The surface of Mercury is exposed to extreme diurnal thermal variations caused by the high intensity of solar radiation, the radiative loss due to the planet’s lack of atmosphere, its eccentricity and its 3:2 spin - orbit resonance. This work presents an experimental study on terrestrial rocks used as Mercury analogues subjected to hermean conditions. We simulate the power density of a planetary surface at Mercury’s perihelion distance of 0.31 au using the Space and High-Irradiance Near-Sun Simulator (SHINeS) at Luleå University of Technology. The reflectance spectra were acquired in the visible and near-infrared wavelength range for every sample before and after irradiation. Permanent spectral changes are observed in all samples towards the longer wavelengths in the visible spectrum after only one thermal cycle. Darkening is evident in both the visible and near-infrared spectrum ranges, combined with reddening in the visible-to-near-infrared region in most of our samples. We propose that darker samples like boninite, basalt, and diorite are more likely to experience spectral changes due to their low albedo. 

Thermal fatigue is considered a primary mechanism driving rock disaggregation and regolith production on the surface of airless planetary bodies, acting over millions to billions of diurnal temperature cycles. However, its long-term effectiveness has never been experimentally tested. In particular, the Kaiser effect suggests that no additional damage is expected to accumulate when a material is subjected to repeated loading at the same maximum stress level. Here, we use real-time acoustic emission (AE) monitoring to track fracture activity during 100 repeated thermal cycles of ΔT = 190 °C on three meteorites of different petrological type; CM2 Aguas Zarcas, CV3 Allende, and H3-5 Oum Dreyga. The CM2 meteorite exhibited early onset of fracturing activity as indicated by increased AE activity, whereas the CV3 and H3-5 samples showed low activity, with AE occurring predominantly during the later cycles, but ceasing towards the end. These findings suggest that the surfaces of Ch/Cgh-type asteroids, represented by CM2 material, are likely to be more susceptible to thermally driven regolith production, but this response is progressively limited due to threshold-controlled fracturing, whereas S-type bodies, linked to ordinary chondrites, may experience comparatively limited thermal fatigue under similar conditions. CV3 material, analogous to certain anhydrous C-complex/K-type asteroids, likewise appears relatively resistant to damage accumulation across repeated thermal cycles. We propose that thermal fatigue is a threshold-controlled process rather than an indefinitely acting mechanism.

Regolith blocks on asteroid surfaces evolve through several processes, including thermal fatigue: repeated diurnal temperature variations generate thermal stresses and can contribute to progressive rock breakdown. However, the long-term efficiency of thermally-induced fracturing, and its dependence on the material properties of asteroid rocks, remains uncertain. Here we experimentally investigate thermal fatigue in asteroid analogues. We use the ordinary chondrites L3 Aba Panu and LL5 Chelyabinsk and compare their response with CM2 Aguas Zarcas, CV3 Allende, and H3–5 Oum Dreyga meteorites. The samples were subjected to 100 thermal cycles of temperature amplitude ΔT = 190 K, while acoustic emission (AE) monitoring was used to detect fracturing in real time. Our results show that meteorite materials do not respond uniformly to the same imposed thermal cycles. Carbonaceous chondrites show more intense AE activity, whereas ordinary chondrites generate fewer detectable fracture events and reach early saturation plateaus. L3 Aba Panu and LL5 Chelyabinsk remain largely quiet during cycling, suggesting limited progressive damage under the applied conditions. Critically, the AE characteristics show that thermal fatigue damage does not accumulate continuously, but evolves towards material-dependent saturation regimes consistent with stress memory behaviour. AE signal analysis suggests that microcracking is the dominant fracturing process in carbonaceous chondrites, whereas H3–5 activity appears to favour larger fracture events. If these laboratory trends are applicable to their respective parent asteroid materials, thermal fatigue should contribute differently to regolith production on carbonaceous and ordinary chondrite asteroid surfaces, rather than acting as a uniform process across all small bodies.