Water and Brines on Mars: Current Evidence and Implications for MSL

Abstract

Liquid water is a basic ingredient for life as we know it. Therefore, in order to understand the habitability of other planets we must first understand the behavior of water on them. Mars is the most Earth-like planet in the solar system and it has large reservoirs of H 2 O. Here, we review the current evidence for pure liquid water and brines on Mars, and discuss their implications for future and current missions such as the Mars Science Laboratory.Neither liquid water nor liquid brines are currently stable on the surface of Mars, but they could be present temporarily in a few areas of the planet. Pure liquid water is unlikely to be present, even temporarily, on the surface of Mars because evaporation into the extremely dry atmosphere would inhibit the formation of the liquid phase, where the temperature and pressure are high enough so that water would neither freeze nor boil. The exception to this is that monolayers of liquid water, referred to as undercooled liquid interfacial water, could exist on most of the Martian surface. In a few places liquid brines could exist temporarily on the surface because they could form at cryogenic temperatures, near ice or frost deposits where sublimation could be inhibited by the presence of nearly saturated air.Both liquid water and liquid brines might exist in the shallow subsurface because even a thin layer of soil forms an effective barrier against sublimation allowing pure liquid water to form sporadically in a few places, or liquid brines to form over longer periods of time in large portions of the planet. At greater depths, ice deposits could melt where the soil conductivity is low enough to blanket the deeper subsurface effectively. This could cause the formation of aquifers if the deeper soil is sufficiently permeable and an impermeable layer exists below the source of water.The fact that liquid brines and groundwater are likely to exist on Mars has important implications for geochemistry, glaciology, mineralogy, weathering and the habitability of Mars.

Transient liquid water and water activity at Gale crater on Mars

“…5shows its evolution through seasons. It is in agreement with past mission models11 and with the profile expected by GCM simulations for the lowest boundary-layer height of the models (at 5 m; ref. 20; seeFig.…”

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

“…[104]). The presence of liquid water, a key ingredient for life, has been postulated on planets and moons within our Solar System, including Enceladus, Europa and Mars [105][106][107][108][109]. The findings of the WISSARD project further support the idea that life can exist wherever liquid water and suitable substrates are present, and that energy from sunlight is not required to support that life.…”

The Modern Near-Surface Martian Climate: A Review of In-situ Meteorological Data from Viking to Curiosity

“…Mars has large reservoirs of water as ice and vapor, but pure liquid water is unlikely to be present, even temporarily, on the surface of Mars because it would quickly evaporate in the regions where it neither freezes nor boils (Ingersoll 1970;Haberle et al 2001;Martínez and Renno 2013). However, the presence of water ice in the shallow subsurface midlatitude and polar regions Mitrofanov et al 2002;Byrne et al 2009), along with the detection of perchlorates in polar and equatorial soil Glavin et al 2013;Ming et al 2014) and of chloride-bearing deposits in the southern highlands at low and midlatitudes (Osterloo et al 2008), is important because they can melt this ice at Mars' present-day environmental conditions and produce liquid saline water (brine) (Clark 1978;Brass 1980;Clark and Van Hart 1981;Haberle et al 2001;Chevrier and Altheide 2008;Rennó et al 2009;McEwen et al 2011;Ojha et al 2015).…”