From SOTT:

Mars’s gullies may be formed by dry ice processes rather than flowing liquid water, as previously thought. This is the conclusion of a study conducted by two French scientists published online on December 21st in Nature Geoscience.

They show that, during late winter and spring, underneath the seasonal CO2 ice layer heated by the sun, intense gas fluxes can destabilize the regolith material and induce gas-lubricated debris flows which look like water-sculpted gullies on Earth.

Since 2000, the cameras in orbit around Mars have transmitted numerous images of small valleys cut into slopes, similar in shape to gullies formed by flowing water on Earth. The gullies seem less than a few million years old-and sometimes less than a few years old. This suggested that significant volumes of liquid water may form on Mars today.

This scenario has recently been questioned by frequent monitoring of the Martian surface by the HiRISE camera aboard NASA Mars Reconnaissance Orbiter. This revealed that gully formation is ongoing on present-day Mars, at seasons when the surface environment of Mars is much too cold for liquid water to flow. However, the observed gully activity seems to occur when CO2 ice (condensed from the atmosphere during winter) is defrosting on the Martian surface. Can the two phenomena be related? If so, how could a thin seasonal dry ice layer deposited above the regolith trigger the formation of decametre-scale debris flows behaving as if they were lubricated by liquid?

To better understand the interaction between the CO2 frost and the surface…

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