A new study casts doubt on the widespread interpretation that seasonal dark streaks on Martian dunes are caused by water.
Mars photos show an interesting landscape feature: dark streaks that appear to show flowing movement, which some thought may be water.
And Colin, along with his team, examined dozens of different images of the streaks - called recurring slope lineae or RSL - and determined that they didn't behave like running water.
NASA announced two years ago odd dark streaks on Mars might be formed by liquid water. The fact that these streaks only show up in places where there are steep slopes help highlight the fact that they're probably made of dry material.
However, while there is water on Mars - existing on the polar caps, ground ice, as well as in frosts and hydrated minerals - the evidence suggesting larger volumes of liquid water is ambiguous, according to researchers from the US Geological Survey.
The findings published today in Nature Geoscience argue against the presence of enough liquid water for microbial life to thrive at these sites.
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Thousands of RSL have been found on Mars, previously thought to be evidence of unexpected liquid water or brine flow. On Earth, only seeping water is known to have these behaviours, but how they form in the dry Martian environment remains unclear.
There are still unanswered questions, such as why the streaks appear and vanish with the seasons, and what makes them dark in color.
"This new understanding of RSL supports other evidence that shows that Mars today is very dry".
At a news conference that year, NASA's director of planetary science declared: "Liquid water has been found on Mars".
"Full understanding of RSL is likely to depend upon on-site investigation of these features", said MRO Project Scientist Rich Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California. That's bad news for people hoping to find conditions suitable for microbial life. RSL do still have some unusual features though, like their seasonal appearance and gradual growth, which we can't yet explain.