[meteorite-list] Circumstantial Evidence For Water On Mars

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http://www.washingtonpost.com/national/health-science/water-on-mars-scientists-find-strongest-evidence-yet/2011/08/03/gIQAiYcWuI_story.html?hpid=z8



By Marc Kaufman, Published: August 4
For decades, space scientists have searched Mars for signs of water, the 
liquid generally believed to be essential for life. Now, they may well have 
found it.

Scientists announced Thursday that they had detected dozens of slopes across 
the southern hemisphere of the planet where previously undetected dark 
streaks come and go with the seasons. When the planet heats up, the streaks 
appear and expand downhill. When it gets cold, the streaks disappear.

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Scientists say the seasonal appearance of small dark lines on Mars may be 
melted, salty water running down slopes during the Martian summer. Five 
image sequences from the Newton crater and one from the Horowitz crater show 
the black lines appearing near the tops of slopes and then growing into 
scores of "streaks" that remain for months until the cold weather returns 
and they disappear. The images were taken over five years by the HiRISE 
camera aboard NASA's Mars Reconnaissance Orbiter, which circles Mars to 
photograph the planet. (Aug. 4)

The best explanation they have so far is that those dark, fingerlike streaks 
are a kind of salty water that is running on or just below the Martian 
surface. At one location - Newton Crater - they have counted as many as 
1,000 of these possible streams flowing down the slopes and into a basin.

It's a discovery that, if confirmed, would fundamentally change the 
understanding of Mars and would strongly support the widely held theory that 
the planet was once far more wet and warm. And scientists say the discovery 
of water would provide the best target yet for finding possible life beyond 
Earth.

"We haven't found any good way to explain what we're seeing without water," 
said Alfred Mc­Ewan of the University of Arizona's Lunar and Planetary 
Laboratory. McEwan is the lead author on a paper about the discovery in the 
journal Science.

"And if we confirm that it is a salty water, then we have the best idea yet 
about where to go to try to find extant life on Mars," McEwan said.

The dark streaks were initially noticed by a student at the school in images 
sent back by the Mars Reconnaissance Orbiter (MRO). The pixelated images 
were taken as far back as 2007, but with so much data coming in from space 
missions, they had remained unstudied. McEwan suggested that the student - 
geophysics junior Lujendra Ojha - examine over time the locations with 
streaks, and Ojha found that the streaks changed dramatically by season.

"None of these images by themselves are particularly revealing," McEwan 
said. "But when you put them together and see what happens over time, then 
you can clearly see something important is happening."

Gradually, a team of researchers determined that the changes came with 
increasing and decreasing temperatures. They began scouring the MRO images 
for other similar sequences and so far have found seven confirmed locations 
and possibly 32 more. In all cases, the flows appear to go around, rather 
than over, obstacles such as rocks, and sometimes they peter out before they 
reach flat ground. They are generally between about two feet and 15 feet 
wide, and occur during the Martian summer, when temperatures range from 10 
degrees below zero to 80 degrees Fahrenheit.

At a NASA news conference Thursday, McEwan and others associated with the 
MRO, Mars science and astrobiology hailed the finding as a potential turning 
point. Philip R. Christensen, a geophysicist at Arizona State University, 
said it constituted the best evidence for the possible existence of water on 
the Martian surface. Indiana University biogeochemist and astrobiologist 
Lisa Pratt said it also offered the most promising habitat discovered for 
current Martian life and speculated that the conditions could be similar to 
Siberian permafrost, where life exists. All of the speakers, however, said 
the finding was, at this point, circumstantial rather than proven.

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Phil Whitmer