Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

Sedimentary deposits characterized by the Mars Science Laboratory Curiosity rover provide evidence that Gale crater, Mars intermittently hosted a fluvio-lacustrine environment during the Hesperian. However, estimates of the CO2 content of the atmosphere at the time the sediments in Gale crater were deposited are far less than needed by any climate model to maintain temperatures warm enough for sustained open water lake conditions due to the low solar energy input available at that time. To reconcile some of the in-situ sedimentological evidence for liquid water with climate modeling studies, we perform the water budget of evaporation against precipitation to estimate the minimum lifetimes and the rainfall requirements for open water and ice-covered lakes in Gale crater, for a wide range of pressures and temperatures. We found that both open water and ice-covered lakes are possible, and that ice-covered lakes provide better consistency in regards of the low erosion rates estimates for the Hesperian. We incrementally test the existence of open water conditions using energy balance calculations for the global, regional, and seasonal temperatures, and we assess if the preservation of liquid water was possible under perennial ice covers. We found scenarios where lacustrine conditions are preserved in a cold climate, where the resupply of water by the inflow of rivers and high precipitation rates are substituted by an abutting glacier. For equatorial temperatures as low as 240 K-255 K, the ice thickness ranges from 3 to 10 m, a value comparable to the range of those for the perennially ice-covered lakes in Antarctica (3-6 m). The ice-covered lake hypothesis is a compelling way to decouple the mineralogy and the climate by limiting the gas exchanges between the sediment and the CO2 atmosphere, and it eliminates the requirement for global mean temperatures above the freezing point. Not only do ice-covered lakes provide a baseline for exploring the range of possible lake scenarios for Gale crater during the Hesperian that is fully consistent with climate studies, but also they might have been ideal environments to sustain life on Mars.