99942 Apophis
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99942 Apophis is a near-Earth asteroid and
potentially hazardous asteroid A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are ...
with a diameter of that caused a brief period of concern in December 2004 when initial observations indicated a probability up to 2.7% that it would hit
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth in 2029. Until 2006, a small probability nevertheless remained that, during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole of no more than about in diameter, which would have set up a future impact exactly seven years later on April 13, 2036. This possibility kept it at Level 1 on the 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' rating on the Torino scale was lowered to zero. By 2008, the keyhole had been determined to be less than 1 km wide. 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 4 on December 27, 2004. The diameter of Apophis is estimated to be approximately . Preliminary observations by Goldstone radar in January 2013 effectively ruled out the possibility of an Earth impact by Apophis in 2036. By May 6, 2013 (April 15, 2013, observation arc), the possibility of an impact on April 13, 2036 had been eliminated altogether. Apophis will make two modestly close approaches to Earth in 2036, but even the planet
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
will come closer to Earth in 2036. On April 12, 2068, the nominal trajectory has Apophis from Earth. Entering March 2021, six asteroids each had a more notable cumulative
Palermo Technical Impact Hazard Scale The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-Earth object (NEO). It combines two types of data—probability of impact and estimated kinetic yield— ...
than Apophis, and none of those has a Torino level above 0. On average, an asteroid the size of Apophis (370 metres) is expected to impact Earth once in about 80,000 years. Observations in 2020 by the Subaru telescope confirmed David Vokrouhlický's 2015
Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10  ...
predictions. The
Goldstone radar The Goldstone Deep Space Communications Complex (GDSCC), commonly called the Goldstone Observatory, is a satellite ground station located in Fort Irwin in the U.S. state of California. Operated by NASA's Jet Propulsion Laboratory (JPL), its m ...
observed Apophis March 3–11, 2021, helping to refine the orbit again, and on March 25, 2021, the
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
announced that Apophis has no chance of impacting Earth in the next 100 years. The uncertainty in the 2029 approach distance has been reduced from hundreds of kilometers to now just a couple of kilometers, greatly enhancing predictions of future approaches. Apophis was removed altogether from the
Sentry Risk Table Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ y ...
the next day.Removed Objects
from Sentry Risk Table


Discovery and naming

Apophis was discovered on June 19, 2004, by Roy A. Tucker,
David J. Tholen David James Tholen (born 1955) is an American astronomer at the Institute for Astronomy of the University of Hawaii. He holds a 1984 PhD from the University of Arizona, and specializes in planetary and Solar System astronomy. He is a discovere ...
, and
Fabrizio Bernardi Fabrizio Bernardi (born 1972) is an Italian astronomer and discoverer of minor planets and comets, best known for the co-discovery of the near-Earth and potentially hazardous asteroid 99942 Apophis. He is a member of the IAU, and credited by t ...
at the
Kitt Peak National Observatory The Kitt Peak National Observatory (KPNO) is a United States astronomical observatory located on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono Oʼodham Nation, west-southwest of Tucson, Arizona. With more than ...
. On December 21, 2004, Apophis passed from Earth. Precovery observations from March 15, 2004, were identified on December 27, and an improved orbit solution was computed.
Radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...
astrometry in January 2005 further refined its orbit solution. The discovery was notable in that it was at a very low solar elongation (56°) and at very long range (1.1 AU). See diagram below: When first discovered, the object received the provisional designation , 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 24, 2005). Receiving a permanent number made it eligible for naming by its discoverers, and they chose the name "Apophis" on July 19, 2005. Apophis is the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
name of Apep, an enemy of the Ancient Egyptian sun-god Ra. He is the Uncreator, an evil serpent that dwells in the eternal darkness of the
Duat The Duat ( egy, dwꜣt, Egyptological pronunciation "do-aht", cop, ⲧⲏ, also appearing as ''Tuat'', ''Tuaut'' or ''Akert'', ''Amenthes'', ''Amenti'', or ''Neter-khertet'') is the realm of the dead in ancient Egyptian mythology. It has been ...
and tries to swallow Ra during his nightly passage. Apep is held at bay by
Set Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements *Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electro ...
, the Ancient Egyptian god of storms and the desert. Tholen and Tucker, two of the co-discoverers of the asteroid, are reportedly fans of the television series ''
Stargate SG-1 ''Stargate SG-1'' (often stylized in all caps, or abbreviated ''SG-1'') is a military science fiction adventure television series within Metro-Goldwyn-Mayer's ''Stargate'' franchise. The show, created by Brad Wright and Jonathan Glassner, ...
''. One of the show's persistent villains is an alien named 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. The mythological creature Apophis is pronounced with the accent on the first syllable (/ˈæpəfɪs/). In contrast, the asteroid's name is generally accented on the second syllable (/əˈpɒfɪs/) as the name was pronounced in the TV series.


Physical characteristics

Based upon the observed brightness, Apophis's diameter was initially estimated at ; a more refined estimate based on spectroscopic observations at
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
's Infrared Telescope Facility in Hawaii by Binzel, Rivkin, Bus, and Tokunaga (2005) is . NASA's impact risk page lists the diameter at and lists a mass of 4 kg based on an assumed density of 2.6 g/cm. The mass estimate is more approximate than the diameter estimate, but should be accurate to within a factor of three. Apophis's surface composition probably matches that of
LL chondrite The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls (see meteorite fall statistics). The ordi ...
s. Based on Goldstone and Arecibo radar images taken in 2012–2013, Brozović et al. have estimated that Apophis is an elongated object 450 × 170 metres in size, and that it is bilobed (possibly a
contact binary In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overconta ...
) with a relatively bright surface albedo of . Its rotation axis has an
obliquity In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbi ...
of −59° against the
ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...
, which means that Apophis is a retrograde rotator. During the 2029 approach, Apophis's brightness will peak at
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
 3.1, easily visible to the naked eye if one knows where to look, with a maximum angular speed of 42° per hour. The maximum apparent
angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...
will be ~2  arcseconds. This is roughly equivalent to the
angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...
of Neptune from earth. Therefore, the asteroid will be barely resolved by ground-based telescopes not equipped with
adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...
but very well resolved by those that are. Due to the closeness of the approach, it is likely that
tidal forces The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...
will alter Apophis's rotation axis. A partial resurfacing of the asteroid is possible, which might change its spectral class from a
weathered ''Weathered'' is the third studio album by American rock band Creed, released on November 20, 2001. It was the last Creed album to be released until '' Full Circle'' came out in October 2009, with Creed disbanding in June 2004. It is the only Cr ...
Sq- to an unweathered Q-type.


Orbit

Apophis has a low inclination orbit (3.3°) that varies from just outside the orbit of
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
(0.746 AU) to just outside the orbit of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
(1.099 AU). After the 2029 Earth approach the orbit will vary from just inside of Earth's to just inside of Mars.


2029 close approach

The closest known approach of Apophis occurs at April 13, 2029 21:46 UT, when Apophis will pass Earth closer than
geosynchronous A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...
communication satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...
s, but will come no closer than above Earth's surface.2029-Apr-13 approach:
38012km "geocentric distance"
– 6378km "
Earth radius Earth radius (denoted as ''R''🜨 or R_E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly (equatorial radius, deno ...
" = 31634km
Using the June 2021 orbit solution which includes the
Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10  ...
, the 3-sigma uncertainty region in the 2029 approach distance is about ±3.4 km. The distance, a hair's breadth in astronomical terms, is five times the
radius of the Earth Earth radius (denoted as ''R''🜨 or R_E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly (equatorial radius, deno ...
, ten times closer than the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, and closer than more than 500 geostationary satellites currently orbiting the earth. It will be the closest asteroid of its size in recorded history. On that date, it will become as bright as magnitude 3.1 (visible to the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
from rural as well as darker suburban areas, visible with binoculars from most locations). The close approach will be visible from
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
,
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, and western
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
. During the approach, Earth will
perturb Perturbation or perturb may refer to: * Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly * Perturbation (geology), changes in the nature of alluvial deposits over time * Perturbatio ...
Apophis from an
Aten Aten also Aton, Atonu, or Itn ( egy, jtn, ''reconstructed'' ) was the focus of Atenism, the religious system established in ancient Egypt by the Eighteenth Dynasty pharaoh Akhenaten. The Aten was the disc of the sun and originally an aspect o ...
-class orbit with a semi-major axis of 0.92  AU to an
Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label= Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label ...
-class orbit with a semi-major axis of 1.1 AU.
Perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...
will lift from 0.746 AU to 0.894 AU and aphelion will lift from 1.099 AU to 1.31 AU.


2036 approaches

In 2036 Apophis will approach the Earth at a third the distance of the Sun in both March and December. Using the 2021 orbit solution, the Earth approach on March 27, 2036, will be no closer than , but more likely about . The planet Venus will be closer to Earth at on May 30, 2036.


2051 approach

Around April 19–20, 2051, Apophis will pass about from Earth and it will be the first time since 2029 that Apophis has passed within 10 million km of Earth.


2066/2068

In the 2060s Apophis will approach Earth in September 2066, and then from February 2067 to December 2071 Apophis will remain further from Earth than the Sun is. On April 12, 2068,
JPL Horizons JPL Horizons On-Line Ephemeris System provides access to key Solar System data and flexible production of highly accurate ephemerides for Solar System objects. Osculating elements at a given epoch (such as produced by the JPL Small-Body Databas ...
calculates that Apophis will be about from Earth, making the asteroid much further than the Sun. By 2116 the
JPL Small-Body Database The JPL Small-Body Database (SBDB) is an astronomy database about small Solar System bodies. It is maintained by Jet Propulsion Laboratory (JPL) and NASA and provides data for all known asteroids and several comets, including orbital parameters an ...
and
NEODyS NEODyS (Near Earth Objects Dynamic Site) is an Italian service that provides information on near-Earth objects with a Web-based interface. It is based on a continually and (almost) automatically maintained database of near earth asteroid orbits. T ...
close approach data start to become divergent. In April 2116 Apophis is expected to pass about from Earth, but could pass as close as or could pass as far as .


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 Sentry or The Sentry may refer to: Comics *Sentry (Kree) *Sentry (Curtis Elkins) * Sentry (Robert Reynolds) *Senator Ward (comics) or Sentry Vehicles *Sentry (AUV), an autonomous underwater vehicle used to measure deep-ocean data *E-3 Sentry AWAC ...
system and
NEODyS NEODyS (Near Earth Objects Dynamic Site) is an Italian service that provides information on near-Earth objects with a Web-based interface. It is based on a continually and (almost) automatically maintained database of near earth asteroid orbits. T ...
, a similar automatic program run by the
University of Pisa The University of Pisa ( it, Università di Pisa, UniPi), officially founded in 1343, is one of the oldest universities in Europe. History The Origins The University of Pisa was officially founded in 1343, although various scholars place ...
and the
University of Valladolid The University of Valladolid is a public university located in the city of Valladolid, Valladolid province, autonomous region of Castile and Leon, Spain. Established in the 13th century, it is one of the oldest universities in the world. The u ...
. Subsequent observations decreased the uncertainty in Apophis's trajectory. The probability of an impact event in 2029 temporarily climbed, peaking at 2.7% (1 in 37) on December 27, 2004, when the uncertainty region had shrunk to 83,000 km. This probability, combined with its size, caused Apophis to be assessed at level 4 on the
Torino scale The Torino scale is a method for categorizing the impact hazard associated with near-Earth objects (NEOs) such as asteroids and comets. It is intended as a communication tool for astronomers and the public to assess the seriousness of collision pre ...
and 1.10 on the
Palermo Technical Impact Hazard Scale The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-Earth object (NEO). It combines two types of data—probability of impact and estimated kinetic yield— ...
, scales scientists use to represent how dangerous a given asteroid is to Earth. These are the highest values for which any object has been rated on either scale. The chance that there would be an impact in 2029 was eliminated by late December 27, 2004, as a result of a precovery image that extended the observation arc back to March 2004. The danger of a 2036 passage was lowered to level 0 on the Torino scale in August 2006. With a cumulative Palermo Scale rating of −3.22, the risk of impact from Apophis is less than one thousandth the background hazard level.


2005 and 2011 observations

In July 2005, former
Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label= Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label ...
astronaut
Rusty Schweickart Russell Louis "Rusty" Schweickart (also Schweikart; born October 25, 1935) is an American aeronautical engineer, and a former NASA astronaut, research scientist, U.S. Air Force fighter pilot, as well as a former business executive and governme ...
, as chairman of the
B612 Foundation The B612 Foundation is a private nonprofit foundation headquartered in Mill Valley, California, United States, dedicated to planetary science and planetary defense against asteroids and other near-Earth object (NEO) impacts. It is led mainl ...
, formally asked NASA to investigate the possibility that the asteroid's post-2029 orbit could be in
orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
with Earth, which would increase the probability of future impacts. Schweickart also asked NASA to investigate whether a
transponder In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight trans ...
should be placed on the asteroid to enable more accurate tracking of how its orbit is affected by the
Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10  ...
. On January 31, 2011, astronomers took the first new images of Apophis in more than 3 years.


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 he next good opportunity we should be able to predict the location of out to at least 2070." Apophis passed within of Earth in 2013, allowing astronomers to refine the trajectory for future close passes. Just after the closest approach on January 9, 2013, the asteroid peaked at an
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
of about 15.6. The Goldstone radar observed Apophis during that approach from January 3 through January 17. The Arecibo Observatory observed Apophis once it entered Arecibo's declination window after February 13, 2013. 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. 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).


2015 observations

As of January 2019, Apophis had not been observed since 2015, mostly because its orbit has 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.


2020–21 observations

No observations of Apophis were made between January 2015 and February 2019, and then observations started occurring regularly in January 2020. In March 2020, astronomers David Tholen and Davide Farnocchia measured the acceleration of Apophis due to the
Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10  ...
for the first time, significantly improving the prediction of its orbit past the 2029 flyby. Tholen and Farnocchia found that the Yarkovsky effect caused Apophis to drift by about 170 meters per year. In late 2020, Apophis approached the Earth again. It passed from Earth on March 6, 2021, brightening to +15
mag Mag, MAG or mags may refer to: Arts, entertainment and media * ''MAG'' (video game), 2010 * ''Mag'' (Slovenian magazine), 1995–2010 * '' The Mag'', a British music magazine Businesses and organisations * MacKenzie Art Gallery, in Regina, Sask ...
at the time. Radar observations of Apophis were planned at Goldstone in March 2021. The asteroid has been observed by
NEOWISE Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 201 ...
(between December 2020 and April 2021) and by NEOSSat (in January 2021). Apophis was the target of an observing campaign by IAWN, resulting in the collection of
light curves In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...
, spectra, and astrometry. The observations were used to practice and coordinate the response to an actual impact threat. On February 21, 2021, Apophis was removed from the
Sentry Risk Table Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ y ...
, as an impact in the next 100 years was finally ruled out. Several
occultations An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
of bright stars (
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
8-11) by Apophis occurred in March and April 2021. A total of five separate occultations were observed successfully, marking the first time that an asteroid as small as Apophis was observed using the occultation method (beating the previous record set in 2019 by asteroid 3200 Phaeton by more than a factor of ten). The first event, on March 7, was successfully observed from the United States by multiple observers. The next potential occultation, which occurred on March 11, was predicted to be visible from central Europe. This event was missed, mainly due to bad weather (two negative observations were recorded from
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders ...
). On March 22, another occultation was observed only by a single observer from the United States,
amateur astronomer Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers ...
Roger Venable. Due to larger-than-expected residuals in the March 7 data, the majority of observers had been deployed outside of the actual path for the March 22 occultation. 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 ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ke ...
, again by Venable, alongside others. Two more occultations, observable on April 10 and April 11 from Japan and New Mexico, respectively, were seen by several observers each. 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, Apophis became the asteroid with the most precisely measured Yarkovsky effect of all asteroids, at a signal-to-noise ratio (SNR) of 186.4, surpassing
101955 Bennu 101955 Bennu (provisional designation ) is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on 11 September 1999. It is a potentially hazardous object that is listed on the Sentry Risk Table and has the highest cumul ...
(SNR=181.6). The 2021 apparition was the last opportunity to observe Apophis before its 2029 flyby.


History of impact estimates


Possible impact effects

The Sentry Risk Table estimates that Apophis would impact Earth with
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acc ...
equivalent to 1,200  megatons of TNT. In comparison, the
Chicxulub impact The Chicxulub crater () is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore near the community of Chicxulub, after which it is named. It was formed slightly over 66 million years ago when a large a ...
which caused the mass extinction event responsible for wiping out the dinosaurs has been estimated to have released about as much energy as 100,000,000 megatons (100 teratons). The exact effects of any impact would vary based on the asteroid's composition, and the location and angle of impact. Any impact 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 An impact winter is a hypothesized period of prolonged cold weather due to the impact of a large asteroid or comet on the Earth's surface. If an asteroid were to strike land or a shallow body of water, it would eject an enormous amount of dust, ...
. Assuming Apophis is a stony asteroid with a density of 3,000 kg/m3, if it were to impact into
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
, Apophis would create a
impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
.


Expired 2036 path of risk

In 2008, the
B612 Foundation The B612 Foundation is a private nonprofit foundation headquartered in Mill Valley, California, United States, dedicated to planetary science and planetary defense against asteroids and other near-Earth object (NEO) impacts. It is led mainl ...
made estimates of Apophis's path if a 2036 Earth impact were to occur, as part of an effort to develop viable deflection strategies. The result was a narrow corridor a few kilometres wide, called the "path of risk", extending across southern
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
, across the north
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
(relatively close to the coastlines of
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
and
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
), then right between
Nicaragua Nicaragua (; ), officially the Republic of Nicaragua (), is the largest country in Central America, bordered by Honduras to the north, the Caribbean to the east, Costa Rica to the south, and the Pacific Ocean to the west. Managua is the countr ...
and Costa Rica, crossing northern Colombia and
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
, ending in the
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
, just before reaching
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. 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. A deep-water impact in the Atlantic or Pacific oceans would produce an incoherent short-range
tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...
with a potential destructive radius (inundation height of >2 m) of roughly for most of North America, Brazil and Africa, for Japan and for some areas in Hawaii.


Exploration


OSIRIS-APEX post-Earth-encounter rendezvous

The ''
OSIRIS-REx OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is a NASA asteroid-study and sample-return mission. The mission's primary goal is to obtain a sample of at least from 101955 Bennu, a carbona ...
'' spacecraft is expected to return a sample of
Bennu Bennu is an ancient Egyptian deity linked with the Sun, creation, and rebirth. He may have been the original inspiration for the phoenix legends that developed in Greek mythology. Roles According to Egyptian mythology, Bennu was a self-create ...
to Earth in 2023. 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 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. For its Apophis mission after the sample return, ''OSIRIS-REx'' will be renamed ''OSIRIS-APEX'' (short for OSIRIS-Apophis Explorer).


Other proposed space missions


Planetary Society competition

In 2007, The
Planetary Society The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, a ...
, a
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
-based space advocacy group, organized 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 entries from 20 countries on 6 continents. The commercial competition was won by a design called 'Foresight' created by
SpaceWorks Enterprises, Inc. SpaceWorks Enterprises, Inc. (SEI) is an aerospace engineering company based in Atlanta, Georgia (U.S. state), Georgia, United States that specializes in the design, assessment, hardware prototyping and flight demonstration of advanced space conce ...
SpaceWorks proposed a simple orbiter with only two instruments and a radio beacon at a cost of ~US$140 million, launched aboard a
Minotaur IV Minotaur IV, also known as Peacekeeper SLV and OSP-2 PK is an active expendable launch system derived from the LGM-118 Peacekeeper ICBM. It is operated by Northrop Grumman Innovation Systems, and made its maiden flight on 22 April 2010, carry ...
between 2012 and 2014, to arrive at Apophis five to ten months later. It would then rendezvous with, observe, and track the asteroid. Foresight would orbit the asteroid to gather data with a
multi-spectral image Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, ...
r for one month. It would then leave orbit and fly in formation with Apophis around the Sun at a range of . The spacecraft would use laser ranging to the asteroid and radio tracking from Earth for ten months to accurately determine the asteroid's orbit and how it might change. Pharos, the winning student entry, would be an orbiter with four science instruments (a multi-spectral imager, near-infrared spectrometer, laser rangefinder, and magnetometer) that would rendezvous with and track Apophis. Earth-based tracking of the spacecraft would then allow precise tracking of the asteroid. The Pharos spacecraft would also carry four instrumented probes that it would launch individually over the course of two weeks.
Accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acc ...
s and temperature sensors on the probes would measure the seismic effects of successive probe impacts, a creative way to explore the interior structure and dynamics of the asteroid. Second place, for $10,000, went to a European team led by Deimos Space S.L. of
Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 6.7 million. It is the Largest cities of the Europ ...
,
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
, in cooperation with EADS
Astrium Astrium was an aerospace manufacturer subsidiary of the European Aeronautic Defence and Space Company (EADS) that provided civil and military space systems and services from 2006 to 2013. In 2012, Astrium had a turnover of €5.8 billion and 1 ...
, Friedrichshafen, Germany; University of Stuttgart, Germany; and
University of Pisa The University of Pisa ( it, Università di Pisa, UniPi), officially founded in 1343, is one of the oldest universities in Europe. History The Origins The University of Pisa was officially founded in 1343, although various scholars place ...
, Italy. Juan L. Cano was
principal investigator In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often us ...
. Another European team took home $5,000 for third place. Their team lead was EADS Astrium Ltd, United Kingdom, in conjunction with EADS Astrium SAS, France; IASF-Roma, INAF, Rome, Italy;
Open University The Open University (OU) is a British public research university and the largest university in the United Kingdom by number of students. The majority of the OU's undergraduate students are based in the United Kingdom and principally study off- ...
, UK; Rheinisches Institut für Umweltforschung, Germany;
Royal Observatory of Belgium The Royal Observatory of Belgium (french: link=no, Observatoire Royal de Belgique, nl, Koninklijke Sterrenwacht van België), has been situated in the Uccle municipality of Brussels (Belgium) since 1890. It was first established in Saint-Josse ...
; and
Telespazio Telespazio Spa is a European spaceflight services company founded in 1961. It is a joint venture owned by Leonardo (67%) and Thales Group (33%) headquartered in Rome. Telespazio provides services that include the design and development of space ...
, Italy. The principal investigator was Paolo D'Arrigo. Two teams tied for second place in the Student
Monash University Monash University () is a public research university based in Melbourne, Victoria, Australia. Named for prominent World War I general Sir John Monash, it was founded in 1958 and is the second oldest university in the state. The university h ...
, Clayton Campus, Australia, with Dilani Kahawala as principal investigator; and
University of Michigan , mottoeng = "Arts, Knowledge, Truth" , former_names = Catholepistemiad, or University of Michigania (1817–1821) , budget = $10.3 billion (2021) , endowment = $17 billion (2021)As o ...
, with Jeremy Hollander as principal investigator. Each second-place team won $2,000. A team from Hong Kong Polytechnic University and
Hong Kong University of Science and Technology The Hong Kong University of Science and Technology (HKUST) is a public research university in Clear Water Bay Peninsula, New Territories, Hong Kong. Founded in 1991 by the British Hong Kong Government, it was the territory's third institut ...
, under the leadership of Peter Weiss, received an honorable mention and $1,000 for the most innovative student proposal.


Don Quijote mission

Apophis is one of two asteroids that were considered by the European Space Agency as the target of its Don Quijote mission concept to study the effects of impacting an asteroid.


Cancelled 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 '' ZhengHe'', would have included exploration and close study of three asteroids including an extended encounter with Apophis for close observation, and land on the asteroid 1996 FG3 to conduct in situ sampling analysis on the surface. The launch date is now scheduled for 2024, with a different set of targets.


Proposed deflection strategies

Studies by NASA, ESA, and various research groups in addition to the Planetary Society contest teams, have described a number of proposals for deflecting Apophis or similar objects, including gravitational tractor, kinetic impact, and nuclear bomb methods. On December 30, 2009,
Anatoly Perminov Anatoly Nikolayevich Perminov (russian: Анатолий Николаевич Перминов; born 16 June 1945) is a Russian rocket scientist and a mechanical engineer. He served as the General Director of Russian Federal Space Agency in 2004 ...
, the director of the Russian Federal Space Agency, said in an interview that
Roscosmos The State Space Corporation "Roscosmos" (russian: Государственная корпорация по космической деятельности «Роскосмос»), commonly known simply as Roscosmos (russian: Роскосмос) ...
will also study designs for a possible deflection mission to Apophis. On August 16, 2011, researchers at China's
Tsinghua University Tsinghua University (; abbr. THU) is a national public research university in Beijing, China. The university is funded by the Ministry of Education. The university is a member of the C9 League, Double First Class University Plan, Projec ...
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. On February 15, 2016, Sabit Saitgarayev, of the Makeyev Rocket Design Bureau, announced intentions to use
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
n ICBMs to target relatively small
near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...
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. In October 2022, a method of mapping the insides of a potentially problematic asteroid, such as 99942 Apophis, in order to determine the best area for impact was proposed.


Popular culture

In
Id Software id Software LLC () is an American video game developer based in Richardson, Texas. It was founded on February 1, 1991, by four members of the computer company Softdisk: game programmer, programmers John Carmack and John Romero, game designer T ...
's
video game Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, controller, keyboard, or motion sensing device to generate visual feedback. This fee ...
'' 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 Apocalyptic and post-apocalyptic fiction is a subgenre of speculative fiction in which the Earth's (or another planet's) civilization is collapsing or has collapsed. The apocalypse event may be climatic, such as runaway climate change; ast ...
age.
The
Enter Shikari Enter Shikari (stylised as enter: shikari and occasionally as ΣΠΤΣ℞ SΗΦΚ∆℞Φ) are a British rock band formed in St Albans, Hertfordshire, England in 1999 by bassist Chris Batten, lead vocalist and keyboardist Rou Reynolds, and dr ...
song, 'Zzzonked' makes reference to the asteroid in the second verse. The
Type O Negative Type O Negative were an American gothic metal band formed in Brooklyn, New York City in 1989 by Peter Steele (bass, lead vocals), Kenny Hickey (guitar, co-lead vocals), Josh Silver (keyboards, backing vocals), and Sal Abruscato (drums, percu ...
song "The Profit Of Doom" references the asteroid. The
cleopatrick Cleopatrick (stylized in lowercase) is a Canadian rock duo based out of Cobourg, Ontario. They have their own record label, called Nowhere Special Recordings. Background Childhood friends Ian Fraser and Luke Gruntz grew up in Cobourg, Ontario ...
song “OK” references the asteroid.


See also

*
Asteroid capture Asteroid capture is an orbital insertion of an asteroid around a larger planetary body. When asteroids, small rocky bodies in space, are captured, they become natural satellites. All asteroids entering Earth's orbit or atmosphere so far have been n ...
*
Asteroid impact prediction Asteroid impact prediction is the prediction of the dates and times of asteroids impacting Earth, along with the locations and severities of the impacts. The process of impact prediction follows three major steps: # Discovery of an asteroid and ...
*
Asteroid Redirect Mission The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013; the mission was later cancelled. The Asteroid Retrieval Robotic ...
*
Earth-grazing fireball An Earth-grazing fireball (or Earth grazer) is a fireball, a very bright meteor that enters Earth’s atmosphere and leaves again. Some fragments may impact Earth as meteorites, if the meteor starts to break up or explodes in mid-air. These phenom ...
*
List of impact craters on Earth This list of impact craters on Earth contains a selection of the 190 confirmed craters given in the Earth Impact Database as of 2017. To keep the lists manageable, only the largest craters within a time period are included. Alphabetical lists f ...
*
NEO Surveyor NEO Surveyor, formerly called Near-Earth Object Camera (NEOCam), then NEO Surveillance Mission, is a planned space-based infrared telescope designed to survey the Solar System for potentially hazardous asteroids.Interactive 3D gravity simulation of Apophis's 2029 Earth flyby
Risk assessment
Apophis Orbital Prediction Page at NASA JPL

99942 Apophis page
from
NEODyS NEODyS (Near Earth Objects Dynamic Site) is an Italian service that provides information on near-Earth objects with a Web-based interface. It is based on a continually and (almost) automatically maintained database of near earth asteroid orbits. T ...

MBPL – Minor Body Priority List (technical List) at Sormano Observatory


NASA * ttps://web.archive.org/web/20041228072731/http://neo.jpl.nasa.gov/news/news148.html Possibility of an Earth Impact in 2029 Ruled Out for Asteroid (JPL)
Radar Observations Refine the Future Motion of Asteroid
(JPL)
Animation explaining how impact risk is determined
fro
Impact Probability
* {{DEFAULTSORT:Apophis 099942 Discoveries by Roy A. Tucker Discoveries by David J. Tholen Discoveries by Fabrizio Bernardi Named minor planets 099942 099942 Earth-crosser asteroids 099942 20040619