Effects of Snowfall on the Albedo and Emissivity of Mars' Seasonal Ice Caps

The existence of the residual Carbon Dioxide (CO₂) cap near the south pole of Mars is enabled at least in part by its higher albedo than seasonal CO₂ deposits in northern polar region. Previous studies have suggested that a feasible reason for this contrast in albedos is the different amounts of snowfall at the poles. Snowfall may increase summertime albedo, at the same time it lowers the infrared emissivity of the surface, due to scattering by optically thick clouds and granular surface deposits. Direct observations of the emissivities of the poles can help to understand the possible effects of seasonal snowfall on the polar cap albedo. Snowfall may therefore be an important consideration for modelling the CO₂ cycle on Mars, as well as the planet's long-term climate variations. We used Mars Climate Sounder (MCS) data from the Mars Reconnaissance Orbiter (MRO) to constrain the albedo and emissivity (and in turn snowfall amount) of the seasonal CO₂ deposits in both hemispheres at latitudes > 60° to investigate whether snowfall may be responsible for the higher albedo in the south polar cap. We produced binned polar maps at a resolution of 10 km per pixel for Mars Years 29-33, for emissivity and albedo, and identified all locations with condensed CO₂ on the surface. Using these maps, we quantified the relation between summertime albedo and average wintertime emissivity (as a proxy for snowfall) for each hemisphere. Comparisons between the northern and southern hemispheres revealed important differences. Based on our results, we found that snowfall amount is well-correlated with springtime albedo in within the south polar region, but not in the north polar region. In particular, the highest albedo location on the planet is the south polar residual cap, which also has the greatest snowfall amount in the south polar region. However, there is no such correlation between snowfall and albedo in the northern hemisphere. Indeed, the northern seasonal cap shows significantly greater snowfall amounts than the south, yet lower albedo. Therefore, snowfall is not likely to be the primary factor controlling the hemispheric dichotomy of seasonal cap albedo on Mars.