Instead of one kilometer, Opportunity has driven 38.7 kilometers, or about 24 miles, exploring a series of ever larger craters, taking 170,000 pictures along the way.
Over all, the rover remains in good health, despite the lame wheel, two scientific instruments that are no longer working, and a robotic arm with arthritislike stiffness. John L. Callas, the project manager, said the rover had also suffered an “amnesia moment,” probably caused by aging memory chips.
“It’s just an operational annoyance,” Dr. Callas said. “But if it gets precipitously worse, there are some corrective actions we can take.”
Perhaps a greater obstacle to Opportunity’s continued roving might be the limits of NASA’s budget. This spring, NASA officials will review all of NASA’s spacecraft that have lived beyond their original missions. Opportunity currently costs $14 million a year.
“We have to weigh how much money we have and what missions are most productive,” said Michael Meyer, the lead scientist for NASA’s Mars exploration program.
The newly discovered rock is like nothing Opportunity has seen. Dr. Squyres said it appeared to have flipped upside down, possibly exposing its underside for the first time in several billion years. “We’re seeing stuff we don’t normally get to see,” he said.
“It looks like a jelly doughnut,” he continued: “White around the outside, red in the middle. We’ve looked at it with our microscope. It’s clearly a rock.”
The composition is strange — high in sulfur, magnesium and manganese. “This is an ongoing story of discovery,” Dr. Squyres said. “Mars keeps throwing new stuff at us.” At news conferences, NASA now solicits questions from the public via Twitter. That prompted the “Star Trek” actor William Shatner to chime in, “Are you going to cover the alien rock throwers?”
Dr. Squyres replied that he did not think there were any Martian rock throwers, but another possibility might be that the rock was knocked there by a small asteroid impact nearby.
In Friday’s issue of the journal Science, scientists report on recent analysis of rocks along the rim of the 14-mile-wide Endeavour Crater where Opportunity is currently exploring. Following readings from Mars Reconnaissance Orbiter, Opportunity headed to rocks that appeared to contain a clay mineral known as iron smectite.