  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. 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 240K-255K, the
ice thickness ranges from 3-10 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.
