Liquid Martian brines may be more common than once thought, but they are unlikely to play host to anything that looks like life as we know it, a paper in Nature Astronomy has found.
Stable liquid water is considered as one of the necessary ingredients for life to emerge, but under current Mars conditions, it is both too cold and its atmosphere too thin for it to last without freezing or subliming into vapour. But liquids containing high concentrations of salts can last much longer – longer than many thought, according to Edgard Rivera-Valentín, research scientist with the Universities Space Research Association at the Lunar and Planetary Institute, and his team.
After writing software using an experimentally validated thermodynamic model and a Martian climate model, with recalibrated environmental data from the Thermal and Electrical Conductivity Probe on the Phoenix lander (available on the NASA Planetary Data System Geosciences Node), the team looked into where these brines could form on Mars and for how long, and found they would be potentially "common," but extremely cold.
They postulated that up to 40 per cent of the Martian surface, at all latitudes down to the equator, could host stable brines. These brines could last for up to six consecutive hours on the surface, for up to 2 per cent of the entire Martian year.
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The authors also found that brines in the subsurface could last up to 10 per cent of the Martian year at a depth of 8cm. However, should their existence be confirmed, they would be "inhospitable for Earth's microorganisms" – and could "not sustain terrestrial life".
Martian brines attracted a wave of interest in 2018 when GeoScience published [PDF] research around the potential for aerobic life to draw "sufficient" O2 from any brines.
Evidence pointing to brines on Mars's surface has previously been surfaced. In 2015, Nature reported a study that used the Compact Reconnaissance Imaging Spectrometer for Mars instrument onboard the Mars Reconnaissance Orbiter examining from four different locations and found evidence for hydrated salts at all four locations.
Using an experimental approach on Earth, Rivera-Valentín and his colleagues used data modelling to show the presence of Mars brines may be much more common than thought.
Managing expectations of Mars explorers, they explained that only the lowest eutectic solutions can form, leading to brines with temperatures of less than 225 K (about -48˚C). "Our results indicate that (meta)stable brines on the Martian surface and its shallow subsurface (a few centimetres deep) are not habitable because their water activities and temperatures fall outside the known tolerances for terrestrial life," the paper explains.
The up-side here is that the brines cannot be classified as "Special Regions" according to Planetary Protection policies. This means that the places where these "stable brines" are found to exist could be targets for future Martian exploration, since they would limit the damage meatbag humans could potentially do to the Red Planet.
The authors note that the "risk of biological contamination from Earth is negligible". So, presuming we ever manage to send a crewed vehicle to the Red Planet, the lucky old Office of Planetary Protection and its international counterparts wouldn't need to build a sterile spacecraft for the purpose. ®