Accretion efficiency during planetary collisions

We present the results of smoothed particle hydrodynamic simulations of collisions between two 0.10 M_⊕ differentiated planetary embryos with impact dynamics that are thought to be common to the late stage of terrestrial planet formation. At low impact velocities (υ_imp/ υ_esc < 1.5) and for direct collisions, the impacts are largely accretionary. Inelastic bouncing between embryos with varying degrees of erosion, followed by escape to infinity, is also a common outcome. For dynamical environments typical of most late-stage accretion models, we estimate that more than half of all collisions between like-sized planetary embryos do not result in accumulation into a larger embryo.