longer_a_threat.html|date=January 10, 2013|access-date=January 10, 2013}}</ref>

<ref name="phys">{{cite web|title=99942 Apophis|publisher=The Near-Earth Asteroids Data Base at E.A.R.N|url=http://earn.dlr.de/nea/099942.htm|access-date=October 15, 2009|archive-url=https://web.archive.org/web/20120616092526/http://earn.dlr.de/nea/099942.htm|archive-date=June 16, 2012|url-status=dead}}</ref>

<ref name=“tumblingspinstate”>{{cite journal|title=The tumbling spin state of (99942) Apophis|last1=Pravec|first1=P.|last2=Scheirich|first2=P.|last3=Ďurech|first3=J.|last4=Pollock|first4=J.|last5=Kušnirák|first5=P.|last6=Hornoch|first6=K.|last7=Galád|first7=A.|last8=Vokrouhlický|first8=D.|last9=Harris|first9=A.W. |last10=Jehin |first10=E.|last11=Manfroid|first11=J.|last12=Opitom|first12=C.|last13=Gillon|first13=M.|last14=Colas|first14=F.|last15=Oey|first15=J.|last16=Vraštil|first16=J.|last17=Reichart|first17=D.|last18=Ivarsen|first18=K.|last19=Haislip|first19=J. |last20=LaCluyze |first20=A.|display-authors=4|journal=Icarus|date=2014|url=http://sajri.astronomy.cz/pravecetal2014.pdf|volume=233|pages=48–60|doi=10.1016/j.icarus.2014.01.026|bibcode=2014Icar..233...48P|access-date=November 26, 2014|archive-date=March 5, 2016|archive-url=https://web.archive.org/web/20160305030401/http://sajri.astronomy.cz/pravecetal2014.pdf|url-status=dead}}</ref>

<ref name=“keyhole”>{{cite magazine|title=5 Plans to Head Off the Apophis Killer Asteroid|url=https://www.popularmechanics.com/space/deep-space/a1025/4201569/|archive-url=https://web.archive.org/web/20180612211352/https://www.popularmechanics.com/space/deep-space/a1025/4201569/|url-status=live|archive-date=June 12, 2018|magazine=[[Popular Mechanics]]|date=November 7, 2006|author=David Noland|access-date=March 14, 2021}}</ref>

<ref name="nasanews146">{{cite news|url=http://cneos.jpl.nasa.gov/news/news146.html|title=Near-Earth Asteroid 2004 MN4 Reaches Highest Score To Date On Hazard Scale|first1=D.|last1=Yeomans|first2=S.|last2=Chesley|first3=P.|last3=Chodas|publisher=[[NASA]]/[[Jet Propulsion Laboratory|JPL]] [[Center for Near-Earth Object Studies|CNEOS]]|date=December 23, 2004|access-date=January 31, 2024|quote=Today's impact monitoring results indicate that the impact probability for April 13, 2029, has risen to about 1.6%, which for an object of this size corresponds to a rating of 4 on the ten-point Torino Scale.}}</ref>

<ref name="nasanews148">{{cite news|title=Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4|publisher=NASA/JPL CNEOS|first1=D.|last1=Yeomans|first2=P.|last2=Chodas|first3=S.|last3=Chesley|url=http://cneos.jpl.nasa.gov/news/news148.html|date=December 27, 2004|access-date=January 31, 2024}}</ref>

<ref name="nasanews149">{{cite news|title=Radar Observations Refine the Future Motion of Asteroid 2004 MN4|publisher=NASA's Near Earth Object Program Office|first1=P.|last1=Chodas|first2=S.|last2=Chesley|first3=J.|last3=Giorgini|first4=D.|last4=Yeomans|url=http://cneos.jpl.nasa.gov/news/news149.html|date=February 3, 2005|access-date=January 31, 2024}}</ref>

<ref name="nasanews164">{{cite news|title=NASA Refines Asteroid Apophis' Path Toward Earth|publisher=NASA's Near Earth Object Program Office|first1=D.|last1=Brown|url=http://cneos.jpl.nasa.gov/news/news164.html|date=October 7, 2009|access-date=January 31, 2024}}</ref>

<ref name="risk-table">{{cite web|title=Sentry: Earth Impact Monitoring|publisher=NASA/JPL Center for NEO Studies|url=https://cneos.jpl.nasa.gov/sentry/|archive-url=https://web.archive.org/web/20210324054532/https://cneos.jpl.nasa.gov/sentry/|archive-date=March 24, 2021|url-status=dead|access-date=March 3, 2021}} (Use Unconstrained Settings to reveal 1979 XB with impact probability below 1e-6)</ref>

<ref name="riskneo">{{cite web|title=99942 Apophis (2004 MN4) Earth Impact Risk Summary|publisher=[[NASA]]/JPL Center for NEO Studies|url=http://neo.jpl.nasa.gov/risk/a99942.html|archive-url=https://web.archive.org/web/20130511010048/http://neo.jpl.nasa.gov/risk/a99942.html|archive-date=May 11, 2013|date=May 6, 2013|url-status=dead}} See also updated version at {{cite web|title=Sentry: Earth Impact Monitoring, Object Details|publisher=NASA/JPL Center for NEO Studies|access-date=February 8, 2021|archive-url=https://web.archive.org/web/20210208132353/https://cneos.jpl.nasa.gov/sentry/details.html#?des=99942|url=https://cneos.jpl.nasa.gov/sentry/details.html#?des=99942|archive-date=February 8, 2021|url-status=dead}}</ref>

<ref name="Earth-impact">{{cite web|title=Earth Impact Effects Program|publisher=Imperial College London / Purdue University|first1=R.|last1=Marcus|first2=H. J.|last2=Melosh|first3=G.|last3=Collins|url=http://impact.ese.ic.ac.uk/ImpactEffects/|date=2010|access-date=March 14, 2021}} (solution using 370 metres, 3000&nbsp;kg/m<sup>3</sup>, 12.6&nbsp;km/s, 45 degrees)</ref>

<ref name=“Reddy2018”>{{cite journal|last1=Reddy|first1=V.|last2=Sanchez|first2=J. A.|last3=Furfaro|first3=R.|last4=Binzel|first4=R. P.|last5=Burbine|first5=T. H.|last6=Le Corre|first6=L.|last7=Hardersen|first7=P. S.|last8=Bottke|first8=W. F.|last9=Brozovic|first9=M.|display-authors=4|title=Surface Composition of (99942) Apophis|journal=The Astronomical Journal|publisher=American Astronomical Society|volume=155|issue=3|date=March 5, 2018|issn=1538-3881|doi=10.3847/1538-3881/aaaa1c|page=140|arxiv=1803.05375|bibcode=2018AJ....155..140R|s2cid=78087061|doi-access=free}}</ref>

<ref name="Orbit2029">{{cite web|title=Horizons Batch for Apophis Orbital Elements for 2029-01-01 and 2030-01-01|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%272029-01-01%27&STOP_TIME=%272030-01-01%27&STEP_SIZE=%271%20year%27&CENTER=%27@Sun%27&OUT_UNITS=%27AU-D%27|access-date=July 31, 2022}}</ref>

<ref name="Horizons2029">{{cite web|title=Horizons Batch for Apophis @ 2029-Apr-13 21:45:03.5 showing 3-sigma uncertainty of ±3.3km|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272029-Apr-13%2021:45:03%27&STOP_TIME=%272029-Apr-13%2021:45:04%27&STEP_SIZE=%272%27&QUANTITIES=%2720,39%27|archive-url=https://web.archive.org/web/20220131021056/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272029-Apr-13%2021:46%27&STOP_TIME=%272029-Apr-14%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27|archive-date=January 31, 2022|url-status=live|access-date=February 28, 2025}}</ref>

<ref name="Horizons2036">{{cite web|title=Horizons Batch for Apophis @ 2036-Mar-27 08:31 showing 3-sigma uncertainty of ±124566km|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272036-Mar-27%2008:31%27&STOP_TIME=%272036-Mar-28%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27|archive-url=https://web.archive.org/web/20230710121335/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272036-Mar-27%2008:30%27&STOP_TIME=%272036-Mar-28%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27|archive-date=July 10, 2023|url-status=live|access-date=February 28, 2025}}</ref>

<ref name="Horizons2116">{{cite web|title=Horizons Batch for Apophis @ 2116-Apr-12 21:44 showing 3-sigma uncertainty of ±13 million km|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272116-Apr-12%2021:44%27&STOP_TIME=%272116-Apr-13%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27|access-date=February 28, 2025}}</ref>

<ref name="Horizons2117">{{cite web|title=Horizons Batch for Apophis @ 2117-Oct-07 17:21 showing 3-sigma uncertainty of ±42 million km|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272117-Oct-07%2017:21%27&STOP_TIME=%272117-Oct-08%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27|access-date=February 28, 2025}}</ref>

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<ref name="SETI2021">{{cite web|title=We Got it! The Story of Astronomers and Citizen Astronomers Catching Hazardous Apophis Asteroid over Colorado and Louisiana|publisher=[[SETI Institute]]|first=F.|last=Marchis|url=https://www.seti.org/we-got-it|archive-url=https://web.archive.org/web/20210310222038/https://www.seti.org/we-got-it|date=March 10, 2021|archive-date=March 10, 2021|url-status=live|access-date=March 13, 2021}}</ref>

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<ref name="Occultation award">{{cite web|title=Lifetime Achievement Award of the International Occultation Timing Association|url=https://www.asteroidoccultation.com/observations/Awards/Venable.html|date=2021|website=asteroidoccultation.com|publisher=International Occultation Timing Association|access-date=November 27, 2021}}</ref>
 
<ref name="JOA2021_3">{{cite journal|title=Chasing the Shadow of (99942) Apophis|url=https://iota-es.de/JOA/JOA2021_3.pdf|year=2021|journal=Journal of Occultation Astronomy|volume=11|issue=3|pages=1–2, 24–29|access-date=November 27, 2021}}</ref>

<ref name="Wayback2005-02">{{cite web|title=2004 MN4 Earth Impact Risk Summary|publisher=NASA/JPL|url=http://neo.jpl.nasa.gov/risk/2004mn4.html|date=February 5, 2005|access-date=January 13, 2013|url-status=dead|archive-url=https://web.archive.org/web/20050206005155/http://neo.jpl.nasa.gov/risk/2004mn4.html|archive-date=February 6, 2005}}</ref>

<ref name="Wayback2005-10">{{cite web|title=99942 Apophis Earth Impact Risk Summary|publisher=NASA JPL|url=http://neo.jpl.nasa.gov/risk/a99942.html|date=October 18, 2005|access-date=January 13, 2013|url-status=dead|archive-url=https://web.archive.org/web/20051018181735/http://neo.jpl.nasa.gov/risk/a99942.html|archive-date=October 18, 2005}}</ref>

<ref name="Wayback2006-07">{{cite web|title=99942 Apophis (2004 MN4) Earth Impact Risk Summary|publisher=NASA/JPL|url=http://neo.jpl.nasa.gov/risk/a99942.html|date=July 1, 2006|access-date=January 13, 2013|url-status=dead|archive-url=https://web.archive.org/web/20060701215601/http://neo.jpl.nasa.gov/risk/a99942.html|archive-date=July 1, 2006}}</ref>

<ref name="Wayback2006-08">{{cite web|title=99942 Apophis (2004 MN4) Earth Impact Risk Summary|publisher=NASA/JPL|url=http://neo.jpl.nasa.gov/risk/a99942.html|date=August 5, 2006|access-date=January 13, 2013|url-status=dead|archive-url=https://web.archive.org/web/20060805063943/http://neo.jpl.nasa.gov/risk/a99942.html|archive-date=August 5, 2006}}</ref>

<ref name="Wayback2013-01">{{cite web|title=99942 Apophis (2004 MN4) Earth Impact Risk Summary|publisher=NASA/JPL|url=http://neo.jpl.nasa.gov/risk/a99942.html|date=May 6, 2013|access-date=March 13, 2021|url-status=dead|archive-url=https://web.archive.org/web/20130110015803/http://neo.jpl.nasa.gov/risk/a99942.html|archive-date=January 10, 2013}}</ref>
 
<ref name="Reddy2022">{{cite journal|title=Apophis Planetary Defense Campaign|first1=Vishnu|last1=Reddy|first2=Michael S.|last2=Kelley|first3=Jessie|last3=Dotson|first4=Davide|last4=Farnocchia|display-authors=etal|date=May 31, 2022|journal=The Planetary Science Journal|volume=3|issue=5|page=123|doi=10.3847/PSJ/ac66eb|bibcode=2022PSJ.....3..123R|s2cid=249227833|doi-access=free}}</ref>
 
<ref name="Satpathy2022">{{cite journal|title=NEOWISE Observations of the Potentially Hazardous Asteroid (99942) Apophis|first1=Akash|last1=Satpathy|first2=Amy|last2=Mainzer|first3=Joseph R.|last3=Masiero|first4=Tyler|last4=Linder|display-authors=etal|date=May 31, 2022|journal=The Planetary Science Journal|volume=3|issue=5|page=124|doi=10.3847/PSJ/ac66d1|arxiv=2204.05412|bibcode=2022PSJ.....3..124S|s2cid=248118987|doi-access=free}}</ref>
 
<ref name="PlanetaryDefense2021">{{cite web|title=Planetary Defense Exercise Uses Apophis as Hazardous Asteroid Stand-In|url=https://www.nasa.gov/feature/jpl/planetary-defense-exercise-uses-apophis-as-hazardous-asteroid-stand-in|date=May 31, 2022|publisher=NASA|editor=Tony Greicius|access-date=June 1, 2022}}</ref>

<ref name="NeptuneVLTAdaptiveOptics">{{cite web|title=Neptune from the VLT with and without adaptive optics|url=https://www.eso.org/public/usa/images/eso1824b/|date=July 18, 2018|publisher=ESO|access-date=October 17, 2022}}</ref>

}}

== External links ==
{{Commons}}
* {{cite journal|arxiv=1404.5847|doi=10.1051/0004-6361/201423841|bibcode=2014A&A...566A..22M|title=Thermal infrared observations of asteroid (99942) Apophis with ''Herschel''|year=2014|last1=Müller|first1=T. G.|last2=Kiss|first2=C.|last3=Scheirich|first3=P.|last4=Pravec|first4=P.|last5=o'Rourke|first5=L.|last6=Vilenius|first6=E.|last7=Altieri|first7=B.|journal=Astronomy & Astrophysics|volume=566|pages=A22|s2cid=119282830|display-authors=4}}
* [https://web.archive.org/web/20130317183119/http://apophisasteroid.net/ Apophis Asteroid]
* [http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-1212.pdf Asteroid Apophis orbit from recent observations], EPSC Abstracts Vol. 6, EPSC-DPS2011-1212, 2011, EPSC-DPS Joint Meeting 2011
* [http://www.brera.mi.astro.it/sormano/Apophis/Sormano_Apophis.html Diagrams and orbits of Apophis] (Sormano Astronomical Observatory)
* [https://web.archive.org/web/20200611222254/https://gravitysimulator.org/solar-system/apophis-2029-earth-encounter/ Interactive 3D gravity simulation of Apophis's 2029 Earth flyby]

'''Risk assessment'''
* [https://cneos.jpl.nasa.gov/doc/apophis/ Apophis Orbital Prediction Page at NASA JPL]
* [https://newton.spacedys.com/neodys/index.php?pc=1.1.0&n=99942 99942 Apophis page] from [[NEODyS]]
* [http://www.brera.mi.astro.it/sormano/mbpl.html MBPL – Minor Body Priority List (technical List) at Sormano Observatory]
* [http://www.brera.mi.astro.it/sormano/teca.html TECA – Table of Asteroids Next Closest Approaches to the Earth at Sormano Observatory]

'''NASA'''
* [https://web.archive.org/web/20041228072731/http://neo.jpl.nasa.gov/news/news148.html Possibility of an Earth Impact in 2029 Ruled Out for Asteroid {{mp|2004 MN|4}}] (JPL)
* [https://cneos.jpl.nasa.gov/news/news149.html Radar Observations Refine the Future Motion of Asteroid {{mp|2004 MN|4}}] (JPL)
* [https://web.archive.org/web/20041102064506/http://neo.jpl.nasa.gov/gif/mea-orbit-big.gif Animation explaining how impact risk is determined] from [https://web.archive.org/web/20160106045208/http://neo.jpl.nasa.gov/cgi-bin/ip?1 Impact Probability]
* {{JPL small body|id=99942}}

{{s-start}}
{{s-bef|before={{mpl|(153814) 2001 WN|5}}}}
{{s-ttl|title=Large [[Near-Earth object|NEO]] Earth close approach<br />([[List of record-setting asteroid close approaches to Earth#Asteroids|inside the orbit of the Moon]])|years=April 13, 2029}}
{{s-aft|after={{mpl|2012 UE|34}}}}
{{end}}

{{Planetary defense}}
{{Minor planets navigator |99941 Lonniewege |number=99942 |(99943) 2005 AS2}}
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{{DEFAULTSORT:Apophis}}
[[Category:Aten asteroids|099942]]
[[Category:Discoveries by Roy A. Tucker]]
[[Category:Discoveries by David J. Tholen]]
[[Category:Discoveries by Fabrizio Bernardi]]
[[Category:Named minor planets]]
[[Category:Potentially hazardous asteroids|099942]]
[[Category:Radar-imaged asteroids|099942]]
[[Category:Earth-crossing asteroids]]
[[Category:Near-Earth objects removed from the Sentry Risk Table|099942]]
[[Category:Astronomical objects discovered in 2004|20040619]]
[[Category:Minor planets to be visited by spacecraft]]
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