Olivine on Vesta as exogenous contaminants brought by impacts: Constraints from modeling Vesta’s collisional history and from impact simulationsOPEN ACCESS
D. Turrini, V. Svetsov, G. Consolmagno, S. Sirono, S. Pirani
Icarus
In Press, Accepted Manuscript, Available online 25 July 2016
“Highlights
• The Dawn mission revealed the presence of olivine on the surface of asteroid Vesta
• Olivine appears at a handful of small outcrops associated to post-Rheasilvia craters
• We investigate the delivery of olivine by impacts and its compositional signature on Vesta’s surface
• The flux of A-type and S-type asteroids on Vesta can explain Dawn’s observations
• No significant olivine excavation from the mantle is required over the life of Vesta”
“The survival of asteroid Vesta during the violent early history of the Solar System is a pivotal constraint on theories of planetary formation. Particularly important from this perspective is the amount of olivine excavated from the vestan mantle by impacts, as this constrains both the interior structure of Vesta and the number of major impacts the asteroid suffered during its life. The NASA Dawn mission revealed that olivine is present on Vesta’s surface in limited quantities, concentrated in small patches at a handful of sites not associated with the two large impact basins Rheasilvia and Veneneia. The first detections were interpreted as the result of the excavation of endogenous olivine, even if the depth at which the detected olivine originated was a matter of debate. Later works raised instead the possibility that the olivine had an exogenous origin, based on the geologic and spectral features of the deposits. In this work we quantitatively explore the proposed scenario of a exogenous origin for the detected vestan olivine to investigate whether its presence on Vesta can be explained as a natural outcome of the collisional history of the asteroid over the last one or more billion years. To perform this study we took advantage of the impact contamination model previously developed to study the origin and amount of dark and hydrated materials observed by Dawn on Vesta, a model we updated by performing dedicated hydrocode impact simulations. We show that the exogenous delivery of olivine by the same impacts that shaped the vestan surface can offer a viable explanation for the currently identified olivine-rich sites without violating the constraint posed by the lack of global olivine signatures on Vesta. Our results indicate that no mantle excavation is in principle required to explain the observations of the Dawn mission and support the idea that the vestan crust could be thicker than indicated by simple geochemical models based on the Howardite-Eucrite-Diogenite family of meteorites.”
