Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where 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 craters on near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, 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 infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.
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Raw through to calibrated datasets will be available via the Planetary Data System (PDS) (https://sbn.psi.edu/pds/resource/orex/). Data are delivered to the PDS according to the OSIRIS-REx Data Management Plan available in the OSIRIS-REx PDS archive. Higher-level products, for example, global mosaics and elevation maps, will be available in the PDS one year after departure from the asteroid.
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This material is based on work supported by NASA under contracts NNM10AA11C and NNH09ZDA007O issued through the New Frontiers Program. M.P. was supported for this research by the Italian Space Agency (ASI) under the ASI-INAF agreement no. 2017–37-H.0. M.D., P.M., and A.R. would like to acknowledge the French space agency CNES. M.D., A.R., P.M. and S.R.S acknowledge support from the Academies of Excellence on Complex Systems and Space, Environment, Risk and Resilience of the Initiative d’EXcellence ‘Joint, Excellent, and Dynamic Initiative’ (IDEX JEDI) of the Université Côte d’Azur. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
The authors declare no competing interests.
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Walsh, K.J., Jawin, E.R., Ballouz, RL. et al. Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface. Nat. Geosci. 12, 242–246 (2019). https://doi.org/10.1038/s41561-019-0326-6
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