The Strength of Regolith and Rubble Pile Asteroids

TL;DR

This paper proposes that small rubble pile asteroids possess a non-zero cohesive strength due to van der Waals forces, which influences their rotational stability and explains observed properties of small asteroids.

Contribution

It introduces a simple model for asteroid strength based on weak inter-grain forces, validated through simulations and lunar regolith comparisons.

Findings

Cohesive strength is constant regardless of asteroid size.

Rapidly rotating asteroids may be either rubble piles or monolithic boulders.

The model explains properties of small NEA and Main Belt asteroids.

Abstract

We explore the hypothesis that, due to small van der Waals forces between constituent grains, small rubble pile asteroids have a small but non-zero cohesive strength. The nature of this model predicts that the cohesive strength should be constant independent of asteroid size, which creates a scale dependence with relative strength increasing as size decreases. This model counters classical theory that rubble pile asteroids should behave as scale-independent cohesionless collections of rocks. We explore a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith, and then explore its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations, and in particular of asteroid 2008 TC3. One conclusion is that the population of rapidly rotating asteroids could consist of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders.