Grain-scale thermoelastic stresses and spatiotemporal temperature gradients on airless bodies, implications for rock breakdown

TL;DR

This study models grain-scale thermoelastic stresses caused by diurnal temperature changes on airless planetary bodies, revealing significant stresses that influence rock breakdown, with implications for planetary geology.

Contribution

The paper introduces a detailed modeling approach of microstructural stresses on airless bodies, highlighting the role of mineral properties and microstructure in rock breakdown processes.

Findings

Peak tensile stresses reach ~100 MPa on the Moon.

Stress amplification occurs at mineral boundaries and pore tips.

Surface temperature gradients are poor proxies for microcrack propagation.

Abstract

Thermomechanical processes such as fatigue and shock have been suggested to cause and contribute to rock breakdown on Earth, and on other planetary bodies, particularly airless bodies in the inner solar system. In this study, we modeled grain-scale stresses induced by diurnal temperature variations on simple microstructures made of pyroxene and plagioclase on various solar system bodies. We found that a heterogeneous microstructure on the Moon experiences peak tensile stresses on the order of 100 MPa. The stresses induced are controlled by the coefficient of thermal expansion and Young's modulus of the mineral constituents, and the average stress within the microstructure is determined by relative volume of each mineral. Amplification of stresses occurs at surface-parallel boundaries between adjacent mineral grains and at the tips of pore spaces. We also found that microscopic spatial and temporal surface temperature gradients do not correlate with high stresses, making them inappropriate proxies for investigating microcrack propagation. Although these results provide very strong evidence for the significance of thermomechanical processes on airless bodies, more work is needed to quantify crack propagation and rock breakdown rates.