OSIRIS-REx's target asteroid, Bennu (also known as the Near-Earth Object (NEO 101955) 1999 RQ36, is an exciting—and accessible—celestial body. It is classified as a B-type asteroid, and considered to be a rare specimen. It has changed little since the time of its formation 4 billion years ago, and may reveal a wealth of information about the early Solar System.
Bennu takes about 1.2 years to orbit the Sun. It moves in an elliptical pattern between Venus and Mars, crossing paths with Earth's orbit every six years. Measuring about 500 metres in diameter, it is a rubble pile made up of leftover rocks and other material that remained after the terrestrial planets formed. When observed using telescopes, it is very dark and rich in carbon and may hold organic materials, water and other light elements.
Of the 500,000 or so catalogued asteroids and about 9000 Near-Earth Objects, Bennu is also one of the most potentially hazardous known to humanity, with a 1/2700 risk of colliding with Earth between the years 2175 and 2196. Understanding its orbit and composition will help provide more conclusive data on how and when it might impact Earth.
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