CO₂ ice caps on  Mars are mantles of CO₂ ice deposited above 50° latitude in both hemispheres during fall and winter. They form by condensation of CO₂ gas, the main constituent of the atmosphere, and can reach thicknesses of 50 cm to 1 m. Their surface temperature is controlled by solid-gas equilibrium with the atmosphere and ranges between 142 and 150 K. In the northern hemisphere, the CO₂ ice cap completely disappears during spring. In the southern hemisphere, the CO₂ ice does not completely sublime, leaving a perennial  polar caps (Mars) 300 km across and several meters thick near the south pole.