Temporal evolution of fracturing in chondrites induced by thermal cycling

Thermal fatigue on asteroids is driven by diurnal and/or annual surface temperature variations, with its efficiency depending on the heliocentric distance, the rotation period, and the thermal and optical properties of the asteroid’s surface. Earlier studies [1,2] suggest that thermal fatigue remains effective over thousands, or even millions, of temperature cycles, contributing to the gradual breakdown of surface rocks. Other studies are somewhat more inconclusive [3]. The detailed timing and progression of crack propagation during repeated thermal cycling remain insufficiently understood. In fracture mechanics, the Kaiser effect, well known from studies on terrestrial rocks, suggests that fracturing on materials ceases unless the stress applied exceeds previous levels [3]. In the context of thermal fatigue, differences in the thermal expansion coefficients of individual minerals under changing temperatures can generate varying internal stresses within the rock.

In this study, we investigate the time-resolved development of cracks induced by thermal stresses in meteorites, acting as analogues for asteroid material, to better understand the role of thermal fatigue in regolith production. We have subjected different petrographic types of meteorites to 100 thermal cycles of ΔT=190 K. The meteorites used are CM2 Aguas Zarcas, CV3 Allende, LL5 Chelyabinsk, L5 Sayh al Uhaymir, L3 Aba Panu, and H3-5 Oum Dreyga. Acoustic emission monitoring is used to detect and temporally resolve microcracking events, while X-ray μCT scanning is applied to visualise the spatial distribution of pre-existing and propagating fractures at the start and end of each thermal cycling experiment. A comparison of XCT scans before and after the thermal cycling will reveal the extent and progression of fracture development.

 

[1] Delbo M. et al. 2014. Nature 508(7495) 233-236. [2] Molaro J.L. et al. 2015. JGR Planets 120(2) 255-277. [3] Patzek M et al. 2024. JGR Planets, 129(1). [4] Kaiser J. 1950. A study of acoustic phenomena in tensile heat (PhD Thesis).