Brines on Mars not habitable, study says

Liquid brines on Mars may be more common and longer lasting than previously thought, but their properties and temperatures make them inhospitable for Earth’s microorganisms, according to a paper published in the journal Nature Astronomy. 

And that means, the authors say, that they cannot be classified as Special Regions according to Planetary Protection policies.  

Special Regions are defined as environments able to host liquid water that simultaneously meets certain temperature and water activity requirements that allow known terrestrial organisms to replicate.

Stable liquid water can’t persist on the surface of Mars, as the planet’s atmosphere is too thin and cold, but it was known that the presence of salts can create liquid substances, like brines, which can last stably for some time. 

To paint a clearer picture, Edgard Rivera-Valentín, from the Universities Space Research Association, Texas, Vincent Chevrier, from the University of Arkansas, and colleagues combined a thermodynamic model with a climate model to investigate where brines could form on Mars and for how long. 

“Our results show that metastability expands the locations and duration of brines on Mars, beyond what was previously thought, by including some equatorial regions,” they write.

They found, in fact, that up to 40% of the Martian surface at all latitudes down to the equator could host stable brines, and that these brines could last for up to six consecutive hours and during up to 2% of the entire Martian year. 

Brines in the subsurface could last up to 10% of the Martian year at a depth of eight centimetres.

The locations of the stable brines could be targets for future Martian exploration, the authors note, since the risk of biological contamination from Earth is negligible. But they aren’t officially “special”.

“This is because of the hyper-arid conditions of Mars, which require lower temperatures to reach high relative humidities and tolerable water activities,” the paper says. 

The Royal Institution of Australia has an education resource based on this article. You can access it here.

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