• Pajola, Maurizio
• Nolan, M. C.
• Rizk, B.
• Bennett, C. A.
• Ballouz, R. -L.
• Connolly, H. C.
• Asad, M. Al
• Daly, R. T.
• Molaro, J. L.
• Avdellidou, C.
• Jawin, E. R.
• Bottke, W. F.
• Trang, D.
• Michel, P.
• Delbo, M.
• Bierhaus, E. B.
• Lauretta, D. S.
• Walsh, K. J.
• Daly, M. G.
• Wolner, C. W. V.
• Golish, D. R.
• Asphaug, E.
• Dellagiustina, D. N.
• Barnouin, O. S.
• Schwartz, S. R.

Abstract

An asteroid's history is determined in large part by its strength against collisions with other objects<SUP>1,2</SUP> (impact strength). Laboratory experiments on centimetre-scale meteorites<SUP>3</SUP> have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale<SUP>4,5</SUP>. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples<SUP>6</SUP> and images of the asteroid (25143) Itokawa<SUP>7</SUP>. It has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. Here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) Bennu. We show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. We infer that Bennu's metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-Earth space. We conclude that this population of near-Earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. Our results indicate that Bennu has been dynamically decoupled from the main asteroid belt for 1.75 ± 0.75 million years....

Topics

• impedance spectroscopy
• surface
• experiment
• simulation
• strength