@article{c5595e914ea8445587b57badda3c2681,
title = "Bennu{\textquoteright}s near-Earth lifetime of 1.75 million years inferred from craters on its boulders",
abstract = "An asteroid{\textquoteright}s history is determined in large part by its strength against collisions with other objects1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples6 and images of the asteroid (25143) Itokawa7. 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{\textquoteright}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.",
author = "Ballouz, {R. L.} and Walsh, {K. J.} and Barnouin, {O. S.} and DellaGiustina, {D. N.} and Asad, {M. Al} and Jawin, {E. R.} and Daly, {M. G.} and Bottke, {W. F.} and P. Michel and C. Avdellidou and M. Delbo and Daly, {R. T.} and E. Asphaug and Bennett, {C. A.} and Bierhaus, {E. B.} and Connolly, {H. C.} and Golish, {D. R.} and Molaro, {J. L.} and Nolan, {M. C.} and M. Pajola and B. Rizk and Schwartz, {S. R.} and D. Trang and Wolner, {C. W.V.} and Lauretta, {D. S.}",
note = "Funding Information: Acknowledgements We thank D. P. Hamilton, K. A. Holsapple and P. Pravec for insights and feedback. This material is based upon work supported by NASA under contract NNM10AA11C issued through the New Frontiers Program. We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible. M.D., C.A. and P.M. acknowledge the French space agency CNES. C.A. and M.D. acknowledge support from ANR “ORIGINS” (ANR-18-CE31-0014). C.A. was supported by the French National Research Agency under the project “Investissements d{\textquoteright}Avenir” UCAJEDI ANR-15-IDEX-01. P.M. acknowledges funding support from the European Union{\textquoteright}s Horizon 2020 research and innovation program under grant agreement number 870377 (project NEO-MAPP) and from Academies of Excellence: Complex Systems and Space, Environment, Risk, and Resilience, part of the IDEX JEDI of Universit{\'e} C{\^o}te d{\textquoteright}Azur. M.P. was supported by the Italian Space Agency (ASI) under ASI-INAF agreement number 2017-37-H.0. S.R.S. is supported by contract number 80NSSC18K0226 as part of the OSIRIS-REx Participating Scientist Program. Publisher Copyright: {\textcopyright} 2020, The Author(s), under exclusive licence to Springer Nature Limited.",
year = "2020",
month = nov,
day = "12",
doi = "10.1038/s41586-020-2846-z",
language = "English (US)",
volume = "587",
pages = "205--209",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Publishing Group",
number = "7833",
}