January 20, 2004
Tests on
Martian Soil Reveal Surprising Results
The first use of the tools on the arm of
NASA's Mars Exploration Rover Spirit reveals puzzles about the
soil it examined and raises anticipation about what the tool
will find during its studies of a martian rock.
Today and overnight tonight, Spirit is
using its microscope and two up-close spectrometers on a football-sized
rock called Adirondack, said Jennifer Trosper, mission manager
at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
The Patch of Tested Soil
Click
for larger image
Courtesy NASA/JPL/Cornell
Scientists today reported initial impressions
from using Spirit's alpha particle X-ray spectrometer, Moessbauer
spectrometer and microscopic imager on a patch of soil that was
directly in front of the rover after Spirit drove off its lander
Jan. 15.
"We're starting to put together a
picture of what the soil at this particular place in Gusev Crater
is like. There are some puzzles and there are surprises,"
said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal
investigator for the suite of instruments on Spirit and on Spirit's
twin, Opportunity.
One unexpected finding was the Moessbauer
spectrometer's detection of a mineral called olivine, which does
not survive weathering well. This spectrometer identifies different
types of iron-containing minerals; scientists believe many of
the minerals on Mars contain iron. "This soil contains a
mixture of minerals, and each mineral has its own distinctive
Moessbauer pattern, like a fingerprint," said Dr. Goestar
Klingelhoefer of Johannes Gutenberg University, Mainz, Germany,
lead scientist for this instrument.
The lack of weathering suggested by the
presence of olivine might be evidence that the soil particles
are finely ground volcanic material, Squyres said. Another possible
explanation is that the soil layer where the measurements were
taken is extremely thin, and the olivine is actually in a rock
under the soil.
Scientists were also surprised by how little
the soil was disturbed when Spirit's robotic arm pressed the
Moessbauer spectrometer's contact plate directly onto the patch
being examined. Microscopic images from before and after that
pressing showed almost no change. "I thought it would scrunch
down the soil particles," Squyres said. "Nothing collapsed.
What is holding these grains together?"
Information from another instrument on
the arm, an alpha particle X-ray spectrometer, may point to an
answer. This instrument "measures X-ray radiation emitted
by Mars samples, and from this data we can derive the elemental
composition of martian soils and rocks," said Dr. Johannes
Brueckner, rover science team member from the Max Planck Institute
for Chemistry, Mainz, Germany. The instrument found the most
prevalent elements in the soil patch were silicon and iron. It
also found significant levels of chlorine and sulfur, characteristic
of soils at previous martian landing sites but unlike soil composition
on Earth.
Squyres said, "There may be sulfates
and chlorides binding the little particles together." Those
types of salts could be left behind by evaporating water, or
could come from volcanic eruptions, he said. The soil may not
have even originated anywhere near Spirit's landing site, because
Mars has dust storms that redistribute fine particles around
the planet. The next target for use of the rover's full set of
instruments is a rock, which is more likely to have originated
nearby.
Spirit landed in the Connecticut-sized
Gusev Crater on Jan. 3 (EST and PST; Jan. 4 Universal Time).
In coming weeks and months, according to plans, it will examine
rocks and soil for clues about whether the past environment there
was ever watery and possibly suitable to sustaining life. Spirit's
twin Mars Exploration Rover, Opportunity, will reach Mars on
Jan. 25 (EST and Universal Time; 9:05 p.m., Jan. 24, PST) to
begin a similar examination of a site on the opposite side of
the planet.
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.
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