Transport of Water Into the Polar Regions of Mars Through Scavenging by CO<sub>2</sub> Snowfall
Noora Alsaeed, P. O. Hayne
Abstract
Abstract 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 CO 2 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 CO 2 ice particles and are deposited onto the polar caps during the CO 2 snowfall process. A significant amount of water may thus be contributed to the polar caps in winter through CO 2 snowfall. In this study we use atmospheric retrievals of temperature, pressure, and CO 2 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 CO 2 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.