A comparison of CO₂ seasonal activity in Mars' northern and southern hemispheres

Carbon dioxide is Mars' most active volatile. The seasonal and diurnal processes of when and where it condenses and sublimates are determined by energy balance between the atmosphere and surface ice in Mars' vapor pressure equilibrium climate. Mars' current obliquity ensures that the polar caps are stable locations for seasonal condensation. The eccentricity of Mars' orbit is the major driver of differences in seasonal behavior of CO₂ between the northern vs southern hemisphere. In particular, the current positions of perihelion and aphelion, in addition to the large elevation difference between the poles, dominate the ways seasonal processes transpire in the two hemispheres. We summarize and discuss the unprecedented observations of these processes that have been collected by the Mars Reconnaissance Orbiter over the last 8.5 Mars Years. The longer southern fall and winter allows more time for CO₂ ice to accumulate and densify in the southern hemisphere. Northern winter coincides with the perihelion dust storm season, thus the north polar seasonal ice deposits are expected to contain a greater concentration of dust in relation to CO₂ and H₂O ices. With less time for densification and more contaminants the northern seasonal layer of CO₂ ice is likely weaker than the southern layer.