Rearrangement of Granular Surfaces on Asteroids due to Thermal Cycling

TL;DR

Thermal cycling on asteroid surfaces induces microscopic grain displacements that, over millions of years, can lead to significant material redistribution and surface evolution, affecting the distribution of fine materials and surface features.

Contribution

This study models the effects of thermal cycling on asteroid granular surfaces, revealing potential long-term material flows and surface rearrangements.

Findings

Grains experience micron-scale displacements per cycle.

Thermal cycling can cause centimeter-scale material flow over million-year timescales.

Fine materials may accumulate in depressions due to thermal-driven flows.

Abstract

In granular systems, thermal cycling causes compaction, creep, penetration of dense objects, and ratcheting of grains against each other. On asteroid surfaces, thermal cycling is high amplitude and can happen billions of times in a few million years. We use a 1-dimensional thermophysical conductivity model to estimate the relative displacement of grains in proximity to one another, caused by variations in thermal conductivity or shadows. We find that grains would experience relative displacements of order a few microns during each thermal cycle. If thermal cycling causes diffusive transport, then the asteroid's few centimeters deep thermal skin depth could flow a few centimeters in a million years. Thermal cycling could cause long-distance flows on sloped surfaces, allowing fine materials to collect in depressions.