For decades, scientists have been speculating about features on Mars that look as if they were carved on the planet’s surface by flowing water. But some gullies in Mars’ polar regions – where temperatures are too low to support liquid water – might not have been carved by liquid, according to an article released yesterday (December 1, 2011) in Geophysical Research Letters.

Instead, sediment lying on top of a seasonal accumulation of carbon dioxide frost could flow like a fluid if the frost sublimes (turns to gas directly from the solid stage) sufficiently quickly. This fluidized sediment could form gullies, according to Yolanda Cedillo-Flores at the Universidad Nacional Autonoma de Mexico in Mexico City and her colleagues.

To determine whether conditions are suitable for such fluidization to occur in Mars’ polar regions, Cedillo-Flores and her team calculated the rate needed for carbon dioxide in the process of sublimation – that is, the process of changing from solid to gas – to fluidize sand and dust lying on top of the carbon dioxide frost.

They then used a computer model of Mars’ surface and subsurface to determine whether buried carbon dioxide frost could potentially sublimate at that rate.

They found that it could. The researchers confirm that sediment fluidization could indeed occur in Mars’ polar regions, and thus, Martian gullies can form without the presence of liquid water.

Bottom line: Gullies carved into the surface of Mars at the Martian poles might have been formed not by flowing water, but by a seasonal accumulation of carbon dioxide frost that sublimed – turned directly from a solid to a gas – according to Yolanda Cedillo-Flores at the Universidad Nacional Autonoma de Mexico in Mexico City and her colleagues.

Read the paper: CO2 gas fluidization in the initiation and formation of Martian polar gullies