Transport of Water Into the Polar Regions of Mars Through Scavenging by CO2 Snowfall

The Martian water cycle is tightly coupled to the polar regions, where water in the residual polar caps exchanges with the atmosphere on seasonal and multi-annual timescales. It is thus crucial to understand the mechanisms that control water exchange in the polar regions in order to understand the water cycle as a whole. One such mechanism is CO2 snowfall, which previous studies have shown is frequent in the poles and provides a pathway for material to move from the atmosphere to the surface. We hypothesize that water ice particles that form in the wintertime atmosphere above the polar region act as condensation nuclei (CN) for the CO2 ice particles and are deposited onto the polar caps during the CO2 snowfall process. A significant amount of water may thus be contributed to the polar caps in winter through CO2 snowfall. In this study we use atmospheric retrievals of temperature, pressure, and CO2 ice cloud opacity from the Mars Climate Sounder on board NASA's Mars Reconnaissance Orbiter coupled with a simple cloud settling model to determine sedimentation rates of CO2 ice in the polar winter. We then use these snowfall rates to quantify the amount of water ice deposited to the seasonal polar caps as CN and analyze spatial and temporal patterns in its distribution. We find a lower limit on the average mass of water scavenged every winter on the order of 10(9)-10(10) kg in the north and 10(8)-10(9) kg in the south.

Automated summary

The Martian water cycle is closely linked to the polar regions, particularly through the mechanism of CO2 snowfall. This study uses data and models to estimate that significant amounts of water are deposited onto the polar caps every winter, with around 10^9 - 10^10 kg in the north and 10^8 - 10^9 kg in the south.