101955 Bennu
101955 Bennu (provisional designation 1999 RQ36) 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 cumulative rating on the Palermo Technical Impact Hazard Scale. It has a cumulative 1-in-1,750 chance of impacting Earth between 2178 and 2290 with the greatest risk being on 24 September 2182. It is named after Bennu, the ancient Egyptian mythological bird associated with the Sun, creation, and rebirth.
Mosaic image of Bennu after two years of observation by OSIRIS-REx | |||||||||||||||||
| Discovery | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Discovered by | LINEAR | ||||||||||||||||
| Discovery site | Lincoln Lab's ETS | ||||||||||||||||
| Discovery date | 11 September 1999 | ||||||||||||||||
| Designations | |||||||||||||||||
MPC designation | (101955) Bennu | ||||||||||||||||
| Pronunciation | /ˈbɛnuː/ | ||||||||||||||||
Named after | Bennu | ||||||||||||||||
Alternative designations | 1999 RQ36 | ||||||||||||||||
Minor planet category | Apollo · NEO · PHA · risk listed | ||||||||||||||||
| Orbital characteristics | |||||||||||||||||
| Epoch 1 January 2011 (JD 2455562.5 ) | |||||||||||||||||
| Uncertainty parameter 0 | |||||||||||||||||
| Observation arc | 21.06 yr (7693 days) | ||||||||||||||||
| Aphelion | 1.3559 au (202.84 Gm) | ||||||||||||||||
| Perihelion | 0.89689 au (134.173 Gm) | ||||||||||||||||
Semi-major axis | 1.1264 au (168.51 Gm) | ||||||||||||||||
| Eccentricity | 0.20375 | ||||||||||||||||
Orbital period (sidereal) | 1.1955 yr (436.65 d) | ||||||||||||||||
Average orbital speed | 28.0 km/s (63,000 mph) | ||||||||||||||||
Mean anomaly | 101.7039° | ||||||||||||||||
Mean motion | 0° 49m 28.056s / day | ||||||||||||||||
| Inclination | 6.0349° | ||||||||||||||||
Longitude of ascending node | 2.0609° | ||||||||||||||||
| 66.2231° | |||||||||||||||||
| Earth MOID | 0.0032228 au (482,120 km) | ||||||||||||||||
| Venus MOID | 0.194 au (29,000,000 km) | ||||||||||||||||
| Mars MOID | 0.168 au (25,100,000 km) | ||||||||||||||||
| Jupiter MOID | 3.877 au (580.0 Gm) | ||||||||||||||||
| TJupiter | 5.525 | ||||||||||||||||
| Proper orbital elements | |||||||||||||||||
Proper eccentricity | 0.21145 | ||||||||||||||||
Proper inclination | 5.0415° | ||||||||||||||||
Proper mean motion | 301.1345 deg / yr | ||||||||||||||||
Proper orbital period | 1.19548 yr (436.649 d) | ||||||||||||||||
| Physical characteristics | |||||||||||||||||
| Dimensions | 565 m × 535 m × 508 m (1854 ft × 1755 ft × 1667 ft) | ||||||||||||||||
Mean radius | 245.03±0.08 m (804±0.262 ft) | ||||||||||||||||
Equatorial radius | 282.37±0.06 m (926.4±0.197 ft) | ||||||||||||||||
Polar radius | 249.25±0.06 m (817.74±0.197 ft) | ||||||||||||||||
Surface area | 0.782±0.004 km2 (0.302±0.002 sq mi) | ||||||||||||||||
| Volume | 0.0615±0.0001 km3 | ||||||||||||||||
| Mass | (7.329±0.009)×1010 kg | ||||||||||||||||
Mean density | 1.190±0.013 g/cm3 | ||||||||||||||||
Equatorial surface gravity | 6.27 micro-g | ||||||||||||||||
Synodic rotation period | 4.296057±0.000002 h | ||||||||||||||||
| 177.6±0.11° | |||||||||||||||||
North pole right ascension | +85.65±0.12° | ||||||||||||||||
North pole declination | −60.17±0.09° | ||||||||||||||||
| 0.044±0.002 | |||||||||||||||||
| |||||||||||||||||
| B F | |||||||||||||||||
| 20.9 | |||||||||||||||||
101955 Bennu has a mean diameter of 490 m (1,610 ft; 0.30 mi) and has been observed extensively by the Arecibo Observatory planetary radar and the Goldstone Deep Space Network.
Bennu was the target of the OSIRIS-REx mission that returned samples of the asteroid to Earth. The spacecraft, launched in September 2016, arrived at the asteroid two years later and mapped its surface in detail, seeking potential sample collection sites. Analysis of the orbits allowed calculation of Bennu's mass and its distribution. In October 2020, OSIRIS-REx briefly touched down and collected a sample of the asteroid's surface. A capsule containing the sample was returned and landed on Earth in September 2023, with distribution and analysis of the sample ongoing.