Observational evidence for an active surface reservoir of solid carbon dioxide on mars

High-resolution images of the south polar residual cap of Mars acquired in 1999 and 2001 show changes in the configuration of pits, intervening ridges , and isolated mounds. Escarpments have retreated 1 to 3 meters in 1 martia n year, changes that are an order of magnitude larger than can be explained by the sublimation of water ice, but close to what is expected for sublima tion of carbon dioxide ice. These observations support a 35-year-old conjec ture that Mars has a large surface reservoir of solid carbon dioxide. The e rosion implies that this reservoir is not in equilibrium with the present e nvironment and that global climate change is occurring on Mars.