Particle Number Dependence of The $N$-Body Simulations of Moon Formation

TL;DR

This study uses high-resolution N-body simulations to investigate how the number of particles affects the formation process and timescale of the Moon from a circumterrestrial debris disk.

Contribution

Developed a scalable N-body simulation code on multiple processors and explored the impact of particle number on lunar accretion modeling.

Findings

Spiral structures vary with simulation resolution.

Angular momentum fluxes depend on particle number.

Higher resolution simulations show different accretion dynamics.

Abstract

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 FDPS (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-size satellitesimal. We find that the spiral structures inside the Roche limit radius differ between low-resolution simulations ($N \leq10^5$) and high-resolution simulations ($N \geq10^6$). According to this difference, angular momentum fluxes, which determine the accretion timescale of the Moon also depend on the numerical resolution.