Dark 100-metre-long streaks called recurring slope lineae, are seen flowing downhill on Mars. Scientists believe these are formed by seasonal water flow. This composite image depicts a processed, colour-enhanced view to better show low-contrast features. (C) NASA/JPL/University Of Arizona.
NEW YORK, US: Trickles of salt water may flow freely along ravines on Mars despite the planet’s extreme aridity, deep cold and tenuous atmosphere, scientists funded by the National Aeronautics and Space Administration (NASA) said Monday.
In a new satellite study, the scientists said their analysis of salt deposits detected in gullies on the red planet “strongly supports” the idea that rivulets of liquid brine periodically seep to the surface and stream down these Martian slopes, leaving distinctive streaks.
It is the most persuasive evidence yet that liquid water can be found today on the surface of Mars, experts said. The scientists published their research in the journal Nature Geoscience.
“This water is briny, not pure,” said planetary scientist Mary Beth Wilhelm at NASA’s Ames Research Center in Mountain View, Calif. “Our results may point to more habitable conditions on the near-surface of Mars than previously thought.”
For decades, planetary researchers have known that there is frozen water in the polar ice caps of Mars. Earlier this year, researchers using ground-based observatories concluded that Mars once had more water than in the Arctic Ocean on Earth. But that vast primitive ocean apparently vapourized billions of years ago.
Today, the planet’s landscape is a mosaic of dry deltas, ancient lake beds, stream sediments and river valleys that testify to the powerful effects of water long ago. Surface water in modern times—critical for conditions conducive to life and for supplying proposed human expeditions—so far has eluded detection.
In the latest study, scientists led by Lujendra Ojha at Georgia Institute of Technology used a spectrometer aboard the Mars Reconnaissance Orbiter to probe the chemistry of puzzling fingerlike ditches discovered on the planet four years ago.
Dark streaks in these gullies, each about a hundred yards long or so, show up during warm seasons, lengthen and then fade during cooler seasons, as if made by surface water streaming downhill. Ojha and his colleagues first studied them in 2011 with the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars, but they couldn’t find water, they reported at that time in Science.
By fine-tuning their data, they now have identified the chemical signature of salts that typically form in the presence of water—magnesium chlorate, magnesium perchlorate and sodium perchlorate. They tested gullies at four different locations around the planet.
There is “molecular water trapped inside the salt structure,” Ojha said. “This means these features are forming in contemporary liquid water.”
If true, those salts could help keep surface water liquid by lowering its freezing temperature and dramatically slowing its rate of evaporation, the researchers said. In warm months when the streaks form, the temperatures along these slopes normally range from about minus 23 degrees celsius up to about zero degrees—the freezing point of water.
Based on their orbital measurements, this surface water on Mars is far saltier than Earth’s seawater. “It will be much, much saltier than Earth’s oceans,” said University of Arizona researcher Alfred McEwen, principal investigator for the imager aboard the Mars orbiter used to take pictures of the gullies.
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