After five months on the frigid surface of Mars, one of NASA's hardy rovers is finally beginning to succumb to old age, developing a robotic form of arthritis that could limit its ability to climb steep slopes, officials said today.

Spirit's latest panorama shows the view from the bottom of the hills. Credit: NASA/JPL Download a larger version here

"We've joked in the past about being past warranty on these rovers," said mission manager Mark Adler. "Now we're actually seeing some signs of being past warranty, we're beginning to see some real degradation.

"They were designed for a three-month lifetime, they're already now two months past that. These rovers could continue to operate for several more months. Or they could stop and fail tomorrow. We don't know. But we're going to continue to operate the rovers, continue to do ... what we can to keep the rovers operating for as long as possible."

On one side of Mars, the Opportunity rover remains in good health as it descends into Endurance crater in search of more clues about Mars' watery past. While engineers have been putting Opportunity into "deep sleep" at night to conserve power, the low overnight temperatures have not yet affected its most sensitive instrument, a critical spectrometer.

As Opportunity carefully creeps down the crater's steep slope, it is effectively taking geologists back in time in their search for rocks that formed earlier than those at the surface or even in Eagle crater, where Opportunity landed in late January.

Rocks like those seen at Eagle are visible inside Endurance crater and below them, different sorts of deposits that have scientists especially excited.

Opportunity's drive into Endurance Crater is illustrated day-by-day. Credit: NASA/JPL Download a larger version here

"Opportunity is about to open what we hope is the second chapter of the book on Meridiani," Adler said, referring to the plain of Meridiani where Opportunity landed. "It's currently investigating a rock that we believe is from the first chapter to get our bearings straight as we proceed on a couple-of-meter trip back in time."

Engineers spent weeks photographing Endurance crater from various angles to determine the steepness of the slopes leading into the depression to make sure Opportunity could safely enter and exit.

"The crater has actually been behaving exactly as we expected, the rover has been behaving as we expected on the slopes of the crater, we've seen exactly the slippage that we expected," Adler said. "We've gone into the crater, gone back out and back in again to make sure that we can do that.

"Right now, we have no reason to believe we're not able to traverse the crater, we have no reason to believe we won't be able to get out of the crater."

In fact, he added, the science team "is already looking past the current objective in Opportunity's crater and they're starting to see some things down farther they may want to go look at."

A stunning new panorama from Opportunity shows Endurance Crater and the vast plains. Credit: NASA/JPL Download a larger version here

On the other side of Mars, in the heart of Gusev crater, the Spirit rover is now poised at the base of the Columbia hills, a formation named after the fallen shuttle astronauts. The Columbia hills are 2.1 miles from Spirit's landing site and scientists are excited about the prospect of studying rock outcrops at higher elevations in search of clues about what happened to the water that once flowed into the crater.

But the six-wheeled Spirit is beginning to show signs of wear and tear that may impose limitations on future exploration.

"Spirit is beginning to show some signs of age," Adler said. "We are now seeing, after our three-kilometer trek across the desert, that the right front wheel motor is now taking two or three times the current the other wheels are taking to do the same job.

"That current draw has been increasing steadily, and so we're seeing a real degradation in the motor. There appears to be some sort of resistance in the gear box the motor uses to (reduce) the motor revolutions to the actual wheel revolutions."

Engineers at the Jet Propulsion Laboratory in Pasadena, Calif., are working to more fully diagnose the problem. In the near term, they plan to heat up the gearbox in hopes of redistributing lubrication that may have been affected by low temperatures.

"But that may or it may not help," Adler said. "If it doesn't help, we're looking at options to either run the wheel to its end of life or to turn the wheel off and drive the rover on five wheels and preserve that wheel for occasional use when we need the extra torque to climb up a hill or we need the accuracy to approach a rock. The rover can work pretty well on five wheels."

Spirit's trek from its landing site to the hills is mapped out. Credit: NASA/JPL Download a larger version here

Spirit also is suffering a slight temperature-related hearing problem. Last week, a day's worth of data was lost when flight controllers were unable to synch up with Spirit's radio receiver to uplink commands. But engineers should be able to work around that problem.

"So right now, what we're seeing is that Spirit has gotten a little hard of hearing due to temperature, not due to age," Adler said. "And also, she's experienced a little bit of arthritis in one of her joints, and that is due to age, that's a real degradation."

Engineers believe the motor has only "a couple of hundred meters" of life left in it. But Adler said they are optimistic about developing a strategy that will allow Spirit to continue its exploration for many more weeks, if not months.

A bigger question mark looming for rover engineers is how to keep the rovers alive through August and September, when the robots will have to stand down for the harsh martian winter.

Additional coverage for subscribers:
VIDEO: RIDE WITH OPPORTUNITY AS IT DRIVES INTO CRATER QT
VIDEO: OPPORTUNITY'S NEW COLOR PANORAMA WITH NARRATION QT
VIDEO: SPIRIT'S PANORAMA FROM BASE OF THE HILLS QT
VIDEO: LATEST SPIRIT PICTURES WITH NARRATION QT
VIDEO: WATCH TODAY'S MARS ROVER NEWS CONFERENCE QT
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