Scientists have caught Mars crying salty tears.
Photos from NASA's Mars Reconnaissance Orbiter show dark streaks flowing down Martian slopes. The streaks appear in sunny spots or when the weather is warm, and they fade when the temperature drops.
Water was suspected to be involved, but now scientists have confirmed its presence. The new analysis, published in Nature Geoscience, shows salts mixed with water when the streaks are darkest. The water disappears when the streaks lighten.
"It's only when these streaks are biggest and widest that we see evidence for molecular water," says Lujendra Ojha, a graduate student at the Georgia Institute of Technology.
Ojha cautions this isn't the same as streams trickling downhill on Earth. Standing on the streaks would be like standing on a hot beach on Earth and dribbling a little water out of a drinking bottle. "You would just see a hint of wetness," he says.
Ojha says the water could be important for future exploration of Mars. It might be that astronauts could one day use it for everything from drinking water to rocket fuel, but that depends on how much there is.
The water could be coming from a subsurface reservoir, but that's not the only option, Ojha says. Ice, or even moisture in the atmosphere, could also be causing the streaks.
"We're not entirely sure what the source of the water may be," he says.
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NASA announced today that it has solved a mystery on Mars. NPR's Geoff Brumfiel has more on what scientists found and what it means for our understanding of the red planet.
GEOFF BRUMFIEL, BYLINE: Mars has these funny looking streaks on the slopes of its mountains and craters.
LUJENDRA OJHA: They look like if you would, like, take a pencil and if you would make a shade. They're very linear. They're very - they just look like a line on the surface flowing downhill.
BRUMFIEL: Lujendra Ojha is a graduate student at the Georgia Institute of Technology. For the past five years, he's been studying these lines with a satellite called the Mars Reconnaissance Orbiter, and he's noticed something. They're changing.
OJHA: They like to form when the surface of Mars is hottest, so they form in the summer.
BRUMFIEL: What's more, they don't form in the planet's frigid, shady spots.
OJHA: They sort of follow the sun. They always like to form on slopes that get the most amount of sunlight.
BRUMFIEL: The streaks appear in salt deposits. When the Mars weather is balmy, they grow, and the team can detect water molecules in the salts. But when it gets cold, the streaks shrink, and the water disappears.
OJHA: So it's only when these streaks on Mars are biggest and widest that we see this evidence for molecular water in these cells.
BRUMFIEL: Now, we're not talking rivers here. Ojha says this is more like splashing a bit of water out of a bottle onto a hot, sandy beach.
OJHA: On the surface, you would just see that hint of wetness.
BRUMFIEL: Mars had lots of water billions of years ago, but this is the first evidence for liquid water on modern-day Mars. Does that mean there's life today or that future astronauts will have plenty to drink if they ever go? Well, it depends.
OJHA: But we don't really have a good idea how much water is involved.
BRUMFIEL: There could be a lot of salty water underground, or it could be the salts on the surface are sucking up a bit of moisture out of the red planet's thin atmosphere. Either way, researchers are excited to find water at work on modern-day Mars. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.