Martian gully landforms, indicative of rapid flow of sediment down steep slopes, have been cited as evidence of the action of near-surface liquid water in Mars' recent past. But Gullies in the cold polar regions cannot involve pure liquid water. A new study show that polar gullies could be initiated by fluidization of sediment over a subliming seasonal deposit of CO₂ frost, as has been proposed previously.

Gullies on Mars have been pointed to as evidence for the presence of flowing liquid water. However, gullies also exist in Mars’ polar regions, where temperatures are too low to support liquid water. Other processes have been proposed to explain the origin of gullies but have not been confirmed. For instance, 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.

To determine whether conditions are suitable for such fluidization to occur in Mars’ polar regions, Cedillo-Flores et al. calculated the carbon dioxide sublimation rate needed to fluidize sand and dust lying on top of the carbon dioxide frost. They then used a thermal model of Mars’ surface and subsurface to determine whether buried carbon dioxide frost could potentially sublimate at that rate. 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.

Source: Geophysical Research Lettershttp://dx.doi.org/10.1029/2011GL049403