Stratigraphy and evolution of the buried CO₂ deposit in the Martian south polar cap

Abstract Observations by the Shallow Radar instrument on Mars Reconnaissance Orbiter reveal several deposits of buried CO 2 ice within the south polar layered deposits. Here we present mapping that demonstrates this unit is 18% larger than previously estimated, containing enough mass to double the atmospheric pressure on Mars if sublimated. We find three distinct subunits of CO 2 ice, each capped by a thin (10–60 m) bounding layer (BL). Multiple lines of evidence suggest that each BL is dominated by water ice. We model the history of CO 2 accumulation at the poles based on obliquity and insolation variability during the last 1 Myr assuming a total mass budget consisting of the current atmosphere and the sequestered ice. Our model predicts that CO 2 ice has accumulated over large areas several times during that period, in agreement with the radar findings of multiple periods of accumulation.