THERMAL WEATHERING AND BEDROCK EROSION ON AIRLESS BODIES (Invited Presentation)

Thermal stress weathering may play a role in the evolution of terrestrial landscapes, particularly those without atmospheres, by contributing to regolith production and crater degradation. Damage occurs in the form of microscopic cracks that result from a thermal cycle or thermal shock. Many studies evaluate this process by measuring the rate of surface temperature change (dT/dt), and assuming damage occurs when this quantity exceeds a threshold of 2 K/min. In reality, due to natural variation in diurnal and annual thermal forcing, and the complexity of the rock structure at small scales, subsurface stress fields induced by surface temperature variations are extremely complex. This makes a constant threshold value rather uninformative in determining damage, but still useful in determining relative efficacy of the process on different planetary surfaces. Here we report on thermal modeling to quantify rates of temperature change throughout the inner solar system to improve our understanding of what surfaces may be most susceptible to this process.

Our thermal modeling results indicate that the magnitude of dT/dt values on airless bodies is primarily controlled by two factors: the length of its sunrise and/or sunset on quickly rotating bodies, such as Vesta, and by distance to the sun on slowly rotating bodies, such as Mercury. The strongest temperature shocks are experienced by highly sloped east- or west-facing surfaces. Hot thermal shocks (dT/dt>0) tend to be stronger than cold shocks (dT/dt<0), and on some bodies, daytime shadowing from surrounding topography may produce higher dT/dt values than those caused by diurnal sunrise/set. However, we also found that high dT/dt values are not always correlated with high temperature gradients within the rock. This adds to the ambiguity of the poorly understood damage threshold.

To gain a better understanding of the relationship between the temporal and spatial temperature gradients, as well as gradients required to cause damage, future work will include modeling the process on a microphysical level using Finite Element Analysis of Microstructures (OOF), software developed by NIST. We will report rates of temperature change on airless bodies in the inner solar system and preliminary results of thermal stresses and potential damage that may be experienced by these surfaces.