Communications of the ACM
Scientists Modeled Mars Climate to Understand Habitability
Climate models show that hydrated salts or brines like the dark streaks shown here are too cold to support life on Mars.
Credit: NASA / JPL-Caltech / Univ. of Arizona
A Southwest Research Institute scientist modeled the atmosphere of Mars to help determine that salty pockets of water present on the Red Planet are likely not habitable by extant Earth life forms. A team that also included scientists from Universities Space Research Association (USRA) and the University of Arkansas helped allay planetary protection concerns about contaminating potential Martian ecosystems.
The results are described in "Distribution and Habitability of (Meta)stable Brines on Present-Day Mars," published in Nature Astronomy.
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," says Alejandro Soto, a Southwest Research Institute senior research scientist and co-author of the study. "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."
Mars' 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 -55 F — 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," Soto says. "This would preclude life as we know it."
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 consecutive hours, a broader range than previously thought. 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," Soto says.
Co-authors of the Nature Astronomy study are Edgard G. Rivera-Valentín, with the Lunar and Planetary Institute, Universities Space Research Association, Vincent F. Chevrier, with the Arkansas Center for Space and Planetary Sciences, University of Arkansas, and Germán Martínez, with the Lunar and Planetary Institute, and the Department of Climate and Space Sciences and Engineering, University of Michigan. The SwRI portion of this research was funded by NASA under the Habitable Worlds program through a grant led by USRA.
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