Thanks to seasonally warm temperatures and some iron-based anti-freeze.
NASA scientists have long chanted a mantra about Mars: follow the water, follow the water. So, we sent a lander to the northern latitudes looking for extant ice. More recently, the Mars Curiosity rover has been exploring planetary features that seem created by long-ago water flows, at least if Martian geology is as familiar as we think it is.
But what about water now ? Flowing water.
Georgia Tech scientists working with the Mars Reconnaissance Orbiter spotted some seasonal darkening along some slopes during warm weather. In the image below, the lines move from right to left down the slope of the Newton crater . They're called "recurring slope lineae."
It looks, to eyes on Earth, like some kind of water flow.
"We still don't have a smoking gun for existence of water in RSL, although we're not sure how this process would take place without water," the graduate student who discovered the RSL, Lujendra Ojha, said in a NASA release.
But temperatures on Mars are too cold for regular old H2O. The water would have to have some kind of natural anti-freeze in it. And that's what Ojha and Georgia Tech professor James Wray went looking for in new studies.
They found that iron concentrations increase in RSL regions as the lines get darker and longer. The scientists hypothesize that it's some kind of iron-based antifreeze flowing in the water, perhaps, they suggest, ferric sulfate.
In any case, these recent studies don't conclusively prove whether there is flowing water on Mars, nor do they begin to answer the big question: could this water support some sort of life? After all, it is the necessity of water for life as we know it that makes scouring Mars for water NASA's reasonable MO.
But it does make for an exciting time for Martian researchers: flowing water on Mars would be a very big deal.