- Newly seen details in a fan-shaped apron of debris on
Mars may help settle a decades-long debate about whether the planet had
long-lasting rivers instead of just brief, intense floods.
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- Pictures from NASA's Mars Global Surveyor orbiter show
eroded ancient deposits of transported sediment long since hardened into
interweaving, curved ridges of layered rock. Scientists interpret some
of the curves as traces of ancient meanders made in a sedimentary fan as
flowing water changed its course over time.
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- "Meanders are key, unequivocal evidence that some
valleys on early Mars held persistent flows of water over considerable
periods of time," said Dr. Michael Malin of Malin Space Science Systems,
San Diego, which supplied and operates the spacecraft's Mars Orbiter Camera.
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- "The shape of the fan and the pattern of inverted
channels in it suggest it may have been a real delta, a deposit made where
a river enters a body of water," he said. "If so, it would be
the strongest indicator yet Mars once had lakes."
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- Malin and Dr. Ken Edgett, also of Malin Space Science
Systems, have published pictures and analysis of the landform in today's
online edition of Science Express. The images with captions are available
online from the Mars Orbiter Camera team, at and from NASA's Jet Propulsion
Laboratory, Pasadena, Calif., at http://photojournal.jpl.nasa.gov/catalog/PIA04869.
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- The fan covers an area about 13 kilometers (8 miles)
long and 11 kilometers (7 miles) wide in an unnamed southern hemisphere
crater downslope from a large network of channels that apparently drained
into it billions of years ago.
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- "This latest discovery by the intrepid Mars Global
Surveyor is our first definitive evidence of persistent surface water,"
commented Dr. Jim Garvin, NASA's Lead Scientist for Mars Exploration, NASA
Headquarters, Washington, D.C. "It reaffirms we are on the right pathway
for searching the record of martian landscapes and eventually rocks for
the record of habitats. Such localities may serve as key landing sites
for future missions, such as the Mars Science Laboratory in 2009,"
continued Garvin. "These astounding findings suggest that "following
the water" with Mars Global Surveyor, Mars Odyssey, and soon with
the Mars Exploration Rovers, is a powerful approach that will ultimately
allow us to understand the history of habitats on the red planet."
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- No liquid water has been detected on Mars, although one
of the previous major discoveries from Mars Global Surveyor pictures suggests
that some gullies have been cut in geologically recent times by the flow
of ephemeral liquid water. Another NASA orbiter, Mars Odyssey, has discovered
extensive deposits of near-surface ice at high latitudes. Mars' atmosphere
is now so thin that, over most of the planet, any liquid water at the surface
would rapidly evaporate or freeze, so evidence of persistent surface water
in the past is also evidence for a more clement past climate.
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- Malin and Edgett estimate that the volume of material
in the delta-like fan is about one-fourth the volume of what was removed
by the cutting of the upstream channels. Their analysis draws on information
from Mars Global Surveyor's laser altimeter and from cameras on Mars Odyssey
and NASA's Viking Orbiter, as well as images from the Mars Orbiter Camera.
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- "Because the debris in this fan is now cemented,
it shows that some sedimentary rocks on Mars were deposited by water,"
Edgett said. "This has been suspected, but never so clearly demonstrated
before."
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- The camera on Mars Global Surveyor has returned more
than 155,000 pictures since the spacecraft began orbiting Mars on Sept.
12, 1997. Still, its high-resolution images cover only about three percent
of the planet's surface. Information about Mars Global Surveyor is available
on the Internet at <http://mars.jpl.nasa.gov/mgs>http://mars.jpl.nasa.gov/mgs.
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- JPL, a division of the California Institute of Technology,
Pasadena, manages Mars Global Surveyor for NASA's Office of Space Science
in Washington. JPL's industrial partner is Lockheed Martin Space Systems,
Denver, which developed and operates the spacecraft. Malin Space Science
Systems and the California Institute of Technology built the Mars Orbiter
Camera. Malin Space Science Systems operates the camera from facilities
in San Diego.
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- This story has been adapted from a news release issued
by NASA/Jet Propulsion Laboratory.
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- http://www.sciencedaily.com/releases/2003/11/031114071532.htm
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