- WASHINGTON (Reuters) - Life
on Mars might lurk in long gullies carved by liquid water underneath a
dirty but protective blanket of snow, astronomers said on Wednesday.
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- Astronomers first observed the Martian gullies three
years ago, but did not know what created them. Philip Christensen, a professor
at Arizona State University, has now analyzed images from NASA's Mars Odyssey
spacecraft and said they may have been gouged out by melting snow.
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- "I think we have discovered remnants of snowpacks
on Mars that in the recent past have melted," Christensen said at
a briefing at NASA headquarters.
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- "I think if you were to land on one of those and
stick a shovel in the ground, you'd be shoveling snow," he said. "And
if life ever existed on Mars, I can't think of a more exciting place to
possibly go and look."
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- In Christensen's scenario, the upper layer of snow is
loaded with dust and is therefore less easily melted than snow without
those impurities. Only a few inches (cm) beneath that snowpack, a lower
layer of snow can melt without evaporating.
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- It forms the gullies at the edges of craters on Mars,
much as snow-melt might form gullies on earthly mountainsides. The gullies
Christensen's team observed were in the mid-latitudes of Mars, rather than
at the poles, which is where other astronomers have focused the search
for water.
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- The quest for liquid water on Mars is a long-standing
one, because water is seen as a prerequisite for life as it is known on
Earth.
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- Christensen said the snowbelts in the Martian mid-latitudes
were active features, melting away and then returning over a cycle of 100,000
years or so. At this point, there are what look like snow fields in addition
to the gullies.
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- "It points to a very dynamic, active Mars,"
he said.
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- Lynn Rothschild, an expert on ecosystems at NASA's Ames
Research Center in California, said the new research, if proven, would
expand the range of possible habitats for life on Mars.
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- Noting that Earth-type life can exist in such seemingly
hostile environments as the Antarctic and in super-hot undersea vents,
Rothschild said some algae on Earth could exist in communities within snow.
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- In the Rocky Mountains and the Sierras, she said, such
algae can be so densely packed that it tints the snowy environment red,
producing what is known as "watermelon snow."
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- In a resting state, those organisms can survive for long
periods, "maybe like you see in Mars between the times that it snows,"
Rothschild said. "That's something that you could envision surviving
in the sort of conditions you describe."
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- She said the temperature range on Mars was within the
range that had been known to be habitable to some forms of life on Earth.
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- Images of the Martian gullies are available online at
http://photojournal.jpl.nasa.gov/catalog/PIA04408 and http://photojournal.jpl.nasa.gov/catalog/PIA04409.
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