Asteroid Bennu

(101955) Bennu is a small, carbon-rich near-Earth asteroid. Spacecraft observations indicate that it is a rubble-pile body: a loose aggregate of fragments, rather than a single solid block. Its composition and orbit made it a valuable target for studying primitive Solar System material and for assessing asteroid trajectories.

NASA's OSIRIS-REx spacecraft launched in 2016, reached Bennu in 2018, and collected surface material with a brief touch-and-go maneuver in October 2020. The return capsule landed in Utah on 24 September 2023. NASA reported a returned sample mass of 121.6 grams, more than twice the mission's minimum requirement. Because the material was collected in space and carefully curated after return, scientists could examine it while limiting some kinds of terrestrial contamination and alteration.

Laboratory analysis of Bennu material identified a varied suite of salt minerals, including sodium-rich carbonates, sulfates, chlorides and fluorides. Researchers interpret their sequence and associations as evidence that brines once evaporated in Bennu's parent body, an older body from which the present rubble-pile asteroid formed. Such minerals record water-rock chemistry; they do not imply that liquid water currently exists on Bennu. Some hydrated salts can change when exposed to Earth's atmosphere, making sample handling important.

A separate analysis reported amino acids—including 14 of the 20 used by terrestrial life to build proteins—and all five nucleobases found in DNA and RNA, along with ammonia and other organic molecules. These are chemical ingredients associated with life on Earth, not organisms or proof of biology. The findings help researchers investigate how organic compounds and water-altered environments developed in the early Solar System and whether asteroids could have delivered some prebiotic materials to young planets.

The sample provides direct evidence of Bennu's material, but scientists infer aspects of the ancient parent body's setting from mineral and chemical records. The exact paths by which these substances formed, and whether they ever progressed toward living systems, remain open research questions. Continued study of returned material and comparison with samples from other asteroids can refine those interpretations.