Jump to content

99942 Apophis

From Wikipedia, the free encyclopedia

99942 Apophis
Model of 99942 Apophis's shape, assuming the entire surface is of a similar composition
Discovery[1]
Discovered by
Discovery siteKitt Peak[1]
Discovery date19 June 2004
Designations
(99942) Apophis
Pronunciation/əˈpɒfɪs/ or /əˈpoʊfɪs/; (trad.) /ˈæpəfɪs/
Named after
Ἄποφις Apophis
2004 MN4
AdjectivesApophidian /æpəˈfɪdiən/ (Latin Apŏpidis)
Symbol (rare)
Orbital characteristics[1]
Epoch 5 May 2025
(JD 2460800.5)
Uncertainty parameter 0
Observation arc6599 days (18.07 yr)
Earliest precovery date15 March 2004
Aphelion1.0987 AU (164.36 million km)
Perihelion0.7461 AU (111.61 million km)
0.9224 AU (137.99 million km)
Eccentricity0.1911
0.886 yr (323.6 d)
30.73 km/s
90.28°
1.112°/day
Inclination3.341°
203.9°
126.7°
Earth MOID0.000038 AU (5.7 thousand km)[1][a]
Jupiter MOID4.1 AU
TJupiter6.464
Physical characteristics
Dimensions
  • 0.370 km (0.230 mi)
  • 0.45 × 0.17 km[3]
  • 0.185 km (0.115 mi)
  • 0.17±0.02 km[3]
Mass6.1×1010 kg (assumed)[4]
Mean density
  • ~3.2 g/cm3[5]
  • 2.6 g/cm3 (assumed)[4]
30.4 h (1.27 d)[1][6]
30.55±0.12 h[7]
30.67±0.06 h[8]
Tumbling:[9]
27.38±0.07 h (precession period),[9] 263±6 h (rotation period),[9] 30.56±0.01 h (twice the period of harmonic with strongest lightcurve amplitude)[9]
Temperature270 K
Sq[6]

99942 Apophis (provisional designation 2004 MN4) is a near-Earth asteroid and a potentially hazardous object, 450 metres (1,480 ft) by 170 metres (560 ft) in size.[3] During a brief period of concern in December 2004, initial observations indicated a probability of 2.7% that the asteroid would hit Earth on Friday, April 13, 2029. Later observations eliminated that possibility of an impact with Earth, and it will pass Earth in 2029 at a distance of about 31,600 km (19,600 mi) above the surface.[12] It will also have a close encounter with the Moon, passing about 89,600 km (55,700 mi) from the lunar surface.[12]

A small possibility remained that during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole estimated to be 800 kilometres in diameter,[13][14] which would have set up a future impact exactly seven years later on Easter Sunday, 13 April 2036.[15] This possibility kept it at Level 1 on the 0 to 10 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 consequently lowered to Level 0. By 2008, the keyhole had been determined to be less than 1 km wide.[13] During the short time when it had been of greatest concern, Apophis set the record for highest rating ever on the Torino scale by reaching Level 4 on 27 December 2004.[16]

It is estimated that an asteroid as big or bigger coming so close to Earth happens only once in 800 years on average.[17][18] Such an asteroid is expected to actually hit Earth once in about 80,000 years.[19]

Preliminary observations by Goldstone radar in January 2013 effectively ruled out the possibility of an Earth impact by Apophis in 2036 (probability less than one in a million).[20] In February 2013 the estimated probability of an impact in 2036 was further reduced to 7×10−9.[2][4] 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,[1] 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. The chance of the Yarkovsky effect having exactly the right value for this was however estimated as two in a million.[2][21] Radar observations in March 2021 helped refine the orbit again,[22] and in March 2021 the Jet Propulsion Laboratory announced that Apophis has no chance of impacting Earth in the next 100 years.[23][24] The uncertainty in the 2029 approach distance has been reduced from hundreds of kilometres to now just a couple of kilometres,[25] 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.[26][b] In the longer term, Apophis will however continue to be a threat for possibly 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

[edit]
Asteroid Apophis — closest approach to Earth on 13 April 2029[27]
(00:20; VideoFile; 29 April 2019) (turquoise dots = artificial satellites; pink = International Space Station)

Apophis was discovered on 19 June 2004, by Roy A. Tucker, David J. Tholen, and Fabrizio Bernardi at the Kitt Peak National Observatory.[1] On 21 December 2004, Apophis passed 0.0964 AU (14.42 Gm; 8.96 million mi) from Earth.[1] Precovery observations from 15 March 2004 were identified on December 27, and an improved orbit solution was computed.[28][29] Radar astrometry in January 2005 further refined its orbit solution.[30][31] The discovery was notable in that it was at a very low solar elongation (56°) and at very long range (1.1 AU).[citation needed]

When first discovered, the object received the provisional designation 2004 MN4, 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 24 June 2005). Receiving a permanent number made it eligible for naming by its discoverers, and they chose the name "Apophis" on 19 July 2005.[32] Apophis is the Greek 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 and tries to swallow Ra during his nightly passage. Apep is held at bay by Set, the Ancient Egyptian god of storms and the desert.[33] Apophis will evolve from an Aten- into an Apollo-type asteroid as a result of the 2029 encounter. Apollo asteroids are usually named after Greek deities, Aten asteroids after Egyptian ones. The name Apophis is a nod to that: It is the Greek name of an Egyptian deity.[34][32]

Atum facing Apep, 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 Apophis. He is one of the principal threats to the existence of civilization on Earth through the first few seasons, and may have inspired the naming.[32] Tholen denied reports that the asteroid was named after the TV character, stating that the connection is coincidental.[34][35] 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.[32]

Proposed symbol for Apophis

The mythological creature Apophis is pronounced with the accent on the first syllable (/ˈæpəfɪs/).[c] In contrast, the asteroid's name is generally accented on the second syllable (/əˈpoʊfɪs/,[36] or /əˈpɒfɪs/ as the name was pronounced in the TV series).[37]

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: 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.[38][39]

Physical characteristics and rotation

[edit]
Comparison between the best-fit convex and nonconvex shape models, and some of the available radar images of (99942) Apophis
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 450 metres (1,480 ft); a more refined estimate based on spectroscopic observations at NASA's Infrared Telescope Facility in Hawaii by Binzel, Rivkin, Bus, and Tokunaga (2005) is 350 metres (1,150 ft). As of 2013, NASA's impact risk page listed the diameter at 330 metres (1,080 ft), and an assumed mass of 4×1010 kg.[4] The mass estimate is more approximate than the diameter estimate, but should be accurate to within a factor of three.[4] Apophis's surface composition probably matches that of LL chondrites.[40]

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) with a relatively bright surface albedo of 0.35±0.10. The axis of its angular momentum points 59° south of the ecliptic, which means that Apophis is a retrograde rotator.[3] Apophis is a 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 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).[9]

Orbit

[edit]
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).[1] Although its orbit changes slightly each time it comes close to 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.[18] 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.[41] At the ascending node (where Apophis crosses the plane of Earth's orbit from south to north) Apophis is very close to where Earth is around 13 April of any year, and this is what gives rise to close encounters such as the one on 13 April 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.[18] After the 2029 Earth approach, the orbit will change dramatically. The period will change from around 8⁄9 of a year to a bit under 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 then pass close to Earth's mid-September location. This will cause a close encounter on 11 September 2102, after which the uncertainty in the location of Apophis will increase rapidly with time.[1]

Selected approaches to Earth until 2117[1]
Date JPL SBDB
nominal geocentric
distance (AU) 		uncertainty
region
(3-sigma)
2004-12-21 0.09638 AU (14.418 million km) n/a
2013-01-09 0.09666 AU (14.460 million km) n/a
2029-04-13 0.000254115 AU (38,015.1 km) ±3.3 km[25]
2036-03-27 0.309678 AU (46.3272 million km) ±130 thousand km[42]
2051-04-20 0.04149 AU (6.207 million km) ±240 thousand km[43]
2066-09-16 0.06943 AU (10.387 million km) ±870 thousand km
2116-04-12 0.01756 AU (2.627 million km) 0.00104 to 0.10433 AU (0.156 to 15.608 million km)[d]
2117-10-07 0.48 AU (72 million km) 0.30994 to 0.64045 AU (46.366 to 95.810 million km)[e]

2029 close approach

[edit]

The closest known approach of Apophis will occur on 13 April 2029, at 21:46 UT, when Apophis will pass Earth at a distance of about 31,600 kilometres (19,600 mi) above the surface.[12] Using the June 2024 orbit solution which includes the Yarkovsky effect, the 3-sigma uncertainty region in the 2029 approach distance is about ±3.3 km.[25][1] The distance, a hair's breadth in astronomical terms, is five times the radius of the Earth, one tenth the distance to the Moon,[46] and closer than the ring of geostationary satellites currently orbiting the Earth.[47][48] It will be the closest asteroid of its size in recorded history. On that date, it will become as bright as magnitude 3.1[49] (visible to the naked eye from rural as well as darker suburban areas, visible with binoculars from most locations).[50] 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 and then southwest to Pisces, an arc of 205°.[51] Approaching Earth its speed relative to Earth will be 6.0 km/s. Earth's gravity will accelerate it to 7.4 km/s at the time of closest approach, and then slow it back down to 6 as it departs.[52] During the approach, Earth will perturb Apophis from an Aten-class orbit with a semi-major axis of 0.92 AU to an Apollo-class orbit with a semi-major axis of 1.1 AU.[53] Perihelion will lift from 0.746 AU to 0.895 AU and aphelion will lift from 1.10 AU to 1.31 AU.[53]

Orbital elements for 2029 (pre-flyby) and 2030 (post-flyby)[53]
Parameter Epoch Orbit
type 		Orbital
period 		Semi-major
axis 		Perihelion Aphelion Inclination Eccentricity
Units AU (°)
Pre-flyby 2029 Aten 0.89 years (323.6 days) 0.922 0.746 1.10 3.34° 0.191
Post-flyby 2030 Apollo 1.16 years (423.1 days) 1.103 0.895 1.31 2.22° 0.189

Apophis also encounters the Moon at 89,600 km (55,700 mi) from the lunar surface, 16 hours after the encounter with Earth.[12]

During the 2029 approach, Apophis's brightness will peak at magnitude 3.1,[49] easily visible to the naked eye, with a maximum angular speed of 42° per hour. The maximum apparent angular diameter will be approximately 2 arcseconds. This is roughly equivalent to the angular diameter of Neptune from Earth. Therefore, the asteroid will be barely resolved by ground-based telescopes not equipped with adaptive optics but very well resolved by those that are.[54] Because the approach will be so close, 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 weathered Sq- to an unweathered Q-type.[3][40]

Animation of 99942 Apophis orbit in 2028–2029
Around Sun
Around Earth
   Sun ·    Earth ·    99942 Apophis  ·    Moon
History of close approaches of large near-Earth objects since 1908 (A)
PHA Date Approach distance in lunar distances Abs. mag
(H) 		Diameter (C)
(m) 		Ref (D)
Nominal(B) Minimum Maximum
(152680) 1998 KJ9 1914-12-31 0.606 0.604 0.608 19.4 279–900 data
(458732) 2011 MD5 1918-09-17 0.911 0.909 0.913 17.9 556–1795 data
(163132) 2002 CU11 1925-08-30 0.903 0.901 0.905 18.5 443–477 data
69230 Hermes 1937-10-30 1.926 1.926 1.927 17.5 700-900[55] data
69230 Hermes 1942-04-26 1.651 1.651 1.651 17.5 700-900[55] data
2017 NM6 1959-07-12 1.89 1.846 1.934 18.8 580–1300 data
(27002) 1998 DV9 1975-01-31 1.762 1.761 1.762 18.1 507–1637 data
2002 NY40 2002-08-18 1.371 1.371 1.371 19.0 335–1082 data
2004 XP14 2006-07-03 1.125 1.125 1.125 19.3 292–942 data
2015 TB145 2015-10-31 1.266 1.266 1.266 20.0 620-690 data
(137108) 1999 AN10 2027-08-07 1.014 1.010 1.019 17.9 556–1793 data
(153814) 2001 WN5 2028-06-26 0.647 0.647 0.647 18.2 921–943 data
99942 Apophis 2029-04-13 0.0981 0.0963 0.1000 19.7 310–340 data
2017 MB1 2072-07-26 1.216 1.215 2.759 18.8 367–1186 data
2011 SM68 2072-10-17 1.875 1.865 1.886 19.6 254–820 data
(163132) 2002 CU11 2080-08-31 1.655 1.654 1.656 18.5 443–477 data
(416801) 1998 MZ 2116-11-26 1.068 1.068 1.069 19.2 305–986 data
(153201) 2000 WO107 2140-12-01 0.634 0.631 0.637 19.3 427–593 data
(276033) 2002 AJ129 2172-02-08 1.783 1.775 1.792 18.7 385–1242 data
(290772) 2005 VC 2198-05-05 1.951 1.791 2.134 17.6 638–2061 data
(A) This list includes near-Earth approaches of less than 2 lunar distances (LD) of objects with H brighter than 20.
(B) Nominal geocentric distance from the center of Earth to the center of the object (Earth has a radius of approximately 6,400 km).
(C) Diameter: estimated, theoretical mean-diameter based on H and albedo range between X and Y.
(D) Reference: data source from the JPL SBDB, with AU converted into LD (1 AU≈390 LD)
(E) Color codes:   unobserved at close approach   observed during close approach   upcoming approaches

2036 approaches

[edit]

In 2036, Apophis will pass the Earth at a third the distance of the Sun in both March and December.[1] Using the 2024 orbit solution, the Earth approach on 27 March 2036, will be no closer than 0.3089 AU (46.21 million km; 28.71 million mi; 120.2 LD), but more likely about 0.3097 AU (46.33 million km; 28.79 million mi).[1] For comparison, the planet Venus will be closer to Earth at 0.2883 AU (43.13 million km; 26.80 million mi; 112.2 LD) on 30 May 2036.[56][f] On 31 December 2036, Apophis will be a little bit further away than the March approach at about 0.33 AU (49 million km; 31 million mi).

2051 approach

[edit]

Around 19–20 April 2051, Apophis will pass about 0.04 AU (6.0 million km; 3.7 million mi) from Earth and it will be the first time since 2029 that Apophis will pass within 10 million km of Earth.[1]

2066 and 2068

[edit]

Although early simulations showed that there was a chance Apophis could hit the earth on 12 April 2068,[2] this was later excluded and JPL Horizons calculates that Apophis will be about 1.864 ± 0.0024 AU (278.85 ± 0.36 million km) from Earth,[57][58] making the asteroid much farther than the Sun.

By 2116, the JPL Small-Body Database and NEODyS close approach data start to become divergent.[1][59] In April 2116, Apophis is expected to pass about 0.02 AU (3 million km; 8 LD) from Earth, but could pass as close as 0.001 AU (150 thousand km; 0.39 LD) or as far as 0.1 AU (15 million km; 39 LD).[1]

Refinement of close approach predictions

[edit]

Six months after discovery, and shortly after a close approach to Earth on 21 December 2004, the improved orbital estimates led to the prediction of a very close approach on 13 April 2029, by both NASA's automatic 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 27 December 2004,[60][61] when the uncertainty region had shrunk to 83,000 km.[62] This probability, combined with its size, caused Apophis to be assessed at level 4 on the Torino scale[16] 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 27 December 2004, as a result of a precovery image that extended the observation arc back to March 2004.[29] The danger of a 2036 passage was lowered to level 0 on the Torino scale in August 2006.[63] With a cumulative Palermo scale rating of −3.22,[4] the risk of impact from Apophis is less than one thousandth the background hazard level.[4]

In July 2005, former 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.[64]

2011 observations

[edit]

On 31 January 2011, astronomers took the first new images of Apophis in more than three years.[65]

Illustration of a common trend where progressively reduced uncertainty regions result in an asteroid impact probability increasing followed by a sharp decrease

2013–2015 refinement

[edit]

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 2004 MN4 out to at least 2070."[66] Apophis passed within 0.0966 AU (14.45 million km; 8.98 million mi) of Earth in 2013, allowing astronomers to refine the trajectory for future close passes.[10][59][67] Just after the closest approach on 9 January 2013,[59] the asteroid peaked at an apparent magnitude of about 15.6.[68] The Goldstone radar observed Apophis during that approach from 3 January through 17 January.[69] The Arecibo Observatory observed Apophis once it entered Arecibo's field of view after 13 February 2013.[69] The 2013 observations basically ruled out any chance of a 2036 impact.

A NASA assessment as of 21 February 2013, that did not use the January and February 2013 radar measurements gave an impact probability of 2.3 in a million for 2068.[70] As of 6 May 2013, using observations through 15 April 2013, the odds of an impact on 12 April 2068, as calculated by the JPL Sentry risk table had increased slightly to 3.9 in a million (1 in 256,000).[4]

Incorporating 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.[71] After 2015, its orbit kept it near the Sun from the perspective of Earth, precluding telescopic observations. It was not further than 60 degrees from the Sun between April 2014 and December 2019.

2020–2021 observations

[edit]
Apophis in February 2021

No observations of Apophis were made between January 2015 and February 2019 but observations began again in January 2020.[72] 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 in time.[73] In late 2020 Apophis approached the Earth and passed 0.11265 AU (16.852 million km; 43.84 LD) from Earth on 6 March 2021, brightening to +15 mag at that time. Radar observations of Apophis were carried out at Goldstone in March 2021.[74][22] The asteroid has been observed by NEOWISE (between December 2020 and April 2021)[75][76] and by NEOSSat (in January 2021).[7][77][8]

These observations showed that the impact parameter 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 km,[74] less than the earlier nominal value of 47,659 km by 296 km because of the Yarkovsky effect. This means that Apophis will not hit Earth in the coming century, in particular avoiding the keyhole 212.14 km below nominal that would have led to a collision in 2068.[2]

Apophis was the target of an observing campaign by the International Asteroid Warning Network, resulting in the collection of light curves, spectra, and astrometry.[7][77][8] 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.[78]

Hypothetical risk corridor for an impact on 13 April 2029, based on the 2020–21 planetary defense exercise

On 21 February 2021, Apophis was removed from the Sentry Risk Table, as an impact in the next 100 years was finally ruled out.[79]

Several occultations of bright stars (apparent magnitude 8–11) by Apophis occurred in March and April 2021.[80][81][82][83] 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 Phaethon, which is more than ten times the size of Apophis).[81] The first event, on 7 March, was successfully observed from the United States by multiple observers.[84][85][80] The next potential occultation, which occurred on 11 March, was predicted to be visible from central Europe,[82] but was not observed, mainly because of bad weather (two negative observations were recorded from Greece).[81] Another occultation occurred on 22 March, but larger-than-expected residuals in the 7 March data had caused the majority of observers to be deployed outside of the actual path for the occultation,[80] and it was observed only by a single observer from the United States, amateur astronomer Roger Venable. This single detection then allowed the prediction of several more events that would have been unobservable otherwise, including an occultation on 4 April, which was observed from New Mexico, again by Venable, alongside others.[83][80] Two more occultations, observable on 10 and 11 April from Japan and New Mexico, respectively, were seen by several observers each.[80] The occultation measurements allowed refinement of the measurement of the asteroid size and orbit.

On 9 March 2021, using radar observations from Goldstone taken on 3–8 March and three positive detections of the stellar occultation on 7 March 2021,[86] Apophis became the asteroid with the most precisely measured Yarkovsky effect of all asteroids, at a signal-to-noise ratio (SNR) of 186.4,[87][g] surpassing 101955 Bennu (SNR=181.6).[88]

The 2021 apparition was the last opportunity to observe Apophis until shortly before its 2029 flyby.[1]

Asteroid 99942 Apophis – radar observations 8–10 March 2021 (26 March 2021)

History of impact estimates

[edit]
Date Time Status
2004-12-23 The original NASA report mentioned impact chances of "around 1 in 300" in 2029, which was widely reported in the media.[16] 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 m to 390 m and its mass from 1.2×1011 kg to 8.3×1010 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 m and 7.5×1010 kg, respectively.
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%)[61] with a line of variation (LOV) of only 83,000 km;[62] diameter was increased to 390 m, and mass to 7.9×1010 kg.
Later that afternoon, a precovery increased the span of observations to 287 days, which eliminated the 2029 impact threat.[29] The cumulative impact probability was estimated to be around 0.004%, a risk lower than that of asteroid 2004 VD17, 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 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.
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 days (2004-Mar-15.1104 to 2004-Dec-29.02821), though the close encounters were changed and reduced to 4 in total.
2004-12-30 13:46 GMT No passes were rated above 0, based upon 157 observations spanning 289.33 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[30] refine the orbit further and show that the April 2029 close approach will occur at only 5.7 Earth radii,[31] 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.[89]
2005-08-07 Radar observation[30] refines the orbit further and eliminates the possibility of an impact in 2035. Only the pass in 2036 remains at Torino scale 1 (with a 1-in-5,560 chance of impact).[90]
2005–10 It is predicted that Apophis will pass just below the altitude of geosynchronous satellites, which are at approximately 35,900 kilometres (22,300 mi).[91] Such a close approach by an asteroid of that size is estimated to occur every 800 years or so.[17]
2006-05-06 Radar observation at Arecibo Observatory[30] slightly lowered the Palermo scale rating, but the pass in 2036 remained at Torino scale 1[92] 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 0.[63] (The impact probability was assessed as 1 in 45,000.)[63]
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.[93] This estimate was allegedly acknowledged by ESA and NASA[94][95][93] but in an official statement,[96] 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 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[97] that shows how unmeasured physical parameters of Apophis bias the entire statistical uncertainty region. If Apophis is a 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.[17][18]
2009-10-07 Refinements to the precovery images of Apophis by the University of Hawaii's Institute for Astronomy, the 90-inch Bok Telescope, and the Arecibo Observatory have generated a refined path that reduces the odds of an 13 April 2036 impact to about 1 in 250,000.[98]
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.[17] Additional factors that could greatly influence the predicted motion in ways that depend on unknown details, were the spin of the asteroid,[99] its precise mass, the way it reflects and absorbs sunlight, radiates heat, and the gravitational pull of other asteroids passing nearby.[17] Small uncertainties in the masses and positions of the planets and Sun could cause up to 23 Earth radii of prediction error for Apophis by 2036.[17]
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.[2] First appearance of Sentry virtual impactors that also include mid-October dates.[100]
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.[10] 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.[10] Goldstone single-pixel observations of Apophis have ruled out the potential 2036 Earth impact.[20][101][102] Apophis will then come no closer than about 23 million kilometres (14×10^6 mi)—and more likely miss us by something closer to 56 million kilometres (35×10^6 mi).[101] The radar astrometry is more precise than was expected.[101]
2014-10-08 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.[103]
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.[73]
2021-02-21 Apophis was removed from the Sentry Risk Table, as an impact in the next 100 years was finally ruled out.[79]
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 km[104] to about ±3 km.[1] The June 2021 solution showed the Earth approach on 27 March 2036 will be no closer than 0.30889 AU (46.209 million km; 28.713 million mi; 120.21 LD).[1]
2024-06-25 JPL solution #220 includes observations through 2022-April-09.[1]

Possible impact effects

[edit]

As of 2021, the Sentry Risk Table estimated that Apophis would impact Earth with kinetic energy equivalent to 1,200 MT or megatons of TNT.[4] In comparison, the energy released by the eruption of Krakatoa was 200 MT, the total global nuclear arsenal has an energy equivalent to 1,460 MT, and the Chicxulub impact and extinction event had an estimated energy of 100,000,000 MT (100 teratons). See 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.[105] Assuming Apophis is a 370-metre-wide (1,210 ft) stony asteroid with a density of 3,000 kg/m3, if it were to impact into sedimentary rock, Apophis would create a 5.1-kilometre (17,000 ft) impact crater.[19][4]

Expired 2036 path of risk

[edit]

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 deflection strategies.[106] 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.[107] 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.[108] 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 m) of roughly 1,000 kilometres (620 mi) for most of North America, Brazil and Africa, 3,000 km (1,900 mi) for Japan and 4,500 km (2,800 mi) for some areas in Hawaii.[109]

Exploration

[edit]

NASA

[edit]

OSIRIS-APEX post-Earth-encounter rendezvous

[edit]

The OSIRIS-REx spacecraft returned a sample of Bennu to Earth on 24 September 2023.[110] 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.[111][112] For its Apophis mission after the sample return, OSIRIS-REx was renamed OSIRIS-APEX (short for OSIRIS-Apophis Explorer).[113]

Planetary Society

[edit]

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 entries from 20 countries on 6 continents.[114]

The commercial competition was won by a design called Foresight created by SpaceWorks Engineering.[115][114][clarification needed] 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 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.[114][116]

ESA

[edit]

Don Quijote

[edit]

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.[117]

Ramses

[edit]

Apophis is the target of the European Space Agency's proposed Ramses (Rapid Apophis Mission for Security and Safety) mission, with a launch in 2026–2028[h] and rendezvous with the asteroid in 2029.[118][119]

Satis

[edit]

In parallel with Ramses, ESA is also considering a stand-alone CubeSat mission called Satis.[120]

CNSA

[edit]

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 1996 FG3 to conduct in situ sampling analysis on the surface.[121] The spacecraft launched on 28 May 2025, with a different set of targets.[122][123]

Proposed deflection strategies

[edit]
Further information: Asteroid impact avoidance

Studies by NASA, ESA,[124] and various research groups in addition to the Planetary Society contest teams,[125] have described a number of proposals for deflecting Apophis or similar objects, including gravitational tractor, kinetic impact, and nuclear bomb methods.

On 30 December 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.[126]

On 16 August 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.[127]

On 15 February 2016, Sabit Saitgarayev, of the Makeyev Rocket Design Bureau, announced intentions to use Russian ICBMs to target relatively small near-Earth objects. 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.[128]

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.[129]

[edit]

In Id Software's video game Rage, the backstory involves the asteroid colliding with Earth on 23 August 2029. The asteroid almost wipes out the human race and ushers in a post-apocalyptic age.[130][131]

In the grand strategy video game Terra Invicta, the player can mount a scientific expedition to Apophis when it flies close to Earth in 2029.[132]

In music, the asteroid Apophis is referred to in the song "The Profit of Doom" by gothic metal band Type O Negative on their 2007 album Dead Again. The lyrics refer to the asteroid 99942 Apophis, which at that time was considered to have a possibility of hitting Earth on Friday, April 13, 2029.[131]

See also

[edit]

Notes

[edit]
  1. ^ Like all orbital elements, the E-MOID changes depending on the epoch it is defined at. At epoch May 2025, the E-MOID is 0.000038 AU, but in early 2029 it will be around 0.00006 AU (ca 9000 km).[2]
  2. ^ Of the six asteroids with a higher Palermo scale rating than Apophis at the time:
  3. ^ This is normal for classical names in which the penultimate syllable is short.
  4. ^ The minimum possible Earth approach between April 5–20, 2116 is 0.00102 AU (153 thousand km). "JPL Horizons" gives 13 million km for 3σ[44]
  5. ^ "JPL Horizons" gives 42 million km for 3σ[45]
  6. ^ On 8 January 2022 Venus was even closer to Earth at 0.2658 AU (39.76 million km; 24.71 million mi; 103.4 LD).
  7. ^ Using the 9 March 2021 solution, JPL gave the strength of the Yarkovsky effect as , with an uncertainty of . The SNR, defined as the size of the signal divided by the uncertainty, is . As of the latest orbit solution (29 June 2021), the SNR is (again lower than Bennu's).
  8. ^ 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.

References

[edit]
  1. ^ a b c d e f g h i j k l m n o p q r s t u v w "JPL Small-Body Database Browser: 99942 Apophis (2004 MN4)" (last observation: 9 April 2022; arc: 18.07 years; JPL #220 solution date: 25 June 2024). Retrieved 28 February 2025.
  2. ^ a b c d e f Farnocchia, D.; Chesley, S. R.; Chodas, P. W.; Micheli, M. (20 February 2013). "Yarkovsky-driven impact risk analysis for asteroid (99942) Apophis". Icarus. 224 (1): 192. arXiv:1301.1607. Bibcode:2013Icar..224..192F. doi:10.1016/j.icarus.2013.02.020. S2CID 119088923.
  3. ^ a b c d e f g Brozović, M.; Benner, L. A. M.; McMichael, J. G.; Giorgini, J. D.; et al. (15 January 2018). "Goldstone and Arecibo radar observations of (99942) Apophis in 2012–2013" (PDF). Icarus. 300: 115–128. Bibcode:2018Icar..300..115B. doi:10.1016/j.icarus.2017.08.032. Retrieved 19 August 2018.
  4. ^ a b c d e f g h i j "99942 Apophis (2004 MN4) Earth Impact Risk Summary". NASA/JPL Center for NEO Studies. 6 May 2013. Archived from the original on 11 May 2013. See also updated version at "Sentry: Earth Impact Monitoring, Object Details". NASA/JPL Center for NEO Studies. Archived from the original on 8 February 2021. Retrieved 8 February 2021.
  5. ^ Binzel, R. P. (2007). "Can NEAs be Grouped by Their Common Physical Characteristics?" (PDF). Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology. aero.org. Archived from the original (PDF) on 12 April 2012.
  6. ^ a b c "99942 Apophis". The Near-Earth Asteroids Data Base at E.A.R.N. Archived from the original on 16 June 2012. Retrieved 15 October 2009.
  7. ^ a b c Reddy, Vishnu; Kelley, Michael S.; Dotson, Jessie; Farnocchia, Davide; et al. (31 May 2022). "Apophis Planetary Defense Campaign". The Planetary Science Journal. 3 (5): 123. Bibcode:2022PSJ.....3..123R. doi:10.3847/PSJ/ac66eb. hdl:10150/670423. S2CID 249227833.
  8. ^ a b c d e Pravec, P.; Scheirich, P.; Ďurech, J.; Pollock, J.; et al. (2014). "The tumbling spin state of (99942) Apophis" (PDF). Icarus. 233: 48–60. Bibcode:2014Icar..233...48P. doi:10.1016/j.icarus.2014.01.026. Archived from the original (PDF) on 5 March 2016. Retrieved 26 November 2014.
  9. ^ a b c d ESA (9 January 2013). "Herschel intercepts asteroid Apophis". European Space Agency (ESA). Retrieved 9 January 2013.
  10. ^ "99942 Apophis dynamical parameters". NEODyS-2. 14 March 2021. Retrieved 14 March 2021.
  11. ^ a b c d 13 April 2029 approach: 0.000254093 AU (38,011.8 km). 38012km "geocentric distance" – 6378km "Earth radius" = 31634km
  12. ^ a b David Noland (7 November 2006). "5 Plans to Head Off the Apophis Killer Asteroid". Popular Mechanics. Archived from the original on 12 June 2018. Retrieved 14 March 2021.
  13. ^ deGrasse Tyson, N. (12 March 2008). "Neil deGrasse Tyson — Death By Giant Meteor". Retrieved 14 March 2021 – via YouTube.
  14. ^ Giorgini, Jon; et al. (4 October 2007). "Predicting the Earth encounters of (99942) Apophis" (PDF). Icarus. 193: 1–19. doi:10.1016/j.icarus.2007.09.012. Archived from the original (PDF) on 22 December 2016.
  15. ^ a b c Yeomans, D.; Chesley, S.; Chodas, P. (23 December 2004). "Near-Earth Asteroid 2004 MN4 Reaches Highest Score To Date On Hazard Scale". NASA/JPL CNEOS. Retrieved 31 January 2024. 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.
  16. ^ a b c d e f Giorgini, J. (October 2007). "Predicting Apophis' Earth Encounters in 2029 and 2036". Archived from the original on 15 January 2016.
  17. ^ a b c d Jon Giorgini; et al. (4 October 2007). "Predicting the Earth encounters of (99942) Apophis" (PDF). Icarus. 193: 1–19. doi:10.1016/j.icarus.2007.09.012. Archived from the original (PDF) on 22 December 2016.
  18. ^ a b Marcus, R.; Melosh, H. J.; Collins, G. (2010). "Earth Impact Effects Program". Imperial College London / Purdue University. Retrieved 14 March 2021. (solution using 370 metres, 3000 kg/m3, 12.6 km/s, 45 degrees)
  19. ^ a b "NASA Rules Out Earth Impact in 2036 for Asteroid Apophis". NASA. 10 January 2013. Retrieved 10 January 2013.
  20. ^ Schilling, G. (27 October 2020). "The subtle effect of sunlight may turn the near-Earth asteroid Apophis toward Earth in 2068 . . . but chances for impact remain small". Sky & Telescope. Sky & Telescope. Retrieved 1 November 2020.
  21. ^ a b "Goldstone Radar Observations Planning: 99942 Apophis in 2021". Jet Propulsion Laboratory. 9 March 2021. Retrieved 19 March 2021.
  22. ^ "NASA Analysis: Earth Is Safe From Asteroid Apophis for 100-Plus Years". Jet Propulsion Laboratory. 25 March 2021.
  23. ^ Hurst, Luke (28 March 2021). "Asteroid Apophis won't hit Earth for at least 100 years, says NASA". euronews. Retrieved 2 April 2021.
  24. ^ a b c "Horizons Batch for Apophis @ 2029-Apr-13 21:45:03.628 showing 3-sigma uncertainty of ±3.3km". JPL Horizons. Archived from the original on 31 January 2022. Retrieved 28 February 2025.
  25. ^ "Sentry: Earth Impact Monitoring". NASA/JPL Center for NEO Studies. Archived from the original on 24 March 2021. Retrieved 3 March 2021. (Use Unconstrained Settings to reveal 1979 XB with impact probability below 1e-6)
  26. ^ Brown, D.; Wendel, J.; Agle, D. C. (29 April 2019). "Scientists Planning Now for Asteroid Flyby a Decade Away". NASA. Retrieved 29 April 2019.
  27. ^ "MPEC 2004-Y70 : 2004 MN4". IAU Minor Planet Center. 27 December 2004.
  28. ^ a b c Yeomans, D.; Chodas, P.; Chesley, S. (27 December 2004). "Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4". NASA/JPL CNEOS. Retrieved 31 January 2024.
  29. ^ a b c d "Scheduled Arecibo Radar Asteroid Observations". National Astronomy and Ionosphere Center.
  30. ^ a b Chodas, P.; Chesley, S.; Giorgini, J.; Yeomans, D. (3 February 2005). "Radar Observations Refine the Future Motion of Asteroid 2004 MN4". NASA's Near Earth Object Program Office. Retrieved 31 January 2024.
  31. ^ a b c d Cooke, B. (18 August 2005). "Asteroid Apophis set for a makeover". Astronomy Magazine. Retrieved 8 October 2009.{{cite journal}}: CS1 maint: deprecated archival service (link)
  32. ^ Hill, J. (2010). "Apep (Apophis)". Ancient Egypt Online. Retrieved 24 July 2021.
  33. ^ a b Phait, Phil (19 April 2021), "Apophis and Stargate", Bad Astronomy Newsletter, no. 315, retrieved 11 August 2025
  34. ^ "Apophis Facts". NASA. 28 March 2025. Retrieved 11 August 2025. Tholen said he and co-discoverer, the late Roy Tucker, were already familiar with the name Apophis because of the evil and powerful character by that name in the television series Stargate SG-1. He said it was "icing on the cake" that the name they selected was also a character in a popular TV show. But Tholen said that, contrary to some reports, the asteroid was not named for the TV character.
  35. ^ "Apophis". Dictionary.com Unabridged (Online). n.d.
  36. ^ As an example, here is David Tholen, the discoverer of the asteroid, pronouncing the name: "DPS 52 Monday Press Conference". AAS Press Office. 26 October 2020 – via YouTube.
  37. ^ Finlay, Alec; Sharples, Ray; Moskowitz, Denis (24 April 2008). One Hundred Year Star-Diary: 2008-2107. Platform Projects/Morning Star. ISBN 9780955202711. OCLC 316730683.
  38. ^ Finlay, Alec (2 April 2008). "Symbols for One Hundred Year Star-Diary". Kielder Observatory Astronomical Society. Archived from the original on 12 October 2008.
  39. ^ a b Reddy, V.; Sanchez, J. A.; Furfaro, R.; Binzel, R. P.; et al. (5 March 2018). "Surface Composition of (99942) Apophis". The Astronomical Journal. 155 (3). American Astronomical Society: 140. arXiv:1803.05375. Bibcode:2018AJ....155..140R. doi:10.3847/1538-3881/aaaa1c. ISSN 1538-3881. S2CID 78087061.
  40. ^ See "deldot" in this JPL Horizons simulation and this one.
  41. ^ "Horizons Batch for Apophis @ 2036-Mar-27 08:31 showing 3-sigma uncertainty of ±124566km". JPL Horizons. Archived from the original on 10 July 2023. Retrieved 28 February 2025.
  42. ^ "Horizons Batch for Apophis @ 2051-Apr-20 02:05 showing 3-sigma uncertainty of ±237314km". JPL Horizons. Retrieved 1 March 2025.
  43. ^ "Horizons Batch for Apophis @ 2116-Apr-12 21:44 showing 3-sigma uncertainty of ±13 million km". JPL Horizons. Retrieved 28 February 2025.
  44. ^ "Horizons Batch for Apophis @ 2117-Oct-07 17:21 showing 3-sigma uncertainty of ±42 million km". JPL Horizons. Retrieved 28 February 2025.
  45. ^ "OSIRIS-REx Spacecraft Departs for New Mission". 24 September 2023.
  46. ^ "List of satellites in geostationary orbit". satsig.net.
  47. ^ Byrd, D. (30 April 2019). "Preparing for asteroid Apophis | EarthSky.org". earthsky.org. Retrieved 1 May 2019.
  48. ^ a b "(99942) Apophis Ephemerides for 13 Apr 2029". NEODyS (Near Earth Objects — Dynamic Site). Retrieved 19 August 2018.
  49. ^ "The astronomical magnitude scale". International Comet Quarterly. Retrieved 19 January 2021.
  50. ^ From ecliptic longitude and latitude of 221°, −16° to 16°, 12° (according to this Horizons run), or in right ascension and declination, from 14h14m, −30°17' to 0h39m, 16°51' (using 29' this and this).
  51. ^ According to this JPL Horizons run.
  52. ^ a b c "Horizons Batch for Apophis Orbital Elements for 2029-01-01 and 2030-01-01". JPL Horizons. Retrieved 31 July 2022.
  53. ^ "Neptune from the VLT with and without adaptive optics". ESO. 18 July 2018. Retrieved 17 October 2022.
  54. ^ a b Marchis, F.; et al. "Multiple asteroid systems: Dimensions and thermal properties from Spitzer Space Telescope and ground-based observations". Icarus. 221 (2): 1130–1161. Bibcode:2012Icar..221.1130M. doi:10.1016/j.icarus.2012.09.013. Retrieved 24 August 2018.
  55. ^ "Venus 2036-May-30 @ JPL Horizons".
  56. ^ "Horizons Batch for Apophis on 2068-Apr-12". JPL Horizons. Retrieved 2 March 2025.
  57. ^ "99942 Apophis Ephemerides for April 2068". NEODyS (Near Earth Objects — Dynamic Site). Archived from the original on 10 March 2021. Retrieved 9 May 2019.
  58. ^ a b c "NEODyS : (99942) Apophis (Close Approaches)". NEODyS (Near Earth Objects—Dynamic Site). Retrieved 14 March 2021.
  59. ^ Brown, D. (7 October 2009). "NASA Refines Asteroid Apophis' Path Toward Earth". NASA's Near Earth Object Program Office. Retrieved 31 January 2024.
  60. ^ a b Fischer, D. (27 December 2004). "2004 MN4 Earth Impact Risk Summary (computed on Dec 27, 2004)". The Cosmic Mirror. Archived from the original on 14 March 2005. Retrieved 4 November 2011.
  61. ^ a b Virtual Impactor for 13 April 2029 (Stretch LOV = 1.29E+1) * Earth radius of 6,420 km = 82,818 km.
  62. ^ a b c "99942 Apophis (2004 MN4) Earth Impact Risk Summary". NASA/JPL. 5 August 2006. Archived from the original on 5 August 2006. Retrieved 13 January 2013.
  63. ^ Morrison, D. (22 July 2005). "Schweickart Proposes Study of Impact Risk from Apophis (MN4)". NASA. Archived from the original on 29 September 2009. Retrieved 8 October 2009.
  64. ^ "Hawaii astronomers keep tabs on asteroid Apophis". Astronomy Magazine. 10 March 2011. Retrieved 10 March 2011.
  65. ^ Morrison, D. (6 April 2011). "Asteroid 2004 MN4 will come scarily close to Earth on April 13, 2029, but it will not hit". Science@NASA.
  66. ^ Vergano, D. (10 November 2010). "Apophis asteroid encounter in 2013 should help answer impact worries". USA Today ScienceFair. Retrieved 10 November 2010.
  67. ^ "99942 Apophis Ephemerides for 9 Jan 2013". NEODyS (Near Earth Objects — Dynamic Site). Retrieved 14 March 2021.
  68. ^ a b Benner, L. A. M. (9 January 2013). "99942 Apophis 2013 Goldstone Radar Observations Planning". NASA/JPL Asteroid Radar Research. Retrieved 9 January 2013.
  69. ^ "Apophis Risk Assessment Updated". cneos.jpl.nasa.gov. 21 February 2013. Archived from the original on 8 April 2019.
  70. ^ "Update notes: Apophis (Mar 2015)". Sentry: Earth Impact Monitoring, Operational Notes. NASA/JPL Center for NEO Studies. 2 March 2015. Archived from the original on 14 April 2017. Retrieved 8 May 2019.
  71. ^ "(99942) Apophis Orbit". IAU Minor Planet Center. Retrieved 1 April 2021.
  72. ^ a b Tholen, D.; Farnocchia, D. (October 2020). "Detection of Yarkovsky Acceleration of (99942) Apophis". Bulletin of the American Astronomical Society. 52 (6): 214.06. Bibcode:2020DPS....5221406T.
  73. ^ a b Jorge A. Pérez-Hernández & Luis Benet (11 January 2022). "Non-zero Yarkovsky acceleration for near-Earth asteroid (99942) Apophis". Nature Communications Earth & Environment. 3 (1) 10. Bibcode:2022ComEE...3...10P. doi:10.1038/s43247-021-00337-x.
  74. ^ Satpathy, Akash; Mainzer, Amy; Masiero, Joseph R.; Linder, Tyler; et al. (31 May 2022). "NEOWISE Observations of the Potentially Hazardous Asteroid (99942) Apophis". The Planetary Science Journal. 3 (5): 124. arXiv:2204.05412. Bibcode:2022PSJ.....3..124S. doi:10.3847/PSJ/ac66d1. S2CID 248118987.
  75. ^ Banner, T. (4 March 2021). ""Apophis": Gefährlicher Asteroid nähert sich der Erde – Letzte Chance für Forschende" ["Apophis": Hazardous asteroid approaches Earth – last chance for scientists]. Frankfurter Rundschau (in German). Retrieved 4 March 2021.
  76. ^ a b "C53-NEOSSat – Observations and residuals". NEODyS-2. Retrieved 4 March 2021.
  77. ^ Tony Greicius, ed. (31 May 2022). "Planetary Defense Exercise Uses Apophis as Hazardous Asteroid Stand-In". NASA. Retrieved 1 June 2022.
  78. ^ a b Removed Objects from Sentry Risk Table
  79. ^ a b c d e "Chasing the Shadow of (99942) Apophis" (PDF). Journal of Occultation Astronomy. 11 (3): 1–2, 24–29. 2021. Retrieved 27 November 2021.
  80. ^ a b c "Apophis' Yarkovsky acceleration improved through stellar occultation". Gaia Image of the Week. European Space Agency (ESA). 29 March 2021. Retrieved 27 November 2021.
  81. ^ a b Tanga, P. (10 March 2021). "Targeted Campaigns – Apophis 2021". Archived from the original on 12 March 2021. Retrieved 12 March 2021.
  82. ^ a b "Lifetime Achievement Award of the International Occultation Timing Association". asteroidoccultation.com. International Occultation Timing Association. 2021. Retrieved 27 November 2021.
  83. ^ Marchis, F. (10 March 2021). "We Got it! The Story of Astronomers and Citizen Astronomers Catching Hazardous Apophis Asteroid over Colorado and Louisiana". SETI Institute. Archived from the original on 10 March 2021. Retrieved 13 March 2021.
  84. ^ "Asteroidal Occultation Reviewed Results for North America – 2021 Asteroidal Occultation Preliminary Results". asteroidoccultation.com. 8 March 2021. Archived from the original on 14 March 2021. Retrieved 12 March 2021.
  85. ^ "Reports of Apophis occultation 2021 Mar. 7 for our stations 3 and 4 near Oakdale, Louisiana (SwRI lines A28 and A30)". Verenigung veer Sterrenkunde. 9 March 2021. Retrieved 13 March 2021. (requires registration)
  86. ^ "JPL Small-Body Database Browser: 99942 Apophis (2004 MN4)" (last observation: 8 March 2021; arc: 16.98 years; JPL #206 solution date: 9 March 2021). 9 March 2021. Archived from the original on 11 March 2021. Retrieved 11 March 2021.
  87. ^ Bamberger, D.; Wells, G. (September 2018). "Detection of the Yarkovsky Effect on 1998 SD9 from Optical Observations". Research Notes of the AAS. 2 (3): 164. Bibcode:2018RNAAS...2..164B. doi:10.3847/2515-5172/aadf80. S2CID 125805680.
  88. ^ "2004 MN4 Earth Impact Risk Summary". NASA/JPL. 5 February 2005. Archived from the original on 6 February 2005. Retrieved 13 January 2013.
  89. ^ "99942 Apophis Earth Impact Risk Summary". NASA JPL. 18 October 2005. Archived from the original on 18 October 2005. Retrieved 13 January 2013.
  90. ^ Wee, L. K.; Goh, G. H. (14 December 2012). "A geostationary Earth orbit satellite model using Easy Java Simulation". Physics Education. 48 (1). IOP Publishing: 72–79. arXiv:1212.3863. doi:10.1088/0031-9120/48/1/72. ISSN 0031-9120. S2CID 119208827.
  91. ^ "99942 Apophis (2004 MN4) Earth Impact Risk Summary". NASA/JPL. 1 July 2006. Archived from the original on 1 July 2006. Retrieved 13 January 2013.
  92. ^ a b Sauerbier, M. (4 April 2008). "Ich habe den Weltuntergang ausgerechnet!" [I have calculated the apocalypse]. Bild (in German). Archived from the original on 9 August 2018. Retrieved 14 March 2021.
  93. ^ "NASA refutes story of boy who predicted asteroid collision". CBC/Radio-Canada. 16 April 2008. Retrieved 8 November 2015.
  94. ^ "German schoolboy, 13, corrects NASA's asteroid figures". Archived from the original on 20 April 2008. Retrieved 16 April 2008.
  95. ^ Brown, D. (16 April 2008). "NASA Statement on Student Asteroid Calculations". NASA. Archived from the original on 1 May 2008.
  96. ^ "99942 Apophis (2004 MN4)". neo.jpl.nasa.gov. Archived from the original on 2 March 2017. Retrieved 9 August 2017.
  97. ^ Brown, D. (7 October 2009). "NASA Refines Asteroid Apophis' Path Toward Earth". Archived from the original on 9 October 2009. Retrieved 7 October 2009.
  98. ^ Giorgini, J. "Apophis Trajectory Change 2018–2036: Energy Reflection, Absorption, and Emission". NASA. Archived from the original on 9 November 2007.
  99. ^ "99942 Apophis (2004 MN4) Earth Impact Risk Summary". NASA/JPL. 6 May 2013. Archived from the original on 10 January 2013. Retrieved 13 March 2021.
  100. ^ a b c Kelly Beatty (9 January 2013). "Asteroid Apophis Takes a Pass in 2036". Sky & Telescope. Sky & Telescope. Retrieved 10 November 2014.
  101. ^ Phil Plait (10 January 2013). "Impact Threat from Near-Earth Asteroid Apophis in 2036 Now Ruled Out". Slate. Bad Astronomy blog. Retrieved 10 January 2013.
  102. ^ "99942 Apophis (2004 MN4) Earth Impact Risk Summary". NASA/JPL. 8 October 2014. Archived from the original on 23 March 2016.
  103. ^ "JPL Small-Body Database Browser". 6 November 2020. Archived from the original on 6 November 2020.
  104. ^ Baurov, Y.A.; Albanese, L.; Meneguzzo, F.; Menshikov, V.A. (2013). "Protecting the planet from the asteroid hazard". Int. J. Pure Appl. Phys. 9 (3): 151–168.
  105. ^ Schweickart, R. "Threat Characterization: Trajectory dynamics (White Paper 39)" (PDF). Figure 4, pp. 9. B612 Foundation. Archived from the original (PDF) on 28 February 2008. Retrieved 22 February 2008.
  106. ^ Donald B. Gennery (5–8 March 2007), "Range of Possible Impact Points on April 13, 2036" (PDF), Scenarios for Dealing with Apophis, presented at the Planetary Defense Conference, Washington, D.C., archived from the original (PDF) on 12 April 2012
  107. ^ Baileya, N. J. (2006). "Near Earth Object impact simulation tool for supporting the NEO mitigation decision making process". Near Earth Objects. 236: 477. Bibcode:2007IAUS..236..477B. doi:10.1017/S1743921307003614.
  108. ^ Paine, M. P. (January 1999). "The Threat is Out There" (PDF). Science of Tsunami Hazards. 17 (3): 155. Archived (PDF) from the original on 6 June 2015. Retrieved 14 March 2021.
  109. ^ OSIRIS-REx factsheet (PDF). Explorers and Heliophysics Projects Division. ehpd.gsfc.nasa.gov (Report). Goddard SFC: NASA. August 2011. Public Domain This article incorporates text from this source, which is in the public domain.
  110. ^ Bartels, M. (19 January 2021). "NASA's OSIRIS-REx probe could make a 2nd stop at infamous asteroid Apophis". Space.com. Retrieved 28 January 2021.
  111. ^ Lauretta, D. S.; Bierhaus, E. B.; Binzel, R. P.; Bos, B. J. (6 November 2020). OSIRIS-REx at Apophis: Opportunity for an Extended Mission (PDF). Apophis T–9 Years: Knowledge Opportunities for the Science of Planetary Defense.
  112. ^ Mace Kelley, Mikayla (25 April 2022). "NASA gives green light for OSIRIS-REx spacecraft to visit another asteroid". University of Arizona News. Retrieved 26 April 2022.
  113. ^ a b c Kaplan, Mat (26 February 2008). "Planetary Society Names Winners of $50,000 Asteroid Tagging Competition". www.planetary.org. Archived from the original on 12 August 2020.
  114. ^ Rincon, P. (26 February 2008). "US team wins asteroid competition". Retrieved 25 March 2009.
  115. ^ Sharma, Jonathan; Lafleur, Jarret; Shah, Nilesh; Apa, Jilian; Townley, Jonathan; Barron, Kreston (30 April 2007). "PHAROS: Shedding Light on the Near-Earth Asteroid Apophis" (PDF). ESMD Space Grant Systems Engineering Paper Competition. Georgia Institute of Technology. Archived (PDF) from the original on 15 November 2024.
  116. ^ "Don Quijote concept". esa.int. European Space Agency. 4 April 2006. Archived from the original on 4 September 2006.
  117. ^ Morelli, Andrea C.; Mannocchi, Alessandra; et al. (September 2023). "Initial Trajectory Assessment of the RAMSES Mission to (99942) Apophis". arXiv:2309.00435 [astro-ph.EP].
  118. ^ Bartels, Meghan (16 July 2024). "Europe Announces New Mission to Infamous Asteroid Apophis". Scientific American. Retrieved 28 October 2024.
  119. ^ Kulu, Erik. "Satis". Nanosats Database. Retrieved 25 September 2025.
  120. ^ Yu Fei (7 March 2017). "Riding an asteroid: China's next space goal". Xinhua News Agency. Retrieved 1 May 2017.
  121. ^ Jones, Andrew (26 June 2023). "China conducts parachute tests for asteroid sample return mission". SpaceNews. Retrieved 28 October 2024.
  122. ^ Clark, Stephen (28 May 2025). "China extends its reach into the Solar System with launch of asteroid mission". Ars Technica. New York: Conde Nast. Archived from the original on 29 May 2025. Retrieved 29 May 2025.
  123. ^ Izzo, D.; Bourdoux, A.; Walker, R.; Ongaro, F. (2006). "Optimal Trajectories for the Impulsive Deflection of NEOs" (PDF). Acta Astronautica. 59 (1–5): 294–300. Bibcode:2006AcAau..59..294I. doi:10.1016/j.actaastro.2006.02.002.
  124. ^ "Scenarios for Dealing with Apophis" (PDF). The Aerospace Corporation. Archived from the original (PDF) on 27 August 2008. Retrieved 18 July 2008.
  125. ^ Isachenkov, V. (30 December 2009). "Russia may send spacecraft to knock away asteroid". Yahoo News. Archived from the original on 2 January 2010. Retrieved 31 December 2009.
  126. ^ "China Reveals Solar Sail Plan To Prevent Apophis Hitting Earth in 2036". Technology Review Physics arXiv Blog. 18 August 2011. Archived from the original on 26 November 2011. Retrieved 14 March 2021.
  127. ^ Khoury, A. (15 February 2016). "Russia wants to target near-Earth objects with its ICBMs". TASS in foxnews.com. Retrieved 15 February 2016.
  128. ^ Verma, Pranshu (21 October 2022). "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". The Washington Post. Retrieved 22 October 2022.
  129. ^ Winegarner, T. (6 November 2019). "Rage Interview: We speak with id's Tim Willits about their new IP, Rage". Gamespot.
  130. ^ a b Cooper, Quentin (18 November 2014). "Apophis asteroid: Doomsday delayed... again". bbc.com. Retrieved 15 April 2025.
  131. ^ "Major Update: Terra Invicta Release Candidate 1". 17 November 2025. Retrieved 18 November 2025.
[edit]
Wikimedia Commons logo
Wikimedia Commons has media related to (99942) Apophis.

Risk assessment

NASA

Retrieved from "https://en.wikipedia.org/w/index.php?title=99942_Apophis&oldid=1353643554"