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101955 Bennu
(provisional designation )〔(We have a winner! The OSIRIS-REx asteroid's name is: Bennu! )〕 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 for further study.〔 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.〔
has a mean diameter of approximately and has been observed extensively with the Arecibo Observatory Planetary Radar and the Goldstone Deep Space Network.〔〔〔
== Possible Earth impact ==
On average, an asteroid with a diameter of can be expected to impact Earth about every 130,000 years or so.〔 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.〔 The authors recognized that an accurate assessment of '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,〔 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.〔 This corresponds to a score on the Palermo scale of −1.70.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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