99942 Apophis
 |
|
| Discovery | |
|---|---|
| Discovered by |
Roy A. Tucker David J. Tholen Fabrizio Bernardi |
| Discovery site | Kitt Peak |
| Discovery date | 19 June 2004 |
| Designations | |
|
Named after
|
Apep |
| 2004 MN4 | |
Aten  NEO, PHA |
|
| Orbital characteristics | |
| Epoch 7 December 2007 (JD 2454441.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 3635 days (9.95 yr) |
| Aphelion | 1.09851 AU (164.335 Gm) |
| Perihelion | 0.74605 AU (111.607 Gm) |
| 0.92228 AU (137.971 Gm) | |
| Eccentricity | 0.19108 |
| 0.89 yr (323.5 d) | |
|
Average orbital speed
|
30.728 km/s |
| 215.53998° | |
| 1.11278°/day | |
| Inclination | 3.33129° |
| 204.45719° | |
| 126.39364° | |
| Earth MOID | 0.000659446 AU (98,651.7 km) |
| Jupiter MOID | 4.12656 AU (617.325 Gm) |
| Jupiter Tisserand parameter | 6.467 |
| Physical characteristics | |
| Dimensions | 325±15 m |
|
Mean radius
|
0.1625 ± 0.0075 km |
| Mass | 4×1010 kg (assumed) |
|
Mean density
|
~3.2 g/cm3 |
|
Equatorial surface gravity
|
0.00027 m/s2 (average) |
|
Equatorial escape velocity
|
~0.52 km/h |
| 30.4 h (1.27 d) tumbling: precession period: 27.38±0.07 h rotation period: 263±6 h period of harmonic with strongest lightcurve amplitude: 30.56±0.01 h |
|
| 0.23 | |
| Temperature | 270 K |
| Sq | |
| 19.7 ± 0.4 | |
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 probability of up to 2.7% that it would hit Earth on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However, until 2006, a possibility remained that during the 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole, a small region no more than about 965 kilometres (600 miles) wide, that would 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. 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 on the Torino scale, reaching level 4.
The diameter of Apophis is, as of the most recent 2013 observations, approximately 325 metres (1,066 ft). 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 probability of an impact on April 13, 2036 had been eliminated. As of October 8, 2014, using observations through February 26, 2014, the odds of an impact on April 12, 2068, as calculated by the JPL Sentry risk table is 1 in 149,000. As of December 2016[update], of objects not recently observed, there were about five asteroids with a more notable Palermo Technical Impact Hazard Scale than Apophis. On average, an asteroid the size of Apophis (325 metres) can be expected to impact Earth about every 80,000 years.
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