Temporal variability of thermal-cycling induced fracturing in chondrites
N. Latsia1, J. Borg1, E. Kaufmann1, M. Granvik1,2 and A. Hagermann11Luleå University of Technology2
University of HelsinkiRegolith on asteroid surfaces was thought to be a result of micrometeoroid impacts [1], but some recent studies [2,3] claim that
thermal fatigue is the dominant regolith production process on airless bodies. Thermal fatigue is produced by diurnal and/or
annual variations on the surface temperature of asteroids and its efficiency depends on the heliocentric distance, the rotation
period, and the thermal inertia of the asteroid’s surface. A fundamental assumption of previous studies is that thermal fatigue
remains effective over thousands, or even millions, of thermal cycles. However, the Kaiser effect, extensively studied in thefield of fracture mechanics on terrestrial rocks, states that fracturing on materials ceases when previously exerted load levels
are not exceeded [9]. Previous research has demonstrated that the thermal properties of CM2 chondrites depend on theirmineralogy [11]. Thus, the thermal expansion coefficient of each mineral at specific temperature changes can be translated into
different mechanical loads resulting from thermal fatigue.
We aim to observe the time-resolved crack propagation induced by thermal stresses over subsequent thermal load cycles inmeteorites – acting as asteroid analogues – in order to understand the role of thermal fatigue in eroding asteroid surfaces.
According to several studies, Ryugu is similar to CI [5,6,7,8] and CM [8] carbonaceous chondrites, and hence provides groundtruth observations for these samples. We investigate CI, CM, and, for comparison, LL chondrites to examine the behaviour ofthermal fatigue on different petrographic types of meteorites. The samples are subjected to a minimum of 100 cycles at
ΔT=210K as the temperature variation of C-type NEAs is 200K [2]. To identify the spatial occurrence of pre-existing andpropagating cracks, the samples are scanned using X-ray tomography.
We aim to use non-destructive testing (NDT) methods to detect the time and frequency of crack initiation and propagation.
NDT methods are used in many industries to identify and characterize the integrity of a material’s surface and interior without
interfering with its destruction [10]. The Kaiser effect predicts a decrease in the number of produced stresses as the number ofthermal cycles increases, considering that the previous maximum and minimum temperatures of each cycle remain constant at
170Co and -40Co respectively. If the Kaiser effect is applicable, we expect to see the effects of thermal fatigue wane after a few
thermal cycles, suggesting that other mechanisms, such as chemical alteration, are contributing to the breakdown process ofasteroids.
References[1] Housen K.R. et al. 1979. Icarus 39(3) 317-351. [2] Delbo M. et al. 2014. Nature 508(7495) 233-236. [3] Molaro J.L. et al.
2015. JGR Planets 120(2) 255-277. [4] Sakatani N. et al. 2021. Nature Astron 5(8) 766-774. [5] Yokoyama T. et al. 2022.
Science 379(6634) abn7850. [6] Yada et al. 2022. Nature Astron 5(3) 214-220. [7] Kitazato K. et al. 2021. Nature Astron 5(3)246-250. [8] Grott M. et al. 2020. JGR 125(12) e2020JE006519. [9] Kaiser J. 1950. A study of acoustic phenomena in tensile
heat (PhD Thesis). [10] Dwivedi K. S. et al. 2017. Materials Today 5(2) 3690-3698. [11] Opeil C.P. et al. 2020. MAPS 55(8).