Opportunity used its Microscopic Imager (MI), a cross between a microscope and digital camera at the end of its robot arm, to look at a small portion of a pebble field first seen by a different camera. Looking at an area about three centimeters wide, the imager found a wide variety of larger pebbles sitting on a bed of fine sand.
The closer inspection, however, found those pebbles not so round -- and some full of holes -- but they may still yield clues into their formation, mission scientists said during the press briefing at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. The rocks may be the remains of a meteorite impact or the solidified remnant of molten lava ejected by a Martian volcano.
"We're having particles here from a variety of sources," explained Ken Herkenhoff, a USGS geologist and MI element lead for MER. "These holed rocks formed probably by volcanic processes."
In addition to taking microscopic images of the pebbles -- the largest one seen is about three millimeters wide -- Opportunity's handlers used the a Mssbauer spectrometer on the rover arm to search for signs of hematite, a mineral formed when iron is exposed to oxygen and water, among the pebbles. There was only a small amount, but not surprising since a mineral map generated by Opportunity's Miniature Thermal Emission Spectrometer (Mini-TES) showed the robot as sititng in a hematite-poor region of its landing site, Meridiani Planum.
"This is the first mineral map ever done on the surface of another planet," Squyres said. Opportunity's robotic twin Spirit used its Mini-TES to create a temperature map, not mineral, of its Gusev Crater landing site, he added.
In the Opportunity map, the circular bounce marks from the rover's airbag landing apparently disturbed the layout of hematite at Meridiani Planum.
Squyres said that starting Thursday, Opportunity should begin heading into a hematite-rich region on its way to a rock outcropping about 20 feet (six meters) away. Ten feet into that journey, the rover is scheduled to dig a trench in the Martian soil with a front wheel and study its contents using the instruments on its arm.
In addition Opportunity, JPL scientists have been hard at work on Spirit in efforts to return the rover to its science mission following a software malfunction traced to its rewriteable flash memory system. They had hoped the probe would be able to complete its studies on the nearby rock Andirondack, but Spirit failed to find Sun Monday - possibly due to a corrupt computer file in its flash memory -- and science operations were once again stalled.
Spirit Mission manager Mark Adler said that today Spirit's handlers have begun reformatting the robot's flash memory, which is suspected to be the source of its recent computer malfunction. The process includes a four-hour memory wipe to erase all of Spirit's flash memory followed by a system reboot. In the meantime, project scientists are also continuing a hardware check to be sure it is working properly.
"This is not an operation that we do lightly," Adler said, adding that the flash erase process should abort if it causes any abnormal side effects in other rover operations. "In fact, we do checks every step of the way."
The Spirit rover should resume normal science operations by Feb. 5, Adler added.
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