Terrestrial life unlikely to contaminate Mars

Katie Ramirez
May 14, 2020

The model suggests that approximately 40 % of the Red Planet could support liquid brines for up to 5 hours at a time.

While fictional, the plot explores a very real and longstanding concern shared by NASA and world governments: that spacefaring humans, or our robotic emissaries, may unwittingly contaminate Earth with extraterrestrial life or else biologically pollute other planets we visit.

But she can go and the liquid - due to the dissolved salts.

A wide range of salts have been detected on Mars, with carbonate and sulfate salts being the most abundant. However, super-salty water, commonly known as brines, presents lower freezing points, being likely to resist more, regardless of the changing atmospheric conditions, from freezing cold temperatures to boiling hot degrees.

Liquid fresh water can't exist for long on the frigid Martian surface; the stuff quickly freezes or boils away into the planet's thin atmosphere.

One such study by Eriita Jones at the University of South Australia is in agreement with this suggestion. Scientists have been exploring Mars to find possible signs of life and to see if it could support new organisms in the future.

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The results indicate that 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 close subsurface could be wetter still: the model indicates that brines could be present during 10 % of the Martian year at a distance of nearly 8 centimeters. And its temperature will be about minus 48 degrees Celsius, which is nearly two times below the permissible values for life on Earth. This is contrast to studies such as those by Jones who advocate more favourable life sustaining conditions in the salty solutions.

Because saltwater is liquid at lower temperatures than pure water, an SwRI scientist modeled the climate of Mars to understand if pockets of brine on its surface could harbor life.

In the hyperarid conditions of Mars, coupled with its crippling freezing temperatures, it is just too much for microorganisms to survive, argue the authors and as such it means these brines can not be classified as "Special Regions" according to Planetary Protection policies, as they can not sustain terrestrial life.

Reference: "Distribution and habitability of (meta) stable brines on present-day Mars" by Edgard G. Rivera-Valentín, Vincent F. Chevrier, Alejandro Soto and Germán Martínez, 11 May 2020, Nature Astronomy.

If Martian brines are completely uninhabitable though, these restrictions could be loosened.

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