Particle Number Dependence of the N-body Simulations of Moon Formation

The formation of the Moon from the circumterrestrial disk has been investigated by using N-body simulations with the number N of particles limited from 10(4) to 10(5). We develop an N-body simulation code on multiple Pezy-SC processors and deploy Framework for Developing Particle Simulators to deal with large number of particles. We execute several high- and extra-high-resolution N-body simulations of lunar accretion from a circumterrestrial disk of debris generated by a giant impact on Earth. The number of particles is up to 10(7), in which 1 particle corresponds to a 10 km sized satellitesimal. We find that the spiral structures inside the Roche limit radius differ between low-resolution simulations (N <= 10(5)) and high-resolution simulations (N >= 10(6)). According to this difference, angular momentum fluxes, which determine the accretion timescale of the Moon also depend on the numerical resolution.