Asteroids under stress

Airless planetary bodies experience repeated diurnal temperature variations that generate cyclic thermal stresses in surface rocks. These stresses can drive thermal fatigue, a process considered important for rock breakdown and regolith production on asteroid surfaces [1,2]. However, the long-term effectiveness of thermal fatigue, and whether it remains efficient across different asteroid materials, remains poorly constrained. We experimentally investigate thermal fatigue in the ordinary chondrites L3 Aba Panu and LL5 Chelyabinsk by subjecting them to 100 thermal cycles with a temperature amplitude of ΔT = 190 K. Acoustic emission monitoring was used to detect real-time fracturing. Our results show that both ordinary chondrites produce very limited fracture activity, reaching early saturation plateaus, an indication of a strong stress-memory effect. Extending these observations to the meteorite dataset from previous studies [3], Figure 1 shows that the porous carbonaceous chondrites CM2 Aguas Zarcas and CV3 Allende, generate higher cumulative AE activity, whereas the ordinary chondrite H3-5 shows intermediate activity, and L3 and LL5 meteorites reach plateaus early during thermal cycling.   We therefore quantify the efficiency of thermal fatigue across lithologies and show that asteroid surface breakdown is material dependent.We additionally use Rise Amplitude – Average Frequency (RA-AF) analysis to evaluate the source characteristics of thermally induced cracking. Our findings indicate no systematic difference between heating and cooling related acoustic emission events, suggesting that fracture behaviour is not controlled by the direction of temperature change. However, the RA-AF distributions show differences in fracture behaviour between meteorite types. We conclude that porous carbonaceous chondrites are more susceptible to thermally driven breakdown that the ordinary chondrites investigated here.  Figure  1. Cumulative acoustic emission hits as a function of thermal cycle number for five meteorite samples subjected to repeated thermal cycling. Periods of rapid increase correspond to increased fracture activity. Plateaus indicate intervals with little or no detectable fracturing.[1] Delbo M., Libourel G., Wilkerson J., Murdoch N., Michel P., Ramesh K.T., Ganino C., Verati C., Marchi S., Nature 2014, 508, 233–236.[2] Molaro J.L., Byrne S., Langer S.A., Journal of Geophysical Research: Planets 2015, 120, 255–277.[3] Latsia N., Kaufmann E., Tsirvoulis G., Suhonen H., Granvik M., Borg J., Hagermann A., Icarus 2026, 455, 117130.