A new study shows that pockets of brine can form and persist from the equator to high latitudes on the Martian surface for a few percent of the year for up to six consecutive hours; however, they are not habitable because their water activities and temperatures fall outside the known tolerances for terrestrial life.
This image from ESA’s Mars Express shows a beautiful slice of the Red Planet from the northern polar cap downwards, and highlights cratered, pockmarked swathes of the Terra Sabaea and Arabia Terra regions. It comprises data gathered on June 17, 2019. This image was created using data from the nadir and color channels of Mars Express’ High Resolution Stereo Camera. The nadir channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface. North is up. Image credit: ESA / DLR / FU Berlin.
Due to Mars’ low temperatures and extremely dry conditions, a droplet of liquid water on its surface would instantly freeze, boil or evaporate, unless the droplet had dissolved salts in it.
This brine would have a lower freezing temperature and would evaporate more slowly than pure liquid water. Salts are found across Mars, so brines could form there.
“Our team looked at specific regions on Mars — areas where liquid water temperature and accessibility limits could possibly allow known terrestrial organisms to replicate — to understand if they could be habitable,” said co-author Dr. Alejandro Soto, a research scientist at the Southwest Research Institute.
“We used Martian climate information from both atmospheric models and spacecraft measurements.”
“We developed a model to predict where, when and for how long brines are stable on the surface and shallow subsurface of Mars.”
Distribution of (meta)stable brines on the Martian surface: (a, b) the total number of hours, in terms of percentage of the Martian year (shown in color), that a magnesium perchlorate (a) and calcium perchlorate (b) brine formed by deliquescence can exist on the Martian surface, as constrained by the MarsWRF predicted surface environment; areas where such brines cannot form and persist are shown as the background, gray-scaled shaded relief map based on Mars Orbiter Laser Altimeter (MOLA) data. The latitude range is restricted to non-polar regions. Image credit: Rivera-Valentín et al, doi: 10.1038/s41550-020-1080-9.
Martian hyper-arid conditions require lower temperatures to reach high relative humidities and tolerable water activities, which are measures of how easily the water content may be utilized for hydration.
The maximum brine temperature expected is minus 48.3 degrees Celsius (minus 55 degrees Fahrenheit) — at the boundary of the theoretical low temperature limit for life.
“Even extreme life on Earth has its limits, and we found that brine formation from some salts can lead to liquid water over 40% of the Martian surface but only seasonally, during 2% of the Martian year. This would preclude life as we know it,” Dr. Soto said.
While pure liquid water is unstable on the Martian surface, models showed that stable brines can form and persist from the equator to high latitudes on the surface of Mars for a few percent of the year for up to six hours. However, the temperatures are well below the lowest temperatures to support life.
“These new results reduce some of the risk of exploring the Red Planet while also contributing to future work on the potential for habitable conditions on Mars,” Dr. Soto said.
The study was published in the journal Nature Astronomy.
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E.G. Rivera-Valentín et al. Distribution and habitability of (meta)stable brines on present-day Mars. Nat Astron, published online May 11, 2020; doi: 10.1038/s41550-020-1080-9
