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Discovery[2]
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| Discovered by | Roy A. Tucker David J. Tholen Fabrizio Bernardi |
| Discovery site | Kitt Peak[1] |
| Discovery date | June 19, 2004 |
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Designations
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| Named after | Apep |
| Alternate name(s) | 2004 MN4 |
| Minor planet category |
Aten[2] |
| Epoch January 4, 2010 (JD 2455200.5) (Uncertainty=0)[2] |
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| Aphelion | 1.0987 AU |
| Perihelion | 0.74604 AU |
| Semi-major axis | 0.92241 AU |
| Eccentricity | 0.19121 |
| Orbital period | 323.58 d (0.89 a) |
| Average orbital speed | 30.728 km/s |
| Mean anomaly | 339.94° |
| Inclination | 3.3315° |
| Longitude of ascending node | 204.43° |
| Argument of perihelion | 126.42° |
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Physical characteristics
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| Dimensions | ~270 m[2] |
| Mass | 2.7×1010 kg (assumed)[3] |
| Mean density | ? g/cm³ |
| Equatorial surface gravity | ? |
| Escape velocity | ~0.52 km/h[4] |
| Rotation period | 30.4 h[2][5] |
| Albedo | 0.33 [2][5] |
| Temperature | 270 K |
| Spectral type | Sq [5] |
| Absolute magnitude (H) | 19.7 [2][5] |
99942 Apophis ( /əˈpɒfɪs/, previously known by its provisional designation 2004 MN4) is a near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a small probability (up to 2.7%) that it would strike the Earth in 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However, a possibility remained that during the 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole, a precise region in space no more than about a half-mile wide,[6] that would set up a future impact on April 13, 2036. This possibility kept the asteroid at Level 1 on the Torino impact hazard scale until August 2006, when the probability that Apophis will pass through the keyhole was determined to be very small. Apophis broke the record for the highest level on the Torino Scale, being, for only a short time, a level 4, before it was lowered.[7] Its diameter is approximately 270 meters (885 ft).[2] As of October 7, 2009[update], the probability of an April 13, 2036 impact is considered to be 1 in 250,000.[3][8] Of objects not recently observed, there are 7 asteroids with a more notable Palermo Technical Impact Hazard Scale than Apophis.[9]
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Based upon the observed brightness, Apophis' 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).
During the 2029 approach, Apophis’ brightness will peak at magnitude 3.4,[10] with a maximum angular speed of 42° per hour. The maximum apparent angular diameter will be ~2 arcseconds, so that it will be barely resolved by telescopes not equipped with adaptive optics.
Apophis was discovered on June 19, 2004, by Roy A. Tucker, David J. Tholen and Fabrizio Bernardi and the Kitt Peak National Observatory.[1] Precovery observations from March 15, 2004, were identified on December 27, and an improved orbit was computed.[11] Radar astrometry further refined the orbit.
When first discovered, the object received the provisional designation 2004 MN4 (sometimes written 2004 MN4), and news and scientific articles about it referred to it by that name. When 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, and it received the name "Apophis" on July 19, 2005. Apophis is the Greek name of the Ancient Egyptian enemy of Ra: Apep, the Uncreator, an evil serpent that dwells in the eternal darkness of the Duat (earth's middle) 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. Tholen and Tucker — two of the co-discoverers of the asteroid — are reportedly fans of the TV series Stargate SG-1. One of the show's persistent villains is an alien named Apophis who, on the show, gave rise to the myth of the Egyptian god.[12]
After the Minor Planet Center confirmed the June discovery of Apophis, an April 13, 2029 close approach was flagged by NASA's automatic Sentry system and NEODyS, a similar automatic program run by the University of Pisa and the University of Valladolid. On that date, it will become as bright as magnitude 3.4[10] (visible to the naked eye from rural as well as darker suburban areas, visible with binoculars from most locations[13]). This close approach will be visible from Europe, Africa, and western Asia. As a result of its close passage, it will move from the Aten to the Apollo class.
After Sentry and NEODyS announced the possible impact, additional observations decreased the uncertainty in Apophis' trajectory. As they did, the probability of an impact event temporarily climbed, peaking at 2.7% (1 in 37). Combined with its size, this caused Apophis to be assessed at level 4 on the Torino Scale and 1.10 on the Palermo Technical Impact Hazard Scale, scales scientists use to represent the danger of an asteroid hitting Earth. These are the highest values for which any object has been rated on either scale. It has since been downgraded to level 0 on the Torino Scale for both the 2029 and 2036 passes.[3] With a cumulative Palermo Scale rating of -2.9,[3] the risk of impact from Apophis is less than the background hazard level.[3]
On Friday, April 13, 2029, Apophis will pass Earth within the orbits of geosynchronous communication satellites.[14] It will return for another close Earth approach in 2036.
The 2029 pass will actually be much closer than the first predictions, but the uncertainty is such that an impact is ruled out. Similarly, the pass on April 13, 2036, carries little risk of an impact.
The close approach in 2029 will substantially alter the object's orbit, making predictions uncertain without more data. "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." said Jon Giorgini of JPL.[15] Apophis will pass within 0.0966 AU (14,450,000 km; 8,980,000 mi) of the Earth in 2013, allowing astronomers to refine the trajectory for future close passes.[16][17] Just after the close approach on 9 January 2013,[16] the asteroid should peak at about apparent magnitude 15.7,[18] On January 31, 2011, astronomers took the first new images of Apophis in more than 3 years.[19]
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 asked for an investigation of the necessity of placing a transponder on the asteroid for more accurate tracking of how its orbit is affected by the Yarkovsky effect.[20]
NASA initially estimated the energy that Apophis would have released if it struck Earth as the equivalent of 1480 megatons of TNT. A later, more refined NASA estimate was 880 megatons, then revised to 510 megatons.[3] The impacts which created the Barringer Crater or the Tunguska event are estimated to be in the 3–10 megaton range.[25] The 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons and the biggest hydrogen bomb ever exploded, the Tsar Bomba, was around 50 megatons. In comparison, the Chicxulub impact, believed by many to be a significant factor in the extinction of 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 kilometers, but would be unlikely to have long-lasting global effects, such as the initiation of an impact winter.
The B612 Foundation made estimates of Apophis' path if a 2036 Earth impact were to occur, as part of an effort to develop viable deflection strategies.[26] The result is a narrow corridor a few kilometers 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.[27][28] Using the computer simulation tool NEOSim, it was estimated that the hypothetical impact of Apophis in countries such as Colombia and Venezuela, which are in the path of risk, could have more than 10 million casualties.[29] An impact in the Atlantic or Pacific oceans would produce a devastating tsunami.[30]
In 2008, The Planetary Society, a California-based space advocacy group, organized a $50,000 competition to design an unmanned 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.[31] SpaceWorks proposed a simple orbiter with only two instruments and a radio beacon at a cost of ~140 million USD, launched aboard a Minotaur IV 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 imager for one month. It would then leave orbit and fly in formation with Apophis around the Sun at a range of two kilometers (1.2 miles). 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. Accelerometers 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, Spain, in cooperation with EADS Astrium, Friedrichshafen, Germany; University of Stuttgart, Germany; and Università di Pisa, Italy. Juan L. Cano was Principal Investigator.
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, UK; Rheinisches Institut für Umweltforschung, Germany; Royal Observatory of Belgium; and Telespazio, Italy. The Principal Investigator was Paolo D'Arrigo.
Two teams tied for second place in the Student Category: Monash University, Clayton Campus, Australia, with Dilani Kahawala as Principal Investigator; and University of Michigan, 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, under the leadership of Peter Weiss, received an honorable mention and $1,000 for the most innovative student proposal.
Apophis is one of two asteroids under consideration by the European Space Agency as the target of its Don Quijote mission to study the effects of impacting an asteroid.[32]
Studies by NASA, ESA,[33] and various research groups in addition to the Planetary Society contest teams,[34] 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, 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.[35]
On August 16, 2011, researchers at China's Tsinghua University proposed a 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. [36]
Risk assessment
NASA
| Preceded by (153814) 2001 WN5 |
Large NEO Earth close approach (inside the orbit of the moon) April 13, 2029 |
Succeeded by 2011 AG5 |
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