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NASA's Spirit rover has found a patch of bright-toned soil so rich in silica that scientists propose water must have been involved in concentrating it. Image Credit: NASA/JPL-Caltech/Cornell Larger view
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A patch of Martian soil analyzed by NASA's rover
Spirit is so rich in silica that it may provide some of the strongest
evidence yet that ancient Mars was much wetter than it is now. The
processes that could have produced such a concentrated deposit of
silica require the presence of water.
Members of the rover science team heard from a colleague during a
recent teleconference that the alpha particle X-ray spectrometer, a
chemical analyzer at the end of Spirit's arm, had measured a
composition of about 90 percent pure silica for this soil.
"You could hear people gasp in astonishment, " said Steve Squyres of
Cornell University, Ithaca, N.Y., principal investigator for the Mars
rovers' science instruments. "This is a remarkable discovery. And the
fact that we found something this new and different after nearly
1, 200 days on Mars makes it even more remarkable. It makes you wonder
what else is still out there."
Spirit's miniature thermal emission spectrometer observed the patch,
and Steve Ruff of Arizona State University, Tempe, noticed that its
spectrum showed a high silica content. The team has laid out plans
for further study of the soil patch and surrounding deposits.
Exploring a low range of hills inside a Connecticut-sized basin named
Gusev Crater, Spirit had previously found other indicators of
long-ago water at the site, such as patches of water-bearing,
sulfur-rich soil; alteration of minerals; and evidence of explosive
volcanism.
"This is some of the best evidence Spirit has found for water at
Gusev, " said Albert Yen, a geochemist at NASA's Jet Propulsion
Laboratory, Pasadena, Calif. One possible origin for the silica could
have been interaction of soil with acid vapors produced by volcanic
activity in the presence of water. Another could have been from water
in a hot spring environment. The latest discovery adds compelling new
evidence for ancient conditions that might have been favorable for
life, according to members of the rover science team.
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Spirit has found a patch of bright-toned, silicate-rich soil. Image Credit: NASA/JPL-Caltech/Cornell. Larger view
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David Des Marais, an astrobiologist at NASA's Ames Research Center,
Moffett Field, Calif., said, "What's so exciting is that this could
tell us about environments that have similarities to places on Earth
that are clement for organisms."
Spirit and its twin rover Opportunity completed their original
three-month prime missions in April 2004. Both are still operating,
though showing signs of age. One of Spirit's six wheels no longer
rotates, so it leaves a deep track as it drags through soil. That
churning has exposed several patches of bright soil, leading to some
of Spirit's biggest discoveries at Gusev, including this recent
discovery.
Doug McCuistion, director of NASA's Mars Exploration Program, said,
"This unexpected new discovery is a reminder that Spirit and
Opportunity are still doing cutting-edge exploration more than three
years into their extended missions. It also reinforces the fact that
significant amounts of water were present in Mars' past, which
continues to spur the hope that we can show that Mars was once
habitable and possibly supported life."
The newly discovered patch of soil has been given the informal name
"Gertrude Weise, " after a player in the All-American Girls
Professional Baseball League, according to Ray Arvidson of Washington
University in St. Louis, deputy principal investigator for the
rovers.
"We've looked at dozens of disturbed soil targets in the rover tracks,
and this is the first one that shows a high silica signature, " said
Ruff, who last month proposed using Spirit's miniature thermal
emission spectrometer to observe this soil. That instrument provides
mineral composition information about targets viewed from a distance.
The indications it found for silica in the overturned soil prompted a
decision this month to drive Spirit close enough to touch the soil
with the alpha particle X-ray spectrometer. Silica commonly occurs on
Earth as the crystalline mineral quartz and is the main ingredient in
window glass. The Martian silica at the Gertrude Weise patch is
non-crystalline, with no detectable quartz.
Spirit worked within about 50 yards of the Gertrude Weise area for
more than 18 months before the discovery was made. "This discovery
has driven home to me the value of in-depth, careful exploration, "
Squyres said. "This is a target-rich environment, and it is a good
thing we didn't go hurrying through it."
Meanwhile, on the other side of the planet, Opportunity has been
exploring Victoria Crater for about eight months. "Opportunity has
completed the initial survey of the crater's rim and is now headed
back to the area called Duck Bay, which may provide a safe path down
into the crater, " said John Callas, project manager for the rovers at
the Jet Propulsion Laboratory.
For images and information about the rovers, visit: http://www.nasa.gov/rovers
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