A Reappraisal of Subtropical Subsurface Water Ice Stability on Mars

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.

Modeling Slope Microclimates in the Mars Planetary Climate Model

“…These two effects increase the slope energy budget by nearly 10 W m −2 , with significant consequences for CO 2 frost extent. A more accurate description and demonstration of these two effects and their consequences are discussed in a companion paper (Lange, Forget, Vincendon, et al., 2023, accepted for publication in GRL). As discussed in Sections 3.4.4 and 3.4.5, this assumption of a “shared” atmosphere, mostly in equilibrium with the flat surfaces, might lead to a small overestimation of the downwelling infrared flux, as cold air can, for instance, be confined within a crater by katabatic slope winds during the night and early morning.…”

“…This may be due to the fact that our model considers the surrounding plains that warm the atmosphere, increasing the downwelling infrared flux and therefore the surface temperature. Such effects, which were not considered in , and their consequences are discussed in Section 6.1 and are more detailed in a companion paper (Lange, Forget, Vincendon, et al, 2023, accepted for publication in GRL).…”

“…With this approach, we simulate for the first time the distribution of the ice table underneath slopes but also flat surfaces with a complete GCM for the atmosphere and the (sub)surface. The results are presented in a dedicated paper (Lange, Forget, Vincendon, et al., 2023).…”

“…Such effects, which were not considered in Vincendon, Mustard, et al. (2010), and their consequences are discussed in Section 6.1 and are more detailed in a companion paper (Lange, Forget, Vincendon, et al., 2023, accepted for publication in GRL).…”