Formation of gullies on Mars by debris flows triggered by CO₂ sublimation

C. Pilorget , F. Forget (1)

1 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)

Martian gully landforms resemble terrestrial debris flows formed by the action of liquid water and have thus been interpreted as evidence for potential habitable environments on Mars within the past few millennia. However, ongoing gully formation has been detected under surface conditions much too cold for liquid water, but at times in the martian year when a thin layer of seasonal CO₂ frost is present and defrosting above the regolith. These observations suggest that the CO₂ condensation-sublimation cycle could play a role in gully formation. Here we use a thermo-physical numerical model of the martian regolith underlying a CO₂ ice layer and atmosphere to show that the pores beneath the ice layer can be filled with CO₂ ice and subjected to extreme pressure variations during the defrosting season. The subsequent gas fluxes can destabilize the regolith material and induce gas-lubricated debris flows with geomorphic characteristics similar to martian gullies. Moreover, we find that subsurface CO₂ ice condensation, sublimation and pressurization occurs at conditions found at latitudes and slope orientations where gullies are observed. We conclude that martian gullies can result from geologic dry ice processes that have no terrestrial analogues and do not require liquid water. Such dry ice processes may have helped shape the evolution of landforms elsewhere on the martian surface.

Domaines: Planète et Univers [physics]

C. Pilorget, F. Forget. Formation of gullies on Mars by debris flows triggered by CO₂ sublimation. Nature Geoscience, 2016, 9, pp.65-69. ⟨10.1038/ngeo2619⟩. ⟨insu-03727115⟩