101955 Bennu

is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on September 11, 1999.

It is a potentially hazardous object that is listed on the Sentry Risk Table with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale. It has a cumulative 1-in-2,700 chance of impacting Earth between 2175–2199.

Physical description

Asteroid Bennu has a roughly spheroidal shape, which resembles a spinning top. The direction of rotation about its axis is retrograde with respect to its orbit. Bennu has a fairly smooth shape with one prominent 10–20 m boulder on its surface, in the southern hemisphere.

There is a well-defined ridge along the equator of asteroid Bennu. The presence of this ridge suggests that fine-grained regolith particles have accumulated in this area, possibly because of its low gravity and fast rotation.

Origin and evolution

The carbonaceous material that composes asteroid Bennu originally came from dying stars such as red giants and supernovae. According to the accretion theory, this material came together 4.5 billion years ago during the formation of the Solar System.

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.[24] 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 0.071% for all eight encounters.

”NASA should start thinking about this planet. “

— Wally Schirra

September

2060

Bennu will pass 0.005 AU (750,000 km; 460,000 mi) from Earth on 23 September 2060. The close approach of 2060 causes divergence in the close approach of 2135. On 25 September 2135 the nominal approach distance is 0.002 AU (300,000 km; 190,000 mi) from Earth, but Bennu could pass as close as 0.0007 AU (100,000 km; 65,000 mi).

September 2060

OSIRIS-REx

The OSIRIS-REx mission of NASA's New Frontiers Program was launched towards 101955 Bennu on September 8, 2016. It is expected to reach the asteroid in August 2018 and return samples to Earth in 2023.

OSIRIS-REx

Bennu

Name

The name Bennu was selected from more than eight thousand student entries 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.