We finally have a firm answer to one of the biggest mysteries of Mars. Not only did the Red Planet have water in the past, but it has it right now, flowing in a briny mix that keeps it in a liquid state. This confirms decades of observations.

In an article published in Nature Geoscience, a team led by Lujendra Ojha of the Georgia Institute of Technology confirms that seasonal flows in mountainous regions of the planet correspond with the presence of briny water. The seasonal flows were first noticed in 2010, with water the strongest suspect. Spectral observations of season data from the Mars Reconnaissance Orbiter indicate the presence of hydrated salts on the surface, or water mixing with a thick brine of salts.

"It's unambiguous evidence that liquid water is flowing on Mars."

However, the observations don't have a "smoking gun" as to how the flows occur. Some of the hypotheses include an underground aquifer, accumulations of humidity, or possible seasonal melting, though there is a counter for each. (Like an aquifer extending into mountainous regions, possible lack of sufficient humidity, or lack of regional surface ices, respectively.) The team also is working under the idea that it could be a mix of all of these.

"It's quite possible that on different parts of mars, they're forming through different mechanisms," Ojha said in a phone interview.

These dark, narrow, 100 meter-long streaks called recurring slope lineae flowing downhill on Mars are inferred to have been formed by contemporary flowing water. NASA/JPL/University of Arizona

What's for sure: this isn't typical water. Instead, it's a briny mixture called hydrated salts that move a little more like a fluid than like a liquid. They also only occur seasonally, having not been seen when Mars is in its winter months. The salts allow the water to stay liquid at temperatures down to around -60 degrees Fahrenheit.

This also confirms the origin of perchlorates, aerosol salts found on the surface of Mars as far back as the Viking landers. While liquid water (past or present) has always been a suspect, this could be evidence that it's from some combination of ancient and modern flows.

"It's unambiguous evidence that liquid water is flowing on Mars," Ojha says.

Dark narrow streaks called recurring slope lineae emanating out of the walls of Garni crater on Mars. NASA/JPL/University of Arizona

Of course, the question will come up: what does this mean for life on Mars? It's an incremental process to find it, first determining whether the conditions are right for it, then determining further if it's present. All Ojha says is that if there is life currently on the surface, these conditions would be the place to look.

NASA/JPL/University of Arizona

"All we can assert is that the places where we see these aerosols are more habitable than other places we've looked in the past," he says. "We're just scratching the surface. It's too premature for us to say anything, but it provides us a great place to study."

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