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

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.

The Relative Effects of Surface and Subsurface Morphology on the Deflection Efficiency of Kinetic Impactors: Implications for the DART Mission

“…Overall, there is a need to verify the validity of 3D simulations of geologic rubble-pile targets against experiments. Currently, there is a paucity of 3D code validation studies for hypervelocity impacts into rubble-pile targets (Jutzi et al 2022;Ormö et al 2022). However, we note that a 3D validation study is ongoing for iSALE (Ormö et al 2023).…”

“…Previous missions to asteroids indicated that the surface structure and likely the substructure can vary significantly from one asteroid to another (Sullivan et al 2002;Miyamoto et al 2007; Barnouin et al 2019a;Rozitis et al 2020;Jutzi et al 2022). Generally, asteroids are categorized into three categories: solid objects made of strong, cohesive material; rubble piles containing strong pieces within a weaker matrix held together by self-gravity, small particles, and cohesion; and fractured shards consisting of a relatively strong body with large-scale fractures resulting from previous impact events (Bottke et al 2002).…”

“…The momentum carried by the ejecta is a complicated, timedependent, nonlinear function of multiple parameters, including impact angle, surface geology, topography, and target material properties (Housen & Holsapple 2011;Hoerth et al 2013;Raducan et al 2019;Rivkin et al 2021;Jutzi et al 2022;Statler et al 2022;Stickle et al 2022). Therefore, high-fidelity impact simulations are required to understand the relationship between the ejecta momentum and the kinetic impact scenario.…”

The Strength and Shapes of Contact Binary Objects

“…These cohesion values are consistent with observations. On the low end, Bennu and Ryugu have surfaces on the order of 1 Pa cohesion (Jutzi et al 2022;Walsh et al 2022). Other observations show small rubble piles having global strengths of tens to hundreds Pa cohesion (Hirabayashi et al 2014;Rozitis et al 2014;Jewitt et al 2017).…”

Direct N-body Simulations of Satellite Formation around Small Asteroids: Insights from DART’s Encounter with the Didymos System

“…their surfaces and potentially some strength at depth, so this implicit assumption by Sugiura & Kobayashi (2021) is not unreasonable (Barnouin et al 2019;Arakawa et al 2020;Jutzi et al 2022;Walsh et al 2022). However, recent work by Zhang et al (2022) demonstrates that rubble-pile failure mechanisms are highly sensitive to small changes in cohesion at a fixed friction angle and small changes in friction at constant cohesion, indicating that friction and cohesion cannot be combined into a single parameter and should be treated separately.…”