Signs of Liquid Water Found on Surface of Mars, Study Says

Despite its reputation as a forebodingly dusty, desolate and lifeless place, Mars seems to be a little bit wet even today.
Scientists reported on Monday definitive signs of liquid water on the surface of present-day Mars, a finding that will fuel speculation that life, if it ever arose there, could persist to now.

“This, I think, gives a focus of where we should look more closely,” said Alfred S. McEwen, a professor of planetary geology at the University of Arizona and the principal investigator of images from a high-resolution camera on NASA’s Mars Reconnaissance Orbiter.

In a paper published in the journal Nature Geoscience, Dr. McEwen and other scientists identified waterlogged molecules — salts of a type known as perchlorates — in readings from orbit.

“That’s a direct detection of water in the form of hydration of salts,” Dr. McEwen said. “There pretty much has to have been liquid water recently present to produce the hydrated salt.”

Though young Mars was inundated by rivers, lakes and maybe even an ocean a few billion years ago, the modern moisture is modest. Scientists have long known that large amounts of water remain — but frozen solid in the polar ice caps. There have been fleeting hints of recent liquid water, like fresh-looking gullies, but none have proved convincing.
In 2011, Dr. McEwen and colleagues discovered in photographs from the Mars Reconnaissance Orbiter dark streaks descending along slopes of craters, canyons and mountains. The streaks lengthened during summer, faded as temperatures cooled, then reappeared the next year.

They named the streaks recurrent slope linae, or R.S.L.s, and many thousands of them have now been spotted. “It’s really surprisingly extensive,” Dr. McEwen said.

Scientists suspected that water played a critical role in the phenomenon, perhaps similar to the way concrete darkens when wet, with no change in the shape of the surface, and returns to its original color when dry.

But that was just an educated guess.

Lujendra Ojha, a graduate student at the Georgia Institute of Technology, turned to another instrument on the orbiter that identifies types of molecules by which colors of light they absorb. But this instrument, a spectrometer, is not as sharp as the camera, making it hard to zoom in on readings from the narrow R.S.L.s.

“We had to come up with new techniques and novel ways to do analysis of the chemical signature,” said Mr. Ojha, the lead author of the Nature Geoscience article.

The researchers were able to identify the telltale sign of a hydrated salt at four locations. In addition, the signs of the salt disappeared when the streaks faded. “It’s very definitive there is some sort of liquid water,” Mr. Ojha said.
The perchlorate salts lower the freezing temperature, and the water remains liquid. The average temperature of Mars is about minus 70 degrees Fahrenheit, but summer days near the Equator can reach an almost balmy 70.
Many mysteries remain. For one, scientists do not know where the water is coming from.

“There are two basic origins for the water: from above or from below,” Dr. McEwen said. The perchlorates could be acting like a sponge, absorbing moisture out of the air, but measurements indicate very low humidity on Mars — only enough for 10 microns, or about 1/2,500th of an inch, of rain across the planet if all of the wetness were wrung out of the air.

That idea cannot be entirely ruled out if the lower part of the atmosphere turns out more humid than currently thought.

More at:

http://www.nytimes.com/2015/09/29/science/space/mars-life-liquid-water.html


Wonder what else they will find?