Temperature Oscillations About the Freezing Point and Ice Formation on the Evaporation Rate of Water on Mars

We report measurements of the evaporation rate of water under Mars-like conditions (CO2 atmosphere at 7 mbar and 0°C) in which small temperature oscillations about the freezing point repeatedly formed and removed a thin layer of ice. We found that the average evapo-ration at 2.7 0.5°C without an ice layer (corrected for the difference in gravity on Earth and on Mars) was 1.24 0.12 mm/h, while at 2.1 0.3°C with an ice layer the average evapora-tion rate was 0.84 0.08 mm/h. These values are in good agreement with those calculated for the evaporation of liquid water and ice when it is assumed that evaporation only depends on diffusion and buoyancy. Our findings suggest that such differences in evaporation rates are entirely due to the temperature difference and that the ice layer has little effect on evapora-tion rate. We infer that the formation of thin layers of ice on pools of water on Mars does not significantly increase the stability of water on the surface of Mars. Key Words: Water—Ice— Mars—Evaporation rate. Astrobiology 6, xxx–xxx. 64