Origin and evolution of the Vesta asteroid family

We model the formation and subsequent collisional evolution of the Vesta asteroid family. The outcomes of the cratering event(s) which generated the family are predicted from current cratering physics, whereas the subsequent erosion of the family members due to collisions with background asteroids is simulated according to the model of Marzari et al. (1995Icar..113..168M). Comparing the size and orbital distribution of the model Vesta families with the observed family, we estimate the number and size of the projectile(s) which have impacted Vesta. The observed morphology of the family suggests two possible scenarios: (1) The family is the outcome of a major cratering event, resulting from the impact of an asteroid =~40km in diameter on the surface of Vesta about 1Gyr ago, and followed by another more recent lower-energy impact (by a projectile =~20km in diameter), producing the family's subgrouping close to the 3:1 mean motion Jovian resonance. (2) A single impact occurred =~1 Gyr ago and formed the whole family at the same time. In this case we have to assume that the fragments were ejected isotropically over a hemispheric region of Vesta, instead of being concentrated near the surface of a 90deg aperture cone, as suggested by laboratory impact experiments with planar targets. This different ejection geometry yields a more scattered distribution of the orbital elements, resulting into a better agreement with the observed family. In both scenarios the cratering event(s) which formed the family is/are likely to have injected a significant number of km-sized and smaller fragments into the 3:1 resonance, thus generating V-type near-Earth asteroids and HED meteorites. However, it appears likely that the current influx of HED meteorites cannot be directly traced back to the family-forming event(s), but results from more recent, smaller impacts on Vesta (or other family members)