The Mars Rover Spirit started acting erratically early this week, according to NASA late on Wednesday afternoon. Spirit and its Mars rover companion, Opportunity, have been working on the despite initially being given an on-planet lifespan of three months.

"We don't have a good explanation yet for the way Spirit has been acting for the past few days," said Sharon Laubach, a team chief at NASA's . "Our next steps will be diagnostic activities."

NASA said that on Sunday, Spirit sent information back to Earth indicating that it had received its driving commands for the day, but did not move. And on the same day, the rover failed to record its activities, as it normally does, into its own memory.

Then on Monday, the rover's controllers sent the robotic machine instructions to find the sun with its camera, in the hopes that that would enable Spirit to re-orient itself. The rover reported back that it was unable to find the sun.

Engineers and scientists at NASA say that cosmic rays hitting the electronics onboard the rover could be causing the trouble.