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 McÂEwan 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
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