Mars Winter: When CO2 Locks the Air into Ice at the Poles

Winter on Mars freezes CO2 from the thin air into a growing polar cap and even dry-ice snow; the cap can store up to about 16% of the atmosphere, causing a global pressure swing of roughly 25%. Temperatures can plunge to around -130°C, with wide local variation by latitude, altitude and surface heat properties. In spring, CO2 sublimates back to gas and pressure rises again as the cap recedes. The northern and southern winters differ due to orbital timing and topography, but the cycle is one integrated CO2 exchange between air and ground.