Late last week, appeared to twice reboot its computer, unprompted from the ground. Then NASA engineers learned that the robotic rover had failed to even wake up to send its regularly scheduled downlink of information, according to John Callas, NASA's project manager for Spirit and its Mars rover companion, Opportunity. Then it didn't wake up for two other communication sessions.

Scientists knew they had a problem. But the engineering team is still looking for the specific problem, said Callas in an interview with Computerworld.

"If it just needs to be reset, we can do that," said Callas. "If something is permanently broken, that's a bigger issue. It's still very early in the analysis."

Both a computer glitch back in January, and Opportunity, which has remained relatively healthy, have been working on the Martian surface for five years, far more than the three-month life span initially projected by NASA.

The two rovers are some of the best pieces of technology that the ever built, said Bruce Banerdt, project scientist for the Mars Exploration Rovers, in a previous interview.