[meteorite-list] Spirit Adds Clues About History of Rocks in Martian Hills

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Nov 4 15:57:01 2004
Message-ID: <200411042056.MAA17107_at_zagami.jpl.nasa.gov>


Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Donald Savage (202) 358-1547
NASA Headquarters, Washington, D.C.

News Release: 2004-269 November 4, 2004

Spirit Adds Clues About History of Rocks in Martian Hills

All the scientific tools on NASA's two Mars Exploration
Rovers are still working well, a full 10 months after
Spirit's dramatic landing.

The ones on Spirit are adding fresh evidence about the
history of layered bedrock in a hill the rover is climbing.

"Our leading hypothesis is that these rocks originated as
volcanic ash that fell from the air or moved in ground-
hugging ash flows, and that minerals in them were altered by
water," said Dr. Ray Arvidson of Washington University, St.
Louis, deputy principal investigator for the mission.

"This is still a working hypothesis, not a firm conclusion,
but all the instruments have contributed clues that fit," he
said. "However, it is important to point out that we have
just begun to characterize the textures, mineralogy and
chemistry of these layered rocks. Other hypotheses for their
origin focus on the role of transport and deposition by
water. In fact, it may turn out that volcanism, water and
wind have produced the rocks that Spirit is examining. We are
just beginning to put together the big picture."

Both rovers completed three-month primary missions in April.
NASA has extended their missions twice because they have
remained productive longer than anticipated.

"We're still making good progress even though Spirit has two
types of problems with its wheels," said Jim Erickson, rover
project manager at NASA's Jet Propulsion Laboratory,
Pasadena, Calif. "We are working around those problems
successfully, but they might be a sign of things to come, as
mechanical parts wear out during our exploration of Mars."

One question for continuing investigations as Spirit heads
for rocks higher in the "Columbia Hills," is what the
environment was like when water altered the minerals.
Possibilities include water in the volcanic magma mixture
before the ash erupted, surface water transporting the ash
while it was still loose after the eruption, and ground water
soaking through the rocks that solidified from the
accumulated ash.

Some clues for a volcanic-ash origin come from a layered rock
dubbed "Uchben." Researchers pointed Spirit's microscopic
imager at a spot on Uchben scoured with the rock abrasion
tool. The images reveal sand-size particles, many of them
sharply angular in shape and some quite rounded. The
angularity is consistent with transport by an eruption.
Particles carried across the surface by wind or water usually
tumble together and become more rounded. Uchben's rounded
particles may be volcanic clumps, may be concretions similar
to what Opportunity has found, or may be particles tumbled in
a water environment.

Evidence for alteration by water comes mainly from
identification of minerals and elements in the rocks by the
rover's Moessbauer spectrometer and alpha particle X-ray

The rovers' principal investigator, Dr. Steve Squyres of
Cornell University, Ithaca, N.Y., said, "We have really made
headway just in the last several weeks in understanding these
rocks. The most likely origin is debris that blasted out of a
volcano, was transported by air or water to its present
location, and settled out in layers."

Opportunity, meanwhile, examined a lumpy boulder called
"Wopmay" inside "Endurance Crater." The slope of the ground
and loose surface material around the rock prevented
Opportunity from getting firm enough footing to use its rock
abrasion tool. Evidence from the spectrometers and
microscopic imager is consistent with scientists' earlier
hypothesis that rocks near the bottom of the crater were
affected by water both before and after the crater formed.
The evidence is still not conclusive, Squyres said.

Opportunity is heading toward the base of "Burns Cliff," a
tall exposure of layered rock in the wall of the crater.
However, if the rover encounters more of the poor traction
found around Wopmay, planners may change course and drive up
out of the crater.

JPL, a division of the California Institute of Technology in
Pasadena, manages the Mars Exploration Rover project for
NASA's Science Mission Directorate, Washington. Images and
additional information about the project are available from
JPL at http://marsrovers.jpl.nasa.gov and from Cornell
University at http://athena.cornell.edu .

Received on Thu 04 Nov 2004 03:56:59 PM PST

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