Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface
2019
Small, kilometre-sized near-Earth
asteroidsare expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main
asteroid beltwhere they originate, and thermal or tidal processes act on them once they become near-Earth
asteroids. Here we present early measurements of numerous large candidate
impact craterson near-Earth
asteroid(101955) Bennu by the
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-
RegolithExplorer) mission, which indicate a surface that is between 100 million and 1
billion yearsold, predating Bennu’s expected duration as a near-Earth
asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent
mass movement: clusters of boulders at topographic lows, a deficiency of small craters and
infillof large craters. The oldest features likely record events from Bennu’s time in the main
asteroid belt.
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