Formation of recurring slope lineae on Mars by rarefied gas-triggered granular flows

TL;DR

This study proposes that recurring slope lineae on Mars are formed by dry granular flows triggered by rarefied gas movements caused by temperature differences, eliminating the need for liquid water or frost activity.

Contribution

The paper introduces a novel dry process model involving thermal creep of gas in Martian soil to explain slope lineae formation, supported by numerical simulations.

Findings

Gas flow due to thermal creep can disturb soil particles on Mars.

Flow occurs at slopes with specific angles influenced by shadow and heating.

The model aligns with observed locations of slope lineae on Mars.

Abstract

Active dark flows known as recurring slope lineae have been observed on the warmest slopes of equatorial Mars. The morphology, composition and seasonality of the lineae suggest a role of liquid water in their formation. However, internal and atmospheric sources of water appear to be insufficient to sustain the observed slope activity. Experimental evidence suggests that under the low atmospheric pressure at the surface of Mars, gas can flow upwards through porous Martian soil due to thermal creep under surface regions heated by the Sun, and disturb small particles. Here we present numerical simulations to demonstrate that such a dry process involving the pumping of rarefied gas in the Martian soil due to temperature contrasts can explain the formation of the recurring slope lineae. In our simulations, solar irradiation followed by shadow significantly reduces the angle of repose due to the resulting temporary temperature gradients over shaded terrain, and leads to flow at intermediate slope angles. The simulated flow locations are consistent with observed recurring slope lineae that initiate in rough and bouldered terrains with local shadows over the soil. We suggest that this dry avalanche process can explain the formation of the recurring slope lineae on Mars without requiring liquid water or CO2 frost activity.