Mars atmospheric surface interactions and the CO2 cycle

Mars' northern and southern seasonal polar caps are formed during their respective autumn and winter seasons both by condensation of atmospheric carbon dioxide (CO₂) directly onto the surface, and through atmospheric precipitation in the form of CO₂ snow. During the polar spring and summer, the seasonal ice sublimes, returning CO₂ to the atmosphere.

Roughly 25% of the atmosphere, which is 95% CO₂ by volume, is cycled through the seasonal caps annually. This CO₂ cycle dominates atmospheric circulation on Mars and must be thoroughly understood before the fundamental questions about Mars' climate history and the global distribution of near‐surface water can be addressed.