Constraining the Potential Liquid Water Environment at Gale Crater, Mars

Abstract

The Mars Science Laboratory (MSL) Rover Environmental Monitoring Station (REMS) has now made continuous in situ meteorological measurements for several Martian years at Gale crater, Mars. Of importance in the search for liquid formation are REMS’ measurements of ground temperature and inâ air measurements of temperature and relative humidity, which is with respect to ice. Such data can constrain the surface and subsurface stability of brines. Here we use updated calibrations to REMS data and consistent relative humidity comparisons (i.e., with respect to liquid versus with respect to ice) to investigate the potential formation of surface and subsurface liquids throughout MSL’s traverse. We specifically study the potential for the deliquescence of calcium perchlorate. Our data analysis suggests that surface brine formation is not favored within the first 1648 sols as there are only two times (sols 1232 and 1311) when humidityâ temperature conditions were within error consistent with a liquid phase. On the other hand, modeling of the subsurface environment would support brine production in the shallow subsurface. Indeed, we find that the shallow subsurface for terrains with low thermal inertia (Î â ²300 J mâ 2 Kâ 1 sâ 1/2) may be occasionally favorable to brine formation through deliquescence. Terrains with Î â ²175 J mâ 2 Kâ 1 sâ 1/2 and albedos of â ³0.25 are the most apt to subsurface brine formation. Should brines form, they would occur around Ls 100°. Their predicted properties would not meet the Special nor Uncertain Region requirements, as such they would not be potential habitable environments to life as we know it.Plain Language SummaryThe Mars Science Laboratory (MSL) has now made continuous measurements of the local weather at Gale crater, Mars. Such measurements can help guide our search for the formation of liquid water on presentâ day Mars. Specifically, when the right temperature and humidity conditions are met, certain salts can take in water vapor from the atmosphere to produce liquids. Here we use data from MSL along with experimental results on the stability of a Marsâ relevant salt to search for time periods when liquids could potentially form at the surface. Additionally, we use simulations and MSL data to understand the potential to form such liquids in the subsurface. Our results suggest that surface formation of liquids is unlikely throughout MSL’s travels; however, the shallow subsurface may experience conditions that would allow for liquid formation. Not much liquid would form, though, and the properties of these liquids would not permit life as we know it to persist.Key PointsMeasured surface environmental conditions at Gale crater are not favorable to brine formation via deliquescence of calcium perchlorateLiquids may have formed in the shallow subsurface of low thermal inertia units within MSLâ traversed terrainsMSL may best find liquids in the subsurface of units with thermal inertia less than or equal to 175 J mâ 2 Kâ 1 sâ 1/2 and albedo > 0.25 around Ls 100°