Sublimation kinetics of CO 2 ice on Mars

Dynamic models of the martian polar caps are in abundance, but most rely on the assumption that the rate of sublimation of CO ₂ ice can be calculated from heat transfer and lack experimental verification. We experimentally measured the sublimation rate of pure CO ₂ ice under simulated martian conditions as a test of this assumption, developed a model based on our experimental results, and compared our model's predictions with observations from several martian missions (MRO, MGS, Viking). We show that sun irradiance is the primary control for the sublimation of CO ₂ ice on the martian poles with the amount of radiation penetrating the surface being controlled by variations in the optical depth, ensuring the formation and sublimation of the seasonal cap. Our model confirmed by comparison of MGS-MOC and MRO-HiRISE images, separated by 2-3 martian years, shows that ∼0.4 m are currently being lost from the south perennial cap per martian year. At this rate, the ∼2.4-m-thick south CO ₂ perennial cap will disappear in about 6-7 martian years, unless a short-scale climatic cycle alters this rate of retreat.