Experimentally induced thermal fatigue on lunar and eucrite meteorites – influence of the mineralogy on rock breakdownOPEN ACCESS
Markus Patzek, Ottaviano Rüsch
JGR Planets
5 October 2022
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“Key Points
- We report on an updated experimental setup to simulate thermal fatigue in high vacuum instead of nitrogen atmosphere to reflect natural conditions
- The crack formation and growth rates differ between the lunar anorthosite and eucritic basalt and are generally <50% of those reported previously
- We propose that the resulting regolith depends highly on the mineralogy of starting materials, which control the breakdown of the rock”
“Thermal fatigue has been proven to be of fundamental importance for the nature and evolution of surfaces of airless bodies in the solar system. It is a rock erosive process acting in conjunction with meteoroid bombardment. We set up an experiment to simulate the diurnal temperature variation at 1 AU of centimeter sized sample cubes using a liquid nitrogen cooled cryostat, allowing to study unexplored conditions, i.e., high vacuum and temperatures of 200 K similar to those occurring on the Moon. The sample cubes are investigated using scanning electron microscopy and micro computed tomography scans before and after 10, 20, 50, 100, and 400 total cycles. Cycling of the lunar anorthosite Northwest Africa (NWA) 11273 and the eucrite NWA 11050 reveal different behaviors: Whereas NWA 11273 responds to the cycling with micro-flaking of tenth-of-µm-sized grains on its surface and only limited crack growth, the eucrite NWA 11050 is less affected by micro-flaking but the growth of cracks is observed to occur throughout the whole experiment. The rate of crack formation and growth is lower when compared to previously reported results on ordinary and carbonaceous chondritic samples carried out under nitrogen atmosphere and above 250 K. We propose that the size of particles and their rate of production by thermal fatigue highly depends on the mineralogy of the exposed rock and areas with mature rocks are prone to produce fine-grained soil, while primary rocks such as basalts are likely to produce blocky regolith in a first step.”
