When did water last flow on ?? ??Mars?
It's one of the most intriguing, looming questions in planetary science. Previous estimates suggest Mars has been a bone-dry desert, devoid of any water for some 3 billion years. But new research from Mars scientists suggests water flowed on the red planet 2 billion years ago, or 1 billion years later than researchers supposed.
This means Martian life — if any ever existed — could have had significantly more time to dwell, or evolve, on Mars' surface.
"Mars had habitats for longer than we thought," Bethany Ehlmann, a planetary scientist and the associate director of the Keck Institute for Space Studies at the California Institute of Technology, told Mashable. Ehlmann was a coauthor of the research, published on Jan. 27 in the journal AGU Advances.
"Mars had habitats for longer than we thought."
An excellent example of this evidence for water is shown in the image below, which was captured by NASA's satellite the Mars Reconnaissance Orbiter. The researchers looked at images of dried-up channels and depressions that contained big deposits of salt. These are the patchy white clumps seen in the channel. (The conspicuous crater to the right of the ancient waterway is about a mile wide.)
The salt deposits, Ehlmann explained, are downslope from higher elevations. It's strong evidence of water once melting from snow on slopes and hills (like it does on Earth) and then flowing down. "They had to come from snow and ice," Ehlmann said. The researchers found these salty mineral deposits in both shallow ponds and the winding channels that once fed these ponds.
An image from NASA's Mars Reconnaissance Orbiter shows salt deposits lying in a dried-out channel on Mars. Credit: NASA / JPL-Caltech / MSSS 
An artist's conception of the Mars Reconnaissance Orbiter above Mars. Credit: NASA To date these salty deposits, the researchers used well-known understandings of how long ago craters and volcanic lands formed on Mars. For example, if volcanic terrain formed some 2 billion years ago, then the salts collected on top must have flowed through after, providing an age estimate.
An earlier Mars satellite actually discovered these salts nearly 15 years ago. But the old discoveries have led to new, exciting insights about water on Mars.
SEE ALSO: The space race forged immortal rock and roll guitarsPlanetary scientists are confident Mars was once a world with blue, sprawling oceans, somewhat like Earth. What remains unknown is whether any life flourished in Mars' watery places. NASA's Perseverance rover is currently sleuthing out potential signs of past life in the planet's Jezero Crater, a place the space agency says was "once flooded with water and was home to an ancient river delta."
The Jezero Crater, however, likely held water some 3.5 billion years ago. This latest research contends Mars hosted water much later, perhaps considerably later than 2 billion years ago. Stay tuned. Ehlmann and her colleagues are on the water trail.
"Mars may have had small amounts of liquid water much more recently than we think," Ehlmann said. "The question is how recently."
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