101955 Bennu 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 tied for the highest cumulative rating on the Palermo Technical Impact Hazard Scale. It has a cumulative 1-in-1,800 chance of impacting Earth between 2178 and 2290 with the greatest risk being on 24 September 2182. It is named after the Bennu, the ancient Egyptian mythological bird associated with the Sun, creation, and rebirth.

101955 Bennu has a mean diameter of 490 m (1,610 ft; 0.30 mi) and has been observed extensively with the Arecibo Observatory planetary radar and the Goldstone Deep Space Network. Bennu was the target of the OSIRIS-REx mission which is intended to return its samples to Earth in 2023 for further study. On 3 December 2018, the OSIRIS-REx spacecraft arrived at Bennu after a two-year journey. It orbited the asteroid and mapped out Bennu's surface in detail, seeking potential sample collection sites. Analysis of the orbits allowed calculation of Bennu's mass and its distribution.

On 18 June 2019, NASA announced that the OSIRIS-REx spacecraft had closed in and captured an image from a distance of 600 metres (2,000 ft) from Bennu's surface. In October 2020, OSIRIS-REx successfully touched down on the surface of Bennu, collected a sample using an extendable arm, secured the sample and prepared for a return trip to Earth. On 10 May 2021, OSIRIS-REx successfully completed its departure from the Bennu asteroid while still carrying the sample of the asteroid rubble.

Astrometric observations between 1999 and 2013 have demonstrated that 101955 Bennu is influenced by the Yarkovsky effect, causing the semimajor axis of its orbit to drift on average by 284±1.5 meters/year. Analysis of the gravitational and thermal effects has given a bulk density of ρ = 1190±13 kg/m3, which is only slightly denser than water. Therefore, the predicted macroporosity is 40±10%, suggesting the interior has a rubble pile structure or even hollows. The estimated mass is (7.329±0.009)×1010 kg.

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