Deposition of CO₂ and erosion of the Martian south perennial cap between 1972 and 2004: Implications for current climate change

We present a comparison of Mariner 9, Viking, Mars Orbiter Camera, and Mars Odyssey Thermal Emission Imaging System visible and infrared images of the south perennial cap taken during the summer between 1972 and 1977 and between 1999 and 2004. Between 1972 and 1977, the lateral expansion and the reduction of the patchiness of the cap indicate that CO₂ ice was deposited. During subsequent years, the distribution of the CO₂ ice has been modified by the erosion and deposition Of CO₂ on the cap at the kilometer scale. Because vertical deposition Of CO₂ on the cap is only detected when the patchiness decreases as observed between 1972 and 1977, present deposition on the cap would not be detectable and cannot be ruled out. Therefore the current lateral erosion of the walls of the CO₂ cap at the meter scale is not a sufficient observation to conclude that the climate is changing on Mars. The present mass balance of the cap cannot be estimated from available south polar cap images, and it is not possible to determine with the existing data if the climate of Mars is changing.