- SAN FRANCISCO (AP) - Some scientists think Mars' north pole looks like a hockey
puck. Others liken it to an icy meringue.
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- Its frosty surface slopes as gently as
a beginner's ski run in some places, but it's also riddled with gorges
and cliffs; one trough plunges deeper than the Grand Canyon.
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- On one thing planetary scientists analyzing
the first close-up views of the top of Mars can agree: It looks like nothing
they've seen before.
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- "Similar features do not occur on
any glacial or polar terrain on Earth," said Maria Zuber of the Massachusetts
Institute of Technology.
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- Researchers discussed the new three-dimensional
images supplied by the Mars Global Surveyor spacecraft on Sunday at the
American Geophysical Union meeting here. More details on the Martian pole
will be published Friday in the journal Science.
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- It's the latest discovery in what is
now a two-year mission by the spacecraft to orbit the Red Planet and capture
images of its surface with a variety of instruments, providing detail that
is not available even for some locations on Earth.
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- The north pole images have left many
researchers intrigued, but perhaps a little disappointed.
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- It is made of water ice, which could
be a good omen for finding at least traces of ancient life somewhere on
the planet. But while the northern ice cap covers an area 50 percent greater
than Texas, researchers had expected it to be bigger.
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- Even with Mars' very cold climate, it
is only half the size of the ice cap covering Greenland and only 4 percent
of the Antarctica's combined ice sheets.
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- The amount of water trapped in the ice
cap is not sufficient to have carved the deep gullies that scar the surface
of the planet, and is about 10 times less than the minimum volume that
researchers believe would have been necessary to fill an ancient ocean.
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- It rests in a deep basin at the top of
the planet that might have been created by an asteroid impact similar to
craters on the Moon. The ice cap measures 750 miles and is 1.8 miles thick.
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- "It looks like a hockey puck in
a shallow depression," said David Smith of NASA-Goddard Space Flight
Center in Greenbelt, Md.
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- Mars Global Surveyor is gradually descending
into the Martian atmosphere using its own aerodynamic drag to slow down.
Since last summer it has made over 180 looping orbits around the planet's
poles, passing as close as 80 miles above the ice cap.
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- Carbon dioxide clouds over the ice cap
are likely to be composed of carbon condensed out of the frigid atmosphere
during the winter in the northern hemisphere, researchers said.
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- The new images raise more questions about
past conditions on Mars than they answer.
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- For example, how did the ice cap form?
Because the ice cap rests in a basin, it is likely that liquid water on
the planet's surface flowed north from the equator to the pole. If true,
it would mean that scientists must reconsider theories of the hydrologic
cycle on Mars.
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- Features apparent in other images of
Mars' northern hemisphere show evidence of ancient springs. These springs
may have supplied the additional water required to carve surface features.
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- "The springs apparently were fed
by groundwater," said Michael Carr of the U.S. Geological Survey.
"The amount of ice in the cap cannot possibly explain the features
that we see. I think the water is there now."
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- NASA plans to launch its next unmanned
satellite to study the Martian climate on Thursday. In January, the space
agency plans to launch another spacecraft to study the south pole of Mars.
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