Study of Potential Sub-Micrometer-Thick Frost Events and Soil Water Content at Gale Crater

Abstract:

We analyze the highest confidence measurements of relative humidity [1] and ground temperature [2] to identify potential frost events at the surface of Gale Crater during the first 600 sols of the MSL mission. We find that between 4 and 6 am on sols 533, 535, 555, 557, 559 and 560 the ground temperature falls below the calculated frost point. Order-of-magnitude estimate for the thickness of the frost layer indicates that it is of the order of micrometers or less. Additionally, we analyze the relation between water vapor pressure and ground temperature to provide additional constraints on potential frost events and to quantify the exchange of adsorbed water between the surface and the atmosphere.

Adsorbed water could be forced into liquid-like state at the of Gale because van der Waals forces between water ice molecules and mineral surfaces reduces the freezing point [3]. This form of liquid water is relevant to habitability because microorganisms could survive in liquid-like adsorbed water [4].

References:

[1] Harri, Ari-Matti et al., Mars Science Laboratory Relative Humidity Observations – Initial Results (2014), JGR (in press).

[2] Martínez, G. M. et al., Surface Energy Budget and Thermal Inertia at Gale Crater: Calculations from Ground-Based Measurements (2014), JGR (in press).

[3] Möhlmann, D., The influence of van der Waals forces on the state of water in the shallow subsurface of Mars (2008), Icarus 195 (1), 131–139.

[4] Rivkina, E. M. et al., Metabolic activity of permafrost bacteria below the freezing point (2000), Appl. Environ. Microbiol., 66(8), 3230-3233.