Bulk chemical and Hf–W isotopic consequences of incomplete accretion during planet formation

Abstract

Late-stage accretion involves collisions which may result in complete or incomplete merging of the two objects, hit-and-run encounters, or mass loss from the target. We use a recent N-body study incorporating these different collision styles (Chambers, J.E. [2013]. Icarus 224, 43–56) to investigate how collision style affects the bulk chemical and isotopic outcomes of terrestrial planet formation. Compared with simulations in which all collisions result in perfect mergers, the variability in modeled silicate mass fraction and tungsten isotope anomaly is larger, especially for lower-mass planets. The final tungsten anomaly also shows a systematic reduction, because the timescale to finish planet growth is longer when incomplete mergers are included. Simulations including incomplete merging can reproduce the observed scatter in both tungsten anomaly and silicate mass fraction of the terrestrial planets.