The mission was only supposed to last three months, maybe six months if all went well, but the Mars Exploration Rovers surprised everyone. Demonstrating an uncanny kind of "robot right stuff," they roved far beyond what anyone dreamed and now, in a matter of days, Spirit and Opportunity will celebrate their 4th birthdays and rove into their fifth year of exploring the Red Planet.
Dust from the sky has settled on both the rover deck and the surrounding landscape. The dust-covered solar cells will not be able to generate as much power as when they were clean. Unless a puff of wind dusts off the solar panels, Spirit may have difficulty surviving the approaching Martian winter.