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 Letters, doi:10.1029/2011GL049403, 2011 http://dx.doi.org/10.1029/2011GL049403
Title: CO2 gas fluidization in the initiation and formation of Martian polar gullies
Authors: Yolanda Cedillo-Flores: Facultad de Filosofia y Letras, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico and Lunar and Planetary Institute, Houston, Texas, USA;
Allan H. Treiman: Lunar and Planetary Institute, Houston, Texas, USA;
Jeremie Lasue: Lunar and Planetary Institute, Houston, Texas, USA and Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA;
Stephen M. Clifford: Lunar and Planetary Institute, Houston, Texas, USA.
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