It is spring at Gusev Crater on Mars, which would be good news for NASA’s Spirit Rover–except that Spirit, moving around after a long, hard winter, seems sporadically to have lost its mind. Last Sunday, NASA says, the rover sent a signal confirming it had received its driving instructions for the day from earth, but when it next reported in, it had not moved. That can happen for many reasons — it often has, in fact — but there was more going on. The rover had no recollection, if you will, of what it had been doing; it hadn’t recorded its main functions in its computer memory. Controllers at the Jet Propulsion Lab in California ordered the rover to find the sun with its cameras, figuring it might have stayed in place because it wasn’t sure of its position. On Wednesday the rover reported back that it had successfully found the sun, but not in the proper location. So today they’re going through more data, sending and receiving more signals — a painfully slow process, since they only get to communicate with Spirit or its twin, Opportunity, a couple of times a day, when they can relay signals through orbiting probes. "It’s in control of the ground, it’s healthy, there are just these strange things going on that they’re trying to understand," said JPL’s Guy Webster this afternoon. He promised an update, but said it will take time. So what happened? A stray blast of cosmic radiation? An aging piece of equipment having a short? A transient glitch? The computer memory seems fine now. But Spirit’s solar panels are so encrusted in red dust that they collect a fraction of the power they used to, and one wheel stopped turning years ago. Keep in mind the flip side: Spirit ran into this bit of trouble on its 1,800th day on the Martian surface. NASA, perhaps trying to keep expectations low, had originally said it expected each rover to last for 90. The rovers have sent back beautiful images, some of which we’ve assembled HERE. But it’s lasted four years in a cold, hostile place, very far from home. ========== UPDATE from NASA late Thursday: "Diagnostic activities performed by Spirit on Thursday, Jan. 29 narrowed the range of factors that may have contributed to its unexpected behavior earlier in the week. No clear explanation has been established yet. Spirit is healthy and responding to commands. It recorded and returned images of nearby scientific targets. The rover team plans further diagnostics on Friday of Spirit’s inertial measurement unit — a combined gyroscope-and-accelerometer device that measures rover movements and attitude. Spirit may resume driving over the weekend."