Walsh, K. J., Jawin, Erica R., Ballouz, R. L., Barnouin, O. S., Bierhaus, E. B., Connolly, H. C., Jr., Molaro, J. L., McCoy, Timothy J., Delbo', M., Hartzell, C. M., Pajola, M., Schwartz, S. R., Trang, D., Asphaug, E., Becker, K. J., Beddingfield, C. B., Bennett, C. A., Bottke, W. F., Burke, K. N., Clark, B. C., Daly, M. G., DellaGiustina, D. N., Dworkin, J. P., Elder, C. M., Golish, D. R. et al. 2019. "Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface." Nature Geoscience, 12, (4) 242–246. https://doi.org/10.1038/s41561-019-0326-6.
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.
