Also, a newly completed 360-degree color panorama from Opportunity shows a trail of bounce marks coming down the inner slope of the small crater where the spacecraft came to rest when it landed on Mars nine days ago.

Opportunity extended its arm early today for the first time since pre-launch testing. "This was a great confirmation for the team," said Joe Melko of NASA's Jet Propulsion Laboratory, Pasadena, Calif. Melko is mechanical systems engineer for the arm, which is also called the instrument deployment device.

Mission controllers at JPL are telling Opportunity to use two of the instruments on the arm overnight tonight to examine a patch of soil in front of the rover. A microscope on the arm will reveal structures as thin as a human hair and a Moessbauer Spectrometer will collect information to identify minerals in the soil, according to plans. Tomorrow, the rover will be told to turn the turret at the end of the arm in order to examine the same patch of soil with another instrument, the alpha particle X-ray spectrometer, which reveals the chemical elements in a target.

Spirit is now in good working order after more than a week of computer-memory problems. It is brushing dust off of a rock today with the rock abrasion tool on its robotic arm. After the brushing, Spirit will use the microscope and two spectrometers on the arm to examine the rock.

"We're moving forward with our science on the rock Adirondack," said JPL's Jennifer Trosper, Spirit mission manager. Reformatting of Spirit's flash memory was postponed from today to tomorrow. The reformatting is a precautionary measure against recurrence of the problem that prevented Spirit from doing much science last week.

Later in the week, Spirit will grind the surface off of a sample area on Adirondack with the rock abrasion tool to inspect the rock's interior. After observations of Adirondack are completed, the rover will begin rolling again. "We are already strategizing how to drive far and fast," Trosper said.

Observations by each rover's panoramic camera help scientists choose where to drive and what to examine with the instruments on each rover's arm. Dr. Jeff Johnson, a rover science team member from the U.S. Geological Survey's Astrogeology Team, Flagstaff, Ariz., said that 14 filters available on each rover's panoramic camera allow the instrument to provide much more information for identifying different types of rocks than can be gleaned from color images such as the new panoramic view.

"By looking at the brightness values in each of these wavelengths, we can start to get an idea of the things we're interested in, especially to unravel the geological history of these landing sites," Johnson said.

The main task for both rovers in coming weeks and months is to find clues in rocks and soil about past environmental conditions, particularly about whether the landing areas were ever watery and possibly suitable for sustaining life.

Each martian day, or "sol" lasts about 40 minutes longer than an Earth day. Spirit begins its 31st sol on Mars at 1:23 a.m. Tuesday, Pacific Standard Time. Opportunity begins its 11th sol on Mars at 1:44 p.m. Tuesday, PST. The two rovers are halfway around Mars from each other. 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.