Gullies on Mars can be formed by dry carbon dioxide and do not need liquid water.
Planetary scientists have been excited about gullies on Mars's surface (pictured) because they look like they could have been formed recently by flowing water — possibly making the planet habitable. Cedric Pilorget at Paris-Sud University and François Forget of the Sorbonne Universities in Paris used a numerical model to simulate a layer of CO2 ice sitting on top of the Martian soil and in pores within it. They calculated that as the Martian winter turns to spring, the ice turns to gas, destabilizing the surface and causing it to crumble and form the gullies.
The work bolsters the idea that many Martian landforms can be created by dry geological processes that do not require water.
Nature Geosci. http://dx.doi.org/10.1038/ngeo2619 (2015)
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No water needed for Mars gullies. Nature 528, 439 (2015). https://doi.org/10.1038/528439e
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DOI: https://doi.org/10.1038/528439e
