Experimentally Induced Thermal Fatigue on Lunar and Eucrite Meteorites – Influence of the Mineralogy on Rock Breakdown

Understanding regolith formation and evolution on airless planetary surfaces at the spatial scale from meters to microns is crucial. Diurnal temperature variations on airless planetary surfaces is a common feature of planetary bodies that play a role in regolith evolution [e.g., Molaro and Byrne, 2012; Delbo et al., 2014]. In a new laboratory experiment we investigated the effects of thermal fatigue in vacuum between 200K and 375K on the lunar anorthosite breccia Northwest Africa (NWA) 11273 and the eucrite Northwest Africa (NWA) 11050. A liquid nitrogen-cooled cryostat is evacuated and predefined temperature cycles are carried out automatically while monitoring the temperature. The samples are investigated via scanning electron microscopy (SEM) and micro-computed tomography after 0, 10, 20, 50, 100, and 400 cycles.

NWA 11050 responds to thermal cycling with the formation and extension of cracks, but the crack formation rate is only ~50% of that for samples studied previously. Lunar anorthosite breccia NWA 11273 shows extensive micro-flaking – a phenomenon reported here for the first time due to thermal stresses. We propose that surfaces exposing solid primary rocks (e.g., eucritic basalts) are less likely producing fine-grained soil by thermal fatigue but larger fragmented (blocky) regolith. Mature regolith rocks with high abundance of (impact) glasses such as the lunar anorthosite breccias are contributing to a fine-grained, tenth-of-µm-sized, soil.

References:

Molaro J. L. and Byrne S., (2012) Journal of Geophysical Research 117:E10.

Delbo M. et al. (2014) Nature 508:233-236.

Warren, P. H., and Korotev, R. L. (2022) Meteoritics & Planetary Science 57:527-557.