The dark streaks in this picture may be signs of salty water (Image: NASA/JPL/University of Arizona)
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IT鈥橲 a flow chart from another world. NASA鈥檚 Mars Reconnaissance Orbiter has found the best evidence yet that liquid water streams along the planet鈥檚 surface during warm seasons.
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Recurring slope lineae (RSL) 鈥� dark streaks that appear, grow and then fade each Martian year 鈥� were discovered in 2011, and appeared to signify flowing water. Now data from the orbiter鈥檚 spectrometer, which can help identify surface minerals, would appear to back that idea.
Spectral measurements from four RSL sites reveal the presence of hydrated salts 鈥� probably magnesium perchlorate, magnesium chlorate and sodium perchlorate 鈥� that can absorb water from the atmosphere and lower its freezing point, letting it stay liquid even in Mars鈥檚 cold climate (Nature Geoscience, ).
The Curiosity rover may be able to check out similar streaks, although the terrain may prevent it getting up close. Earlier this year, of the US Geological Survey and colleagues observed features resembling RSL in Gale crater, where Curiosity landed.
鈥淎ll of the activity that we鈥檝e seen has been on steep slopes that would be difficult for the rover to access, but Curiosity鈥檚 cameras will be able to watch for changes,鈥� Dundas says. Curiosity has already found evidence of perchlorates at Gale crater, as well as organic compounds.
Whether or not these damp flows could sustain life depends on how salty they are, says study co-author Lujendra Ojha of the Georgia Institute of Technology in Atlanta. Water saturated with salts would be hostile to life, but just a trace 鈥渟hould be fine鈥�.
But fellow team member Alfred McEwen of the University of Arizona, Tucson, is less sanguine. 鈥淚f I were a microbe on Mars, I wouldn鈥檛 live near one of these RSLs,鈥� he says. 鈥淲e think there is subsurface fresh water nearer the poles.鈥�
The find is likely to reignite debate over how to search for life on Mars, and even whether a search is worth it. Some astrobiologists criticised NASA when plans for its future Mars 2020 rover left out DNA sequencers and other instruments designed to look for living organisms.
But others think Mars is probably a dead world, and that it would be more fruitful to search in the subsurface oceans of Europa, one of Jupiter鈥檚 moons, or Enceladus, one of Saturn鈥檚.
This article appeared in print under the headline 鈥淪altwater streaks found on Mars鈥�