Simulator for Formation of Rubble-Pile Asteroids Using Open-Source Physics Simulation.

There are various shapes of rubble-pile asteroids. Ryugu and Bennu have a nearly rotationally symmetric top shape, while Itokawa has an elongated shape. Ground-based telescope observations also suggest that there is much diversity in the shape of the rubble-pile asteroids. It is guessed that the size-frequency distribution of fragments of the parent body and their accumulation conditions contribute the final shape of the rubble-pile asteroids, but the details are not clear.

The purpose of this research is to investigate the relationship between the conditions for rubble-pile accumulation, including the size-frequency distribution of fragments, and the final shape of the asteroid. This investigation is carried out by simulating the accumulation process of rubble-pile asteroids. In the simulation, the fragments are treated as a rigid body, and basic physical interactions such as contact, friction, rotation, and gravity between fragments need to be reproduced. In this research, we decided to implement the reproduction of various physical processe­­s using open-source physics engine Chron (https://projectchrono.org/). Chrono can handle physical interactions between objects of various shapes. In addition, while most physics engines used in games and other applications perform single-precision operations, Chrono is capable of double-precision operations. Ferrari et al. (2017, 2020) were early examples attempting to simulate rubble-pile asteroid formation using Chrono, but they were not discussed well the final shapes of rubble-pile asteroids.

This research aims to implement a simulator using Chrono, following previous research, and to simulate with different parameters such as size-frequency distribution, shape, total number, dynamic friction, static friction, rebound, and rolling resistance coefficient of the fragments. This presentation will report simulator implementation and test simulation results.