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	The rock "Cake," a potential target for Spirit.

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 Mössbauer 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.

Mössbauer 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.

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 .

NEWS RELEASE: 2004-046