Formation of Martian gullies by avalanches of seasonal CO₂ frost

Abstract

Although the existence of liquid water on Mars cannot be expected under its present dry and thin atmospheric conditions, observations of the recent Martian gully-like features associated with fluid flows suggest the existence of liquid water on or near the surface of Mars. However, if Martian gullies were not formed in the recent past but are forming even today, liquid water would not be responsible for the formation of the gullies. CO₂ is the most volatile element prevalent on Mars; and it condenses on the ground surface as seasonal frost with a decrease in the ground surface temperature. Certain MOC images in springtime show views of possible avalanches of CO₂ frost on the walls of the polar pits, and suggest that the CO₂ avalanches, such as powder flows or granular flows, could possibly dissect local slopes and develop gullies. In this study, we calculate the thickness of the CO₂ frost condensed on local slopes as a function of latitude and obliquity by using an energy balance model that takes into consideration the effects of the local slopes. The results show a significant correlation between the latitudinal distribution of the orientations of gullied slopes and that of the slopes covered with seasonal CO₂ frost.