Spirit Finds Multi-Layer Hints of Past Water at Mars' Gusev Site
April 1, 2004
Clues from a wind-scalloped volcanic rock on Mars investigated by NASA's
Spirit rover suggest repeated possible exposures to water inside Gusev
Crater, scientists said Thursday.
Gusev is halfway around the planet from the Meridiani region where Spirit's
twin, Opportunity, recently found evidence that water used to flow across
the surface.
"This is not water that sloshed around on the surface like what
appears to have happened at Meridiani. We're talking about small amounts
of water, perhaps underground," said Dr. Hap McSween, a rover science
team member from the University of Tennessee, Knoxville.
"The evidence is in the form of multiple coatings on the rock, as
well as fractures that are filled with alteration material and perhaps
little patches of alteration material," McSween said during a press
conference at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
The rock, called "Mazatzal" after mountains in Arizona, lies
partially buried near the rim of the crater informally named "Bonneville"
inside the much larger Gusev Crater. Its light- toned appearance grabbed
scientists' attention. After Spirit's rock abrasion tool brushed two patches
on the surface with wire bristles, a gray, darker layer could be seen
under the tan topcoat. The rock abrasion tool ground into the surface
with diamond cutting teeth on March 26. Then, after an examination of
the newly exposed material, it ground deeper into the rock two days later.
A lighter-gray interior lies under the darker layer, and a bright stripe
cuts across both.
Dr. Jeff Johnson, a science team member from the U.S. Geological Survey's
Astrogeology Team, Flagstaff, Ariz., said the stripe "seems to be
a fracture that water has flowed through, potentially with minerals precipitating
from that fluid and lining the walls of the crack."
He and other scientists stressed that the interpretations are preliminary.
"The team is, as always, trying to find time to digest these observations
while also preparing for the next day's operations," Johnson said.
Spirit's alpha particle X-ray spectrometer checked what chemical elements
were close to the surface of untreated, brushed, once-drilled and twice-drilled
patches. "Miracles, miracles, miracles. We have a lot of work to
do," the instrument's lead scientist, Dr. Rudi Rieder of the Max
Planck Institute, Mainz, Germany, exclaimed about the results. For example,
the ratio of bromine to chlorine seen inside the rock is unusually high
and possibly a clue to alteration by water.
The final experiment on Mazatzal was to scrub the surface with the rock
abrasion tool in a pattern of five circles arranged in a ring, with a
sixth circle in the center. Besides creating a rock-art daisy, this task
by the engineers of New York-based Honeybee Robotics, as well as JPL,
produced a brushed patch big enough to fill the field of view of Spirit's
miniature thermal emission spectrometer, said Dr. Steve Ruff of Arizona
State University, Tempe. The tan outer surface appears to have a strikingly
different mineral composition than the dark gray coating exposed by the
brushing, but more time is needed to complete the analysis, he said.
McSween proposed that the light outer coat, dark inner coat and bright
veins could have resulted from three different periods of the rock being
buried, altered by fluids and unburied.
While scientists await transmission of additional data Spirit has collected
about Mazatzal, the rover will be making its way toward the "Columbia
Hills" about 2.3 kilometers (1.3 miles) away. Spirit left the rock
and drove 36.5 meters (120 feet) early Thursday.
Opportunity set a one-day driving record on Mars on March 27 by covering
48.9 meters (160 feet) toward a rock called "Bounce Rock" because
airbag bounce marks show that the spacecraft hit it on landing day two
months ago. "We're looking to break that record again very soon with
longer and longer drives," said JPL's Chris Lewicki, flight director.
Before moving on across the plains of Meridiani, though, Opportunity
will complete an investigation it has begun of Bounce Rock. The rock is
unlike any seen on Mars before, said Dr. Jim Bell, lead scientist for
the rovers' panoramic cameras. "There are some shiny surfaces on
this rock," he said, describing them as "almost mirrorlike."
The two rovers' 18 cameras have now taken more than 20,000 images. JPL,
a division of the California Institute of Technology in Pasadena, manages
the Mars Exploration Rover project for NASA's Office of Space Science,
Washington, D.C.
Images and additional information about the project are available from
JPL at http://marsrovers.jpl.nasa.gov
and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu
.
