The strongest evidence yet that ancient Mars was much wetter
than it is now has been unearthed by NASA's Spirit rover.
A patch of Martian soil
kicked up and analyzed by Spirit appears to be rich in silica, which suggests
it would have required
water to produce.
Chemical analysis performed by the rover's robotic
arm-mounted science instruments measured a composition of about 90 percent pure
silica -- a material commonly found in quartz on Earth -- for the bit of
Martian dirt, said mission scientists, who first heard of the find during a
teleconference.
"You could hear people gasp in astonishment," said
Steve Squyres, principal investigator for NASA's twin Spirit and Opportunity
rovers at Cornell University in Ithaca, New York. "This is a remarkable
discovery."
Draggin' the line
This discovery came about unexpectedly as the result of a
mechanical failure.
Both Spirit and its twin rover Opportunity completed their original
three-month missions in April 2004, and are aging. One of Spirit's six
wheels no longer rotates, gouging a deep impression as it drags through soil.
That scraping has exposed several patches of bright soil, leading to some of
Spirit's biggest discoveries in its Gusev
Crater exploration site, including the most recent find.
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.
One possible origin for the silica may have been interaction
of soil with acid vapors produced by volcanic activity in the presence of water,
though the material could also have formed in water in a hot spring environment,
NASA said in a statement. The latest discovery adds compelling new evidence for
ancient conditions that might have been favorable for life, the space agency
added.
Researchers informally dubbed the newly exposed patch of
soil "Gertrude Weise," after a player in the All-American Girls
Professional Baseball League.
"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 Steve Ruff, of Arizona State University in Tempe, who first
proposed using Spirit's thermal emission spectrometer to study the overturned
soil's mineral composition last month.
Heart of glass
The silica readings in the overturned soil prompted mission
managers to drive Spirit close enough to touch the soil with the rover's alpha
particle X-ray spectrometer. Silica commonly occurs on Earth as the mineral
quartz, and is the main component of window glass, NASA said. The Martian
silica at the Gertrude Weise patch is non-crystalline, with no detectable
quartz, the agency added.
Spirit
worked within about 50 yards of the Gertrude Weise area for more than 18 months
before the discovery was made.
"This
is a target-rich environment, and it is a good thing we didn't go hurrying
through it," said Squyres.
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