Scaling forces to asteroid surfaces: The role of cohesion

TL;DR

This paper investigates the dominance of van der Waals cohesive forces over gravity and other forces on asteroid surfaces, proposing a new model for asteroid surface composition and behavior based on these forces.

Contribution

It introduces a scaling analysis showing cohesion dominates on asteroid surfaces and proposes a new model for asteroid end states involving fine regolith held by cohesion.

Findings

Cohesive forces surpass gravity and electrostatic forces on asteroid surfaces.

Terrestrial experiments on cohesive powders are relevant for asteroid surface processes.

A new model suggests small, fast-rotating asteroids are held together by cohesion.

Abstract

The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces.