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Mystery Solved: Water DOES Flow on Mars

Scientists have their first evidence that trickles of liquid water play a role in sculpting mysterious dark streaks that appear during summertime months on Mars.

Scientists have their first evidence that trickles of liquid water play a role in sculpting mysterious dark streaks that appear during summertime months on Mars, a finding that has implications for potential life on Mars, as well as planning for future human expeditions.

The discovery, reported Monday in the journal Nature Geoscience, follows years of speculation and studies to learn why the faces of some cliff walls on Mars are streaked with narrow dark slopes, some more than 300 feet long, that appear when temperatures are warm and then vanish during the winter chill.

PHOTOS: Curiosity Snaps Selfies, Begins Mars Rock Drill

The streaks, known as recurring slope lineae, or RSL, were first reported in 2011 in the Martian southern highlands, but have since been found throughout the planet's equatorial region, particularly within deep canyons.

Using data collected by NASA's Mars Reconnaissance Orbiter and a new analysis technique, scientists were for the first time able to detect the telltale chemical fingerprints of hydrated salts in dozens of RSL sites.

"That implies that there was liquid water there very recently to leave this residue of hydrated salts. It confirms that water is playing a role in these features," University of Arizona planetary geologist Alfred McEwen told Discovery News.

In a press conference advisory, NASA said that the research "solves" a Mars mystery, but it actually opens the door to another, potentially more challenging puzzle: Where is the water coming from?

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"We haven't been able to pinpoint the source," lead researcher Lujendra Ojha, a graduate student at Georgia Institute of Technology, told Discovery News.

"Water could form by the surface/subsurface melting of ice, but the presence of near-surface ice at equatorial latitudes is highly unlikely," Ojha and colleagues write in Nature Geoscience.

Another option is that salts absorb water vapor directly from the Martian air, though scientists are at a loss to explain how they could trap enough water from the tiny amount available in the atmosphere to seep down hill slopes and form the streaks.

"It's just not clear that the atmosphere can supply enough water to do that," McEwen said.

Whatever the source of the water, its seasonal appearance on the surface of Mars raises the prospect that life might be present on the planet today.

NEWS: Is Mars Humid Enough to Support Life?

Scientists, however, are quick to note that the RSL water is briny and possibly so dense that no terrestrial organisms, at least, could survive there.

NASA, which is working toward a human expedition to Mars in the 2030s, has another interest in the water. Future crews will need water for drinking and to produce oxygen, both for breathing and for rocket fuel.

For now, far more information is needed about the chemistry of the water as well as its source.

"We're just starting to scratch the surface," Ojha said.

Palikir Crater, located inside Newton crater, contains thousands of individual flows called recurring slope lineae -- possible evidence of seasonal flows of liquid water on the surface of Mars.

Nearly one (Earth) year ago, NASA's Curiosity rover arrived at Mount Sharp, the key science destination of its mission. The rover has now spent three Earth years on the Red Planet, looking at rocks and environment to try to piece together the ancient past of Mars. Was it habitable for life? If so, did the life disappear? Why did the conditions change? These are all questions investigators are trying to learn the answers to. In this brief rundown of the science being done on Mount Sharp (officially known as Aeolis Mons), we've picked out some of the most intriguing and, frankly, beautiful photos of Curiosity's mountain.

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After extensive practice taking pictures of the rover, Curiosity's "selfies" are getting pretty amazing.

This is one of the latest ones

from Curiosity, showing it perched at the Marias Pass just after doing some drilling. While the selfies are used as a public relations tool, NASA also uses these pictures to monitor the condition of the rover in the harsh Martian environment. One thing the agency

is keeping an eye on is wheel damage

, for example.

Yep, that's a rock -- there are a lot of those on Mars. But look more closely at each one, and they reveal surprises. This particular rock is

embedded with silica

, a silicon-oxygen rock-forming compound that often shows up on Earth as quartz. It's an unusual find for Mars, and the team said it is going to take a closer look to see if it could preserve organic materials. Organics are considered building blocks of life, but not necessarily signs of life itself.

MORE: NASA's Curiosity Rover Eyes Weird Rock on Mars

Curiosity has a laser on board (called the Chemistry and Camera or ChemCam instrument) that shoots at rocks to figure out what they are made of. But for months, the auto-focuser malfunctioned and required multiple laser shots to be sent, slowing down the science. This image shows the result

after a successful software update

that takes several images and figures out how to target the focuser from there.

MORE: Sparks Fly as Curiosity Laser Blasts Mars Rock

In 28 pictures stitched together, Curiosity uncovered

an extensive network of mineral veins

at a site investigators dubbed "Garden City." These veins are created when a liquid cuts through cracks in a rock and leaves minerals behind. At the time this picture was taken, NASA was trying to figure out what the fluids were made of, and how the rock changed after the fluids touched it. It's all part of better understanding the ancient wet past on Mars and prospects for life.

MORE: Curiosity Has Hit a Martian Mineral Jackpot

Sometimes you can't predict what will happen when you do science. In this case, Curiosity's drill did a test to see if this "Mojave" rock could be suitable to collect a sample...

and the rock shattered

. While it wasn't a total surprise that the rock broke, what made this test interesting was it

created a few rock chips

. This gave Curiosity an opportunity to look at what a new rock looks like before it gets all weathered by Martian wind and elements.

MORE: Robot Smash! Curiosity Shatters Mars Rock Slab

In December, couple of building blocks of life came to light: Curiosity saw a

10-fold spike and fall in methane

around this time, and

detected carbon-bearing organic molecules on Mars

. While neither of these are necessarily signs of life, they point to conditions that could have been friendly for life at some point. Also, Curiosity got to flex its drill at the "Cumberland" rock target, which was a good thing as

a NASA senior review said the drill wasn't being used enough

(making it hard to justify the cost and complication).

MORE: Mars Mission Will Drill Deep for Inside Information

The very first hole

that Curiosity created in Mount Sharp revealed something exciting: the mineral it found was the same as one seen from orbit in the same region. Specifically, the rover

found evidence of hematite

, an iron oxide mineral that can precipitate out of water. Hematite was noted as a mineral of interest when the Curiosity landing site was being selected in 2010.

Image: Curiosity's path during the first few weeks at Mount Sharp in fall (Earth's northern hemisphere fall) 2014.

MORE: Curiosity Finds Tantalizing Mineral Clues for Mars Habitability