Ground controllers plan to tell Opportunity to drive off its lander
early Saturday, and with Spirit now back in working order, NASA should
soon have two healthy rovers loose on Mars.

Early today, the controllers at NASA’s Jet Propulsion Laboratory,
Pasadena, Calif., decided to move up the time for Opportunity’s
roll-off by nearly 24 hours, to the rover’s seventh martian day since
landing last weekend. “We’re ahead of schedule and taking advantage
of the fact that Opportunity treats us well,” said JPL’s Daniel
Limonadi, rover systems engineer. “We feel it’s good to egress today
and get ready to do science earlier with six wheels on the ground in
Meridiani Planum.”

Dr. Ray Arvidson of Washington University in St. Louis, deputy
principal investigator for the rover science instruments, said, “We’re
totally ecstatic that we’re going to be on the surface.”

If a final check finds conditions OK for sending the egress commands
at about 12:30 a.m. Saturday, Pacific Standard Time, confirmation of
the roll-off would be expected between 3 a.m. and 4 a.m. PST.

Opportunity’s twin Mars Exploration Rover, Spirit, has sent back its
first new science data in more than a week. On Thursday, it took and
transmitted panoramic camera images including views of two
light-colored rocks, nicknamed Cake and Blanco. Scientists are
considering those rocks as possible targets for up-close examination
after Spirit finishes inspection of the rock called Adirondack over
the next few days.

Spirit has also returned microscopic images and Moessbauer
spectrometer readings of Adirondack taken the day before the rover
developed computer and communication problems on Jan. 22. Both are
unprecedented investigations of any rock on another planet.

The microscopic images indicate Adirondack is a hard, crystalline
rock. “If you had a hammer and whacked that rock, it would ring,”
Arvidson said.

Moessbauer readings allow scientists to determine what types of
iron-bearing minerals are in a rock. “What made us extremely happy
when we saw the graph for the first time were the small peaks,” said
Dr. Bodo Bernhardt, a member of the rover science team from the
University of Mainz, Germany, which provided the instrument. The peaks
large and small in the spectrum reveal that the minerals in Adirondack
include olivine, pyroxene and magnetite. That composition is common in
volcanic basalt rocks on Earth, said science-team member Dr. Dick
Morris of NASA’s Johnson Space Center, Houston.

In coming days, scientists plan to use Spirit’s rock abrasion tool to
grind the weathered surface off of a small area on Adirondack to
inspect its interior. Later plans include examining a nearby whitish
rock, then driving toward a crater nicknamed Bonneville that’s about
250 meters (820 feet) away. Researchers will use the rover to search
for rocks that may have been excavated from below the surface and
tossed outward by the impact that dug the crater. If Spirit can reach
the rim, scientists hope to see outcrops in the crater walls.

Engineers are continuing to restore Spirit to full health as the rover
makes scientific observations, said JPL’s Dr. Mark Adler, mission
manager. They plan to delete from the rover’s flash memory a large
amount of information stored before landing, then resume operating
Spirit in a normal mode that uses flash memory.

Halfway around the planet, Opportunity’s main task in the days after
roll-off will be to take microscopic images and spectrometer readings
of the soil close to the lander. Within about a week, controllers
anticipate sending the rover to an outcrop of bedrock about 8 meters
(26 feet) northwest of the lander.

Opportunity currently sits near the center of a crater 22 meters (72
feet) across and 3 meters (10 feet) deep. A new three-dimensional
model of the crater, created from information in stereo images, will
provide a reference for rover driving within the crater and later for
choosing a route out onto the surrounding plains, said Dr. Ron Li, a
rover science team member from Ohio State University, Columbus. This
is the first time a crater on another planet has been mapped from
inside the crater.