Bennu Sample Reveals Water Flowed in Restricted Channels
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- Mehmet Yesiltas and his Stony Brook University team published deep nanoscale analysis of a Bennu sample in PNAS, identifying three distinct chemical domains separated at scales of just 20 nanometers — roughly the size of a single large molecule.
- NASA's OSIRIS-REx mission returned the sample to Earth in September 2023, only the third-ever asteroid sample recovered, from Bennu, a carbon-rich near-Earth object roughly 500 meters wide.
- The sample divides into three chemical domains: aliphatic-rich regions of open-chain hydrocarbons, carbonate-rich zones of calcium and magnesium minerals, and nitrogen-bearing organic-rich regions hosting complex molecules likely inherited from older material or modified by fluid-rock interactions.
- Organosulfur compounds are found almost entirely in carbonate-rich regions, indicating those minerals precipitated from water-rich fluids while aliphatic and nitrogen-bearing organic regions remained dry enough to preserve fragile compounds.
- The sharp separation between altered and preserved domains shows water flowed through Bennu along restricted pathways during its early evolution, channeling hydrothermal activity rather than soaking the body uniformly.
- Researchers plan to compare the Bennu findings with samples from asteroid Ryugu returned by Japan's Hayabusa2 mission, aiming to reconstruct early solar system history and the origins of Earth in greater detail.
Why it matters: This is the deepest nanoscale look yet at asteroid Bennu's chemistry, and it shows the asteroid's water didn't percolate uniformly but moved through narrow channels, selectively altering some regions while leaving organics in others untouched. The planned Bennu-Ryugu sample comparison aims to produce a clearer picture of how the early solar system's water and prebiotic organics were distributed.
