A Reappraisal of Subtropical Subsurface Water Ice Stability on Mars

TL;DR

This study revisits the stability of subsurface water ice on Mars at latitudes below 30°, using a new slope microclimate model, and finds that water ice is likely rarer than previously believed in this region.

Contribution

The paper introduces a new slope microclimate model that revises previous estimates of subsurface water ice stability on Mars, especially below 30° latitude.

Findings

Water ice is unlikely to be stable below 30°S due to warmer slopes.

Subsurface water ice may exist at latitudes above 30°S.

Ice deposits could be present down to 25°S on steep dusty slopes.

Abstract

Two arguments have suggested the presence of subsurface water ice at latitudes lower than 30\textdegree~on Mars. First, the absence of CO2 frost on pole-facing slopes was explained by the presence of subsurface ice. Second, models suggested that subsurface ice could be stable underneath these slopes. We revisit these arguments with a new slope microclimate model. Our model shows that below 30{\deg} latitude, slopes are warmer than previously estimated as the air above is heated by warm surrounding plains. This additional heat prevents the formation of CO2 and subsurface water ice for most slopes. Higher than 30{\deg}S, our model suggests the presence of subsurface water ice. In sparse cases (steep dusty slopes), subsurface ice may exist down to 25{\deg}S. While hypothetical unstable ice deposits cannot be excluded by our model, our results suggest that water ice is rarer than previously thought in the +- 30{\deg} latitude range considered for human exploration.