The early impact histories of meteorite parent bodies

Abstract

We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces - compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 - 5% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.