Constraining surface properties of asteroid (162173) Ryugu from numerical simulations of Hayabusa2 mission impact experiment

TL;DR

This study uses numerical simulations to analyze the impact experiment on asteroid Ryugu, revealing insights into its surface properties, cohesion effects, and implications for the asteroid's geological age.

Contribution

It introduces a novel numerical simulation approach to understand low-gravity impact cratering and surface cohesion effects on asteroid Ryugu.

Findings

Target cohesion may be very low.

Impact occurred in the transitional cratering regime.

Surface ages of Ryugu's geological units may vary due to cohesion.

Abstract

The Hayabusa2 mission impact experiment on asteroid Ryugu created an unexpectedly large crater. The associated regime of low-gravity, low-strength cratering remained largely unexplored so far, because these impact conditions cannot be re-created in laboratory experiments on Earth. Here we show that the target cohesion may be very low and the impact probably occurred in the transitional cratering regime, between strength and gravity. For such conditions, our numerical simulations are able to reproduce the outcome of the impact on Ryugu, including the effects of boulders originally located near the impact point. Consistent with most recent analysis of Ryugu and Bennu, cratering scaling-laws derived from our results suggest that surfaces of small asteroids must be very young. However, our results also show that the cratering efficiency can be strongly affected by the presence of a very small amount of cohesion. Consequently, the varying ages of different geological surface units on Ryugu may be due to the influence of cohesion.