Simulations of Terrestrial Planet Formation with Strong Dynamical Friction: Implications for the Origin of the Earth’s Water

Overview: We have performed 8 numerical simulations of the final stages of accretion of the terrestrial planets, each starting with over 5×more gravitationally interacting bodies than in any previous simulations. Given the large number of small planetesimals in our simulations, we are able to more accurately treat the effects of dynamical friction during the accretion process. Dynamical friction is the equipartition of energy between large and small bodies in a population, resulting in the damping of relative velocities amongst the large bodies. We studied the effects of the orbits of Jupiter and Saturn on the final planetary systems by running 4 of our simulations with the present, eccentric orbits of Jupiter and Saturn (the EJS simulations) and the other 4 using a nearly circular and co-planar Jupiter and Saturn as predicted in recent models of the evolution of the outer Solar System [1,2,3] (the CJS simulations). We find that the final planets formed in our CJS simulations are much more geochemically consistent with the Earth, primarily in terms of the presence of significant amounts of water as well as in the abundance of siderophile elements in their mantles.