101955 Bennu

101955 Bennu

Radar image of 101955 Bennu (courtesy Arecibo Observatory and JPL)[1][2]
Discovery
Discovery date	11 September 1999
Designations
MPC designation	101955
Pronunciation	/bɛˈnuː/
Named after	Bennu
Alternative names	1999 RQ36
Minor planet category	Apollo
Orbital characteristics[3]
Epoch 1 January 2011 (JD 2455562.5)
Uncertainty parameter 0
Observation arc	13.36 yr (4880 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	1.20 yr (436.65 d)
Mean anomaly	101.7039°
Mean motion	0° 49^m 28.056^s / day
Inclination	6.0349°
Longitude of ascending node	2.0609°
Argument of perihelion	66.2231°
Earth MOID	0.0032228 AU (482,120 km)
Jupiter MOID	3.87795 AU (580.133 Gm)
Jupiter Tisserand parameter	5.525
Proper orbital elements[3][4]
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
Mean radius	246 ± 10 m[1]
Equatorial radius	275 ± 10 m[1]
Mass	6.0×10^10 kg[5] to 7.76×10^10 kg
Mean density	1.26 ± 0.070 g/cm^3
Rotation period	4.288 h (0.1787 d)
Sidereal rotation period	4.288 hours[3]
Geometric albedo	0.046[4]
Surface temp. min mean max Kelvin[6] 236 259 279 Fahrenheit -34.6 6.8 42.8 Celsius -37 -14 6
Spectral type	B[4]
Absolute magnitude (H)	20.9

101955 Bennu (provisional designation 1999 RQ₃₆)^[7] is an Apollo asteroid discovered by the LINEAR Project on September 11, 1999. It is the planned target of the OSIRIS-REx mission which is intended to return samples to Earth in 2023 for further study.^[8][9] It is a potential Earth impactor and is listed on the Sentry Risk Table with the third highest rating on the Palermo Technical Impact Hazard Scale.^[10]

101955 Bennu has a mean diameter of approximately 492 m (1,614 ft; 0.306 mi) and has been observed extensively with the Arecibo Observatory Planetary Radar and the Goldstone Deep Space Network.^[1][2][11]

Possible Earth impact

On average, an asteroid with a diameter of 500 m (1,600 ft; 0.31 mi) can be expected to impact Earth about every 130,000 years or so.^[12] A 2010 dynamical study by Andrea Milani and collaborators predicted a series of eight potential Earth impacts by Bennu between 2169 and 2199. The cumulative probability of impact is dependent on physical properties of Bennu that were poorly known at the time, but was not found to exceed 0.07% for all eight encounters.^[13] The authors recognized that an accurate assessment of 101955 Bennu's probability of Earth impact would require a detailed shape model and additional observations (either from the ground or from spacecraft visiting the object) to determine the magnitude and direction of the Yarkovsky effect.

After the publication of the shape model and astrometry based on radar observations obtained in 1999, 2005, and 2011,^[1] it was possible to estimate the Yarkovsky acceleration and to revise the impact assessment. The current (as of 2014) best estimate of the impact probability is a cumulative probability of 0.037% in the interval 2175 to 2196.^[14] This corresponds to a score on the Palermo scale of −1.70.

Spacecraft missions

101955 Bennu has been considered a few times as the target of spacecraft missions due to the low Δv required to reach it from Earth orbit.^[15] OSIRIS-REx mission of NASA's New Frontiers Program is planned to launch in 2016, reach 101955 Bennu in 2019 and return samples to Earth in 2023.^[9]

Name

Bennu was named by Michael Puzio, a third-grader from North Carolina, one of more than eight thousand students from dozens of countries around the world who entered a "Name That Asteroid!" contest run by the University of Arizona, The Planetary Society, and the LINEAR Project, according to The Planetary Report, June 2013. Its name refers to the Egyptian mythological bird Bennu, which Puzio thought the spacecraft, OSIRIS-REx, including its TAGSAM arm, resembled.^[16]

Gallery

• 

  Artist concept of OSIRIS-REx at asteroid Bennu.^[1]

• 

  Illustration of OSIRIS-REx collecting a sample from asteroid Bennu.

• 

  Sample return capsule from the Stardust mission.

• Play media

  Asteroid Bennu is thought to contain materials present when the Solar System was first formed.

1. ^ Brown, Dwayne; Neal-Jones, Nancy (January 15, 2014). "NASA RELEASE 14-017 - NASA Invites Public to Send Names on an Asteroid Mission and Beyond". NASA. Retrieved January 16, 2014.

See also

• List of asteroids targeted for spacecraft visitation
• (341843) 2008 EV5

References

1. Nolan, M. C.; Magri, C.; Howell, E. S.; Benner, L. A. M.; Giorgini, J. D.; Hergenrother, C. W.; Hudson, R. S.; Lauretta, D. S.; Margot, J. L.; Ostro, S. J.; Scheeres, D. J. (2013). "Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations". Icarus 226 (1): 629–640. Bibcode:2013Icar..226..629N. doi:10.1016/j.icarus.2013.05.028. ISSN 0019-1035.
2. "Goldstone Delay-Doppler Images of 1999 RQ36". Asteroid Radar Research. Jet Propulsion Laboratory.
3. "101955 Bennu". JPL Small-Body Database. Jet Propulsion Laboratory. SPK-ID: 101955. Retrieved 20 April 2016.
4. "(101955) Bennu". NEODyS. University of Pisa. Retrieved 1 December 2015.
5. "101955 1999 RQ36: Earth Impact Risk Summary". NASA. Jet Propulsion Laboratory. August 5, 2010. Retrieved 24 November 2013.
6. "Planetary Habitability Calculators". Planetary Habitability Laboratory. University of Puerto Rico at Arecibo. Retrieved 6 December 2015.
7. We have a winner! The OSIRIS-REx asteroid's name is: Bennu!
8. Brown, Dwayne; Neal-Jones, Nancy (March 31, 2015). "RELEASE 15-056 - NASA’s OSIRIS-REx Mission Passes Critical Milestone". NASA. Retrieved April 4, 2015.
9. "NASA to Launch New Science Mission to Asteroid in 2016". NASA. 25 May 2011. Retrieved 21 May 2013.
10. "Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 2014-03-26.
11. Hudson, R. S.; Ostro, S. J.; Benner, L. A. M. "Recent Delay-Doppler Radar Asteroid Modeling Results: 1999 RQ36 and Craters on Toutatis". Bulletin of the American Astronomical Society (American Astronomical Society) 32: 1001. Bibcode:2000DPS....32.0710H.
12. Robert Marcus; H. Jay Melosh & Gareth Collins (2010). "Earth Impact Effects Program". Imperial College London / Purdue University. Retrieved 2013-02-07. (solution using density of 2,600 kg/m^3, sped of 17km/s, and impact angle of 45 degrees)
13. Milani, Andrea; Chesley, Steven R.; Sansaturio, Maria Eugenia; Bernardi, Fabrizio; Valsecchi, Giovanni B.; Arratia, Oscar (2009). "Long term impact risk for (101955) 1999 RQ₃₆". Icarus 203 (2): 460–471. arXiv:0901.3631. Bibcode:2009Icar..203..460M. doi:10.1016/j.icarus.2009.05.029.
14. Chesley, Steven R.; Farnocchia, Davide; Nolan, Michael C.; Vokrouhlický, David; Chodas, Paul W.; Milani, Andrea; Spoto, Federica; Rozitis, Benjamin; Benner, Lance A.M.; Bottke, William F.; Busch, Michael W.; Emery, Joshua P.; Howell, Ellen S.; Lauretta, Dante S.; Margot, Jean-Luc; Taylor, Patrick A. (2014). "Orbit and bulk density of the OSIRIS-REx target Asteroid (101955) Bennu". Icarus 235: 5–22. arXiv:1402.5573. Bibcode:2014Icar..235....5C. doi:10.1016/j.icarus.2014.02.020. ISSN 0019-1035.
15. Near-Earth Asteroid Delta-V for Space Rendezvous
16. Nine-Year-Old Names Asteroid Target of NASA Mission in Competition Run By The Planetary Society

External links

• Earth Impact Risk Summary: 101955 1999 RQ36 (Years: 2169–2199) – JPL near-Earth object website
• Orbit parameters – NASA website
• Temperature History and Dynamical Evolution of (101955) 1999 RQ 36: A Potential Target for Sample Return from a Primitive Asteroid (2011 ApJ 728 L42)
• Physical Properties of OSIRIS-REx Target Asteroid (101955) 1999 RQ36 derived from Herschel, ESO-VISIR and Spitzer observations (arXiv:1210.5370 : 19 Oct 2012)
• The Design Reference Asteroid for the OSIRIS-REx Mission Target (101955) Bennu (arXiv:1409.4704 : 16 Sep 2014)
• 101955 Bennu at the JPL Small-Body Database

• Discovery · Orbit diagram · Orbital elements · Physical parameters