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Trickles on Mars look like sand, not water

Recurring slope lineae
Recurring slope lineae appear as dark streaks in this picture from the HiRISE camera on NASA’s Mars Reconnaissance Orbiter. (NASA / JPL / Univ. of Arizona / Lujendra Ojha et al. / Geophysical Research Letters)

Scientists have long been intrigued by what seem to be wet streaks that appear on the slopes of Martian craters in warm weather, and disappear in winter. Now a research team reports that the best explanation is that they’re not wet streaks at all, but streaks of dust and sand.

The findings, published today in Nature Geoscience, are likely to disappoint those who hoped that the features known as recurring slope lineae, or RSLs, point to sources of liquid water beneath the Red Planet’s surface.

“This new understanding of RSL supports other evidence that shows that Mars today is very dry,” study lead author Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center said in a news release.

Some astrobiologists had hoped that the areas around the RSLs just might harbor subsurface life. That’s why NASA has said the thousands of potential RSL sites, including a smattering of prospects near the Curiosity rover, should be off-limits for the time being due to concerns about contamination.

The report in Nature Geoscience is based on an analysis of 151 streaky features at 10 sites. Nearly all of the streaks appear on slopes that are steeper than 27 degrees, which would be consistent with the behavior of tumbling sand. If the streaks were caused by water seeping from the subsurface, they should be seen on slopes that are less steep, the researchers say.

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By Alan Boyle

Mastermind of Cosmic Log, contributing editor at GeekWire, author of "The Case for Pluto: How a Little Planet Made a Big Difference," president of the Council for the Advancement of Science Writing. Check out "About Alan Boyle" for more fun facts.

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