Exogenic basalt on asteroid (101955) Bennu
Résumé
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
| Origine | Fichiers produits par l'(les) auteur(s) |
|---|---|
| Licence |