Evidence for thermal fatigue on Mars from rockfall patterns on impact crater slopes

Tesson, P.-A.; Conway, S. J.; Mangold, N.; Ciazela, J.; Lewis, S. R. and Mège, D. (2019). Evidence for thermal fatigue on Mars from rockfall patterns on impact crater slopes. In: 50th Lunar and Planetary Science Conference, 18-22 Mar 2019, The Woodlands, Houston, Texas, USA.

URL: https://www.hou.usra.edu/meetings/lpsc2019/pdf/235...

Abstract

Individual block falls are one of the currently active surface processes on Mars. Similarly to Earth, clasts detach from upslope outcrops roll or bounce downslope, leaving a track on the substratum (Fig. 1). The trails show that the rockfalls are recent, as aeolian processes would infill topographic lows over time. Using rover-track erasure rates, these tracks are likely <100 ka.

On Earth, slope instability is usually caused by phase changes of H₂O [1]. However, solar-induced thermal stress could also play a key-role in rock breakdown leading to rockfalls [2]. Although liquid water is not stable at the surface of Mars today, sub-surface water ice is known to be present from mid- to high-latitudes [3]. Water ice and CO₂ seasonal frost on shadowed pole-facing slopes may exist at latitudes down to 30° [4] or less [5]. On the other hand, insolation-related thermal stress has been used to explain fracture orientation patterns in martian boulders observed by the Mars Exploration Rovers [6] and other studies suggest that it could cause rock breakdown on airless bodies [7]. Therefore, both phase transitions and solar-induced thermal stress are plausible mechanisms for rock breakdown and preconditioning slopes for rockfalls on modern Mars. In this study we analyze distribution of rockfalls on impact crater walls to assess whether one of these mechanisms could be involved in local rock breakdown.

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