Exogenic basalt on asteroid (101955) Bennu

D. Dellagiustina , Hana H. Kaplan , Amy A. Simon , William F. Bottke , Chrysa Avdellidou (1) , Marco Delbo (1) , Ronald-L Ballouz , D. Golish , Walsh K. , H. Campins , Marcel Popescu , Antonella Barucci , Giovanni Poggiali , Daly T. R. , Le Corre Lucile , Vicky Hamilton , Porter N. , E. Jawin , Tim Mccoy , H C Connolly , J.L. Rizos-Garcia , E. Tatsumi , Julia Deleon , Javier Licandro , Sonia Fornasier , M.G. Daly , M.M. Al Asad , L. Philpott , J. Seabrook , Olivier S. Barnouin , Beth Clark , M.C. Nolan , Ellen Howell , R. P. Binzel , Bashar Rizk , D.C. Reuter , Dante Lauretta

1 LAGRANGE - Joseph Louis LAGRANGE

When rubble-pile asteroid 2008 TC3 impacted Earth on October 7, 2008, the recovered rock fragments indicated that such asteroids can contain exogenic material [1,2]. However, spacecraft missions to date have only observed exogenous contamination on large, monolithic asteroids that are impervious to collisional disruption [3, 4]. Here we report the presence of meter-scale exogenic boulders on the surface of near-Earth asteroid (101955) Bennu—the 0.5-km, rubble-pile target of the OSIRIS-REx mission [5] which has been spectroscopically linked to the CM carbonaceous chondrite meteorites [6]. Hyperspectral data indicate that the exogenic boulders have the same distinctive pyroxene composition as the howardite–eucrite–diogenite (HED) meteorites that come from (4) Vesta, a 525-km- diameter asteroid that has undergone differentiation and extensive igneous processing [7, 8, 9]. Delivery scenarios include the infall of Vesta fragments directly onto Bennu or indirectly onto Bennu’s parent body, where the latter’s disruption created Bennu from a mixture of endogenous and exogenic debris. Our findings demonstrate that rubble-pile asteroids can preserve evidence of inter-asteroid mixing that took place at macroscopic scales well after planetesimal formation ended. Accordingly, the presence of HED-like material on the surface of Bennu provides previously unrecognized constraints on the collisional and dynamical evolution of the inner main belt.

Domaines: Planète et Univers [physics]

D. Dellagiustina, Hana H. Kaplan, Amy A. Simon, William F. Bottke, Chrysa Avdellidou, et al.. Exogenic basalt on asteroid (101955) Bennu. Nature Astronomy, 2020, ⟨10.1038/s41550-020-1195-z⟩. ⟨hal-03038593⟩