TY  - JOUR
A1  - Patzek, Markus
A1  - Rüsch, Ottaviano
T1  - Experimentally Induced Thermal Fatigue on Lunar and Eucrite Meteorites—Influence of the Mineralogy on Rock Breakdown
Y1  - 2022-10-07
VL  - 127
IS  - 10
JF  - Journal of Geophysical Research: Planets
DO  - 10.1029/2022JE007306
PB  - 
N2  - 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, that is, 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.
N2  - Plain Language Summary: Thermal fatigue—the fatigue of a material due to temperature variation—is important for the breakdown of rocks on the surface of planetary bodies such as the Moon, asteroids, and also on the Earth and the formation of a fine‐grained soil, called the regolith. With an improved experimental setup, we simulate the diurnal temperature variations at a solar distance of 1 AU under high vacuum conditions between 200 and 375 K for the lunar anorthosite breccia Northwest Africa (NWA) 11273 and the eucritic basalt NWA 11050. We show that both types of rocks respond different to these temperature excursions: The basaltic eucrite forms cracks over the course of 400 cycles and the lunar anorthosite tends to flake off tenth‐of‐µm‐sized grains with only limited cracking. The overall obtained cracking rates are lower when compared to those from previous experiments under nitrogen atmosphere, indicating the retrieved breakdown rates are lower than previously reported and the type of resulting soil depends strongly on the mineralogy of the exposed rock.
N2  - 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.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/10440
ER  -