By Alex Dobuzinskis
LOS ANGELES (Reuters) - NASA scientists have discovered new evidence that briny water flows on Mars during its warmest months, raising chances that life could exist on the Red Planet, the space agency said on Thursday.
NASA first found signs of water on Mars more than a decade ago, but earlier indications were that any existing water would be frozen and concentrated at the poles.
Recently analyzed images from NASA's Mars Reconnaissance Orbiter satellite show dark, finger-like features that extend down some slopes and crater walls on the planet during its late spring through summer, fading in the Martian winter.
"This is the best evidence we have to date of a liquid water occurring today on Mars," said Philip Christensen, a geophysicist at Arizona State University, Tempe, in a NASA panel announcing the findings in Washington.
NASA scientists believe that if there is liquid water on Mars, it would be highly salty and lie beneath the surface. That would explain why it would not freeze in the planet's frigid surface temperatures, which can fall to around 200 degrees below zero Fahrenheit (minus 128 degrees Celsius), or evaporate in its low air pressure.
"It is more like a syrup, maybe, in how it flows," said Alfred McEwen of the University of Arizona, Tucson, principal investigator in charge of a special camera on the Mars orbiter called a High Resolution Imaging Science Experiment.
He also is the lead author of a report on evidence of water flows published on Thursday in the journal Science.
BETTER THAN ICE
The scientists on NASA's panel stressed that liquid water is more likely to sustain life than ice, underscoring the importance of the latest discovery.
Past NASA discoveries revealed evidence of ancient shorelines and riverbanks on Mars. And analysis of gullies on the Red Planet five years ago turned up fresh mineral deposits that suggested recent water flows, but provided no categorical proof of that, scientists said.
The latest discovery is more difficult to explain away as evidence of anything but contemporary water flows, said Michael Meyer, Mars exploration program lead scientist at NASA.
Another possibility to account for the periodic darkening in the areas under examination is dust moving along the surface of the planet, McEwen said. But dust avalanches would occur at more random intervals, rather than on a seasonal basis, he said.
Scientists on the panel said the latest imaging evidence of flowing water also suggests the existence of liquid water closer to the planet's equator than previously found.
Any liquid water would likely lie beneath the surface because the atmosphere on Mars is so thin that liquid water above ground would quickly evaporate, scientists said.
Some organisms on Earth thrive underground with little access to sunlight, and the same thing could be occurring on Mars, said Lisa Pratt, biogeochemist at Indiana University, Bloomington, and a participant on the NASA panel discussing the results on Thursday.
Pratt said further research is needed at the seven sites where recurring evidence of flowing water was found.
"It is our first chance to see an environment on Mars that might allow for the expression of an active biological process, if there is present-day life on Mars," she said.
(Reporting by Alex Dobuzinskis; Editing by Steve Gorman, Jerry Norton and Xavier Briand)