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- WASHINGTON - Signs of martian
snowfall, avalanches, "<link
- dust devils" and evidence for ancient oceans from
the <link Mars Global Surveyor
are profoundly changing how scientists perceive the Red Planet.
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- It's a far cry from the dry and dead world imagined by
previous generations.
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- "The Mars we thought we knew was not the real Mars,"
says Ken Edgett, a geologist with <http://barsoom.msss.com/ Malin Space
Science Systems of San Diego, California, which built the orbiter's cameras.
"I'm personally surprised."
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- Next month, scientists like Edgett will compare notes
at the annual Lunar and Planetary Institute conference in Houston.
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- But first they offered a tantalizing hint of their findings
at a session on Mars exploration at the <http://www.aaas.org/American
Association for the Advancement of Science's (AAAS) annual meeting February
18 in Washington.
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- Edgett, for example, has discovered the mystery behind
curious dark bands that crisscross the martian surface.
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- When he first saw them in 1998, he dubbed them "SUV
tracks," since they resembled the trail left by sport utility vehicles
on Earth.
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- Now he has found the real culprit -- dust devils, swirling
clouds of dust and wind that leave behind a dark streak. The dust devils,
which first were seen on Mars in the early 1970s on the <http://nssdc.gsfc.nasa.gov/planetary/viking.htmlViking
mission, apparently pick up lighter dust and deposit a darker material
underneath.
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- "It's pretty neat," Edgett said. "We caught
it in action."
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- "We have craters the size of the L.A. basin which
were filled up and then possibly exhumed." Ken Edgett, Geologist with
Malin Space Science Systems
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- The orbiter also sent back dramatic pictures of the rock
and soil layers of Mars' geology and photos of apparent avalanches on crater
lips that have occurred in the past two years. As well as evidence of massive
craters that seemed to have undergone profound changes.
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- "We have craters the size of the L.A. basin which
were filled up and then possibly exhumed," he said.
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- How this happened is still a mystery.
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- "This is not a Mars we can address with a camera.
We're going to have to send people," to understand the complex landscape,
he said.
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- David Smith, a researcher at NASA's Goddard Space Flight
Center in Greenbelt, Maryland, laid out a series of surprises for the AAAS.
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- His team, led by Massachusetts Institute of Technology
geologist Maria Zuber, measured the plains of northern Mars and found them
to be extraordinarily flat.
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- "It's as if from L.A. to Washington it is so flat
that there is only a deviation of 10 meters (32.8 feet)," he said.
"That is about as flat as can be."
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- Such data could provide important evidence that the northern
plains in at least some part of Mars' past were in fact oceans. The ocean
theory remains controversial, given that water on the surface of Mars today
would dissipate immediately into the thin atmosphere.
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- Smith,s team also found vivid detail of the strangely
contoured quality of the martian surface, with its highlands in the south
sloping dramatically to the plains below.
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- He noted that the <http://www.sci-ctr.edu.sg/mars/mgs/msss/camera/images/6_17_99_cracks/
Utopia basin in the northern plains -- barely visible to scientists until
recently -- reveals strange cracks that could be due to faulting, but also
resemble fissures found on Jupiter's frozen moon Europa.
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- Based on gravity data, the martian basin likely was once
an astonishing 7.45 miles (12 kilometers) deep, but was somehow filled
in over the centuries.
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- Data from the <http://www.space.com/space/marspix_803.html
poles, meanwhile, confirms that the ice is primarily water, but it is unclear
how long it has existed there.
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- These dark trails across a Martian plain -- spotted by
NASA's Mars Global Surveyor and dubbed SUV tracks -- puzzled researchers
until recently, when geologist Ken Edgett discovered that they mark the
path of dust devils.
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- Orbiter pictures show craters near the south pole filled
with ice -- almost as if the cap has retreated. It is similar to how a
retreating tide on Earth leaves puddles on a rocky coast.
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- The receding ice caps on Mars hint at a climatic warming
trend. If the caps melted, Smith said, they would cover the planet to a
depth of 29.5 feet (9 meters). If concentrated in one place like the northern
plains, "that would make a modest-sized ocean."
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- Another mystery is why the south polar cap, with its
thin layers of water ice, is slightly offset from the pole itself.
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- "It's something we don't understand," Smith
said.
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- What is clear is that clouds hover over the caps as the
weather starts to warm in the martian spring in the northern and southern
hemisphere.
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- Orbiter data shows that those thin clouds vanish as the
sun rises, and that the material falls back to Mars as frost or snow.
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- "This is clearly evidence that it snows on Mars,"
Smith said.
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