When NASA's Spirit and Opportunity rovers touched down on Mars, they were each tapped for three-month missions exploring the Red Planet. But five years later, both are still moving, providing a bright spot at a tumultuous time for the space agency.

Last Saturday marked the five-year anniversary of Spirit's landing on Mars, the start of an astonishingly long run by the rovers. (Opportunity landed safely three weeks later.) "The American taxpayer was told three months for each rover was the prime mission plan," Ed Weiler, associate administrator for NASA's Science Mission Directorate, said in a statement. "The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times."

During their lengthy lifetimes, the rovers have made countless geological measurements and beamed back thousands of photographs of the Martian surface. But their work isn't done yet. NASA has plans for Spirit to investigate nearby surface features that might yield clues to Mars's volcanic activity. And Opportunity is being sent on a much longer fact-finding mission to explore Endeavour Crater, a massive depression so distant from the rover's previous position (12 kilometers, or about seven miles) that the trip roughly matches Opportunity's total mileage over its first five years.

Artist's conception of one of the rovers on Mars courtesy of JPL/NASA