Those dark streaks cascading down the Martian landscape may not be caused by flowing water after all

Those dark streaks cascading down the Martian landscape may not be caused by flowing water after all

If you’re among the many who did somersaults in 2015 when NASA announced it had found “the best evidence yet” for water flowing on the surface of Mars, you’ll probably want to sit down. 

On Monday, a team of researchers from the U.S. Geological Survey published a study that suggests dark streaks spotted on the steep slopes of Mars probably aren’t moist patches that could harbor microbial life, but instead are left behind by flowing sand or dust.

The finding comes as a disappointment to scientists who had pointed to the “recurring slope lineae,” as they’re known, as a strong indicator for liquid water below the planet’s surface.

“This new understanding . . . supports other evidence that shows that Mars today is very dry,” lead author Colin Dundas said in a news release.

The study, published in the journal Nature Geoscience, is based on observations made by the Mars Reconnaissance Orbiter’s HiRISE camera. The new work rolls back earlier findings that the dark streaks were likely caused by liquid salty water that flowed when the seasons and temperatures were just right. U.S.G.S. scientists were joined in making the new analysis by researchers from the Planetary Science Institute, the University of Arizona, and Durham University in England.

“We’ve shown that RSL are likely granular flows, which changes our assessment of what they mean for flowing liquid water on Mars and points to formation processes with little or no liquid,” wrote Dundas in an email.

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