NASA’s Opportunity has examined its first patch of soil in the small
crater where the rover landed on Mars and found strikingly spherical
pebbles among the mix of particles there.

“There are features in this soil unlike anything ever seen on Mars
before,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y.,
principal investigator for the science instruments on the two Mars
Exploration Rovers.

For better understanding of the soil, mission controllers at NASA’s
Jet Propulsion Laboratory, Pasadena, Calif., plan to use Opportunity’s
wheels later this week to scoop a trench to expose deeper material.
One front wheel will rotate to dig the hole while the other five
wheels hold still.

The spherical particles appear in new pictures from Opportunity’s
microscopic imager, the last of 20 cameras to be used on the two rover
missions. Other particles in the image have jagged shapes. “The
variety of shapes and colors indicates we’re having particles brought
in from a variety of sources,” said Dr. Ken Herkenhoff of the U.S.
Geological Survey’s Astrogeology Team, Flagstaff, Ariz.

The shapes by themselves don’t reveal the particles’ origin with
certainty. “A number of straightforward geological processes can
yield round shapes,” said Dr. Hap McSween, a rover science team member
from the University of Tennessee, Knoxville. They include accretion
under water, but apparent pores in the particles make alternative
possibilities of meteor impacts or volcanic eruptions more likely
origins, he said.

A new mineral map of Opportunity’s surroundings, the first ever done
from the surface of another planet, shows that concentrations of
coarse-grained hematite vary in different parts of the crater. The
soil patch in the new microscopic images is in an area low in
hematite. The map shows higher hematite concentrations inside the
crater in a layer above an outcrop of bedrock and on the slope just
under the outcrop.

Hematite usually forms in association with liquid water, so it holds
special interest for the scientists trying to determine whether the
rover landing sites ever had watery environments possibly suitable for
sustaining life. The map uses data from Opportunity’s miniature
thermal emission spectrometer, which identifies rock types from a
distance.

“We’re seeing little bits and pieces of this mystery, but we haven’t
pieced all the clues together yet,” Squyres said.

Opportunity’s Moessbauer spectrometer, an instrument on the rover’s
robotic arm designed to identify the types of iron-bearing minerals in
a target, found a strong signal in the soil patch for olivine. Olivine
is a common ingredient in volcanic rocks. A few days of analysis may
be needed to discern whether any fainter signals are from hematite,
said Dr. Franz Renz, science team member from the University of Mainz,
Germany.

To get a better look at the hematite closer to the outcrop,
Opportunity will go there. It will begin by driving about 3 meters (10
feet) tomorrow, taking it about halfway to the outcrop. On Friday it
will dig a trench with one of its front wheels, said JPL’s Dr. Mark
Adler, mission manager.

Opportunity’s twin, Spirit, today is reformatting its flash memory, a
preventive measure that had been planned for earlier in the week. “We
spent the last four days in the testbed testing this,” Adler said.
“It’s not an operation we do lightly. We’ve got to be sure it works
right.” Tomorrow, Spirit will resume examining a rock called
Adirondack after a two-week interruption by computer memory problems.
Controllers plan to tell Spirit to brush dust off of a rock and
examine the cleaned surface tomorrow.

Each martian day, or “sol,” lasts about 40 minutes longer than an
Earth day. Spirit begins its 33rd sol on Mars at 2:43 a.m. Thursday,
Pacific Standard Time. Opportunity begins its 13th sol on Mars at
3:04 p.m. Thursday, PST.

Image Credit: NASA/JPL/US Geological Survey