# The Origins of Asteroidal Rock Disaggregation: Interplay of Thermal Fatigue and Microstructure

## TL;DR

This study investigates how thermal fatigue and microstructure influence rock disaggregation on asteroids, providing insights into regolith formation and distinguishing thermally induced fragments from impact products.

## Contribution

It introduces a microstructure-based finite element model to explain thermal fatigue crack propagation in asteroid-like rocks, supported by experimental observations.

## Key findings

- Cracks preferentially follow mineral interfaces leaving them intact.
- Thermal cycling causes crack growth that depends on microstructure.
- Model accurately predicts crack paths observed experimentally.

## Abstract

The distributions of size and chemical composition in the regolith on airless bodies provides clues to the evolution of the solar system. Recently, the regolith on asteroid (25143) Itokawa, visited by the JAXA Hayabusa spacecraft, was observed to contain millimeter to centimeter sized particles. Itokawa boulders commonly display well-rounded profiles and surface textures that appear inconsistent with mechanical fragmentation during meteorite impact; the rounded profiles have been hypothesized to arise from rolling and movement on the surface as a consequence of seismic shaking. We provide a possible explanation of these observations by exploring the primary crack propagation mechanisms during thermal fatigue of a chondrite. We present the in situ evolution of the full-field strains on the surface as a function of temperature and microstructure, and observe and quantify the crack growth during thermal cycling. We observe that the primary fatigue crack path preferentially follows the interfaces between monominerals, leaving them intact after fragmentation. These observations are explained through a microstructure-based finite element model that is quantitatively compared with our experimental results. These results on the interactions of thermal fatigue cracking with the microstructure may ultimately allow us to distinguish between thermally induced fragments and impact products.