New findings from NASA's Mars Reconnaissance Orbiter (MRO) provide the strongest evidence yet that liquid water flows intermittently on present-day Mars. They have been seen to flow during the Martian summer and ebb during the Martian winter.
Lujendra Ojha, Mary Beth Wilhelm, Scott L. Murchie, Alfred S. McEwen, James J. Wray, Jennifer Hanley, Marion Massé & Matt Chojnacki. Spectral evidence for hydrated salts in recurring slope lineae on Mars AOP. Nature Geoscience, 2015; DOI: 10.1038/ngeo2546
Hydrated salts in solution with liquid water keep the water flowing even in sub-zero temperatures. Think of it as antifreeze. The spectral signatures are caused by hydrated minerals called perchlorates. The hydrated salts are consistent with the chemical signatures of a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate. Some perchlorates have been shown to keep liquids from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 Celsius). On Earth, naturally produced perchlorates are concentrated in deserts, and some types of perchlorates can be used as rocket propellant.
Perchlorates have previously been seen on Mars. NASA's Phoenix lander and Curiosity rover both found them in the planet's soil, and some scientists believe that the Viking missions in the 1970s measured signatures of these salts. However, this study of RSL detected perchlorates, now in hydrated form, in different areas than those explored by the landers. This also is the first time perchlorates have been identified from orbit.
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These results indicate that the presence of liquid water on the surface could potentially be exploited and used not only as propellant base, but for a far more permanent human presence on Mars.