Bennu
A dark, rubble-pile near-Earth asteroid about half a kilometre across, sampled by NASA's OSIRIS-REx mission.
Bennu (asteroid 101955) was discovered in 1999. About 490 metres wide and shaped roughly like a spinning top, it is a loosely bound rubble pile with a bulk density only a little above that of water. NASA's OSIRIS-REx spacecraft arrived in December 2018 and found a surface far rougher than expected, covered in boulders. It also saw small pebbles being thrown off the surface. In October 2020 the spacecraft briefly touched down and collected material; the sample capsule landed in Utah on 24 September 2023, carrying about 121.6 grams.
Laboratory studies show Bennu is rich in water-bearing clay minerals, carbonates, magnetite and organic matter, similar to CI and some CM chondrites but not an exact match to any known meteorite. Researchers have reported amino acids, all five nucleobases used in DNA and RNA, and salts left behind by evaporating brines.
Bennu also matters for planetary defence. Precise tracking showed its orbit drifts because of the Yarkovsky effect, and there is a very small chance, about 1 in 2,700 in total, that it could hit Earth before the year 2300, with 2182 the riskiest date. Its closest meteorite comparisons are CI chondrites like Orgueil and Ivuna.
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