A Reappraisal of Subtropical Subsurface Water Ice Stability on Mars

Abstract

Abstract Massive reservoirs of subsurface water ice in equilibrium with atmospheric water vapor are found poleward of 45° latitude on Mars. The absence of CO2 frost on steep pole‐facing slopes and simulations of atmospheric‐soil water exchanges suggested that water ice could be stable underneath these slopes down to 25° latitude. We revisit these arguments with a new slope microclimate model. Our model shows that below 30° latitude, slopes are warmer than previously estimated as the air above is heated by warm surrounding plains. This additional heat prevents the formation of surface CO2 frost and subsurface water ice for most slopes. Our model suggests the presence of subsurface water ice beneath pole‐facing slopes down to 30° latitude, and possibly 25° latitude on sparse steep dusty slopes. While unstable ice deposits might be present, our results suggest that water ice is rarer than previously thought in the ±30° latitude range considered for human exploration.