From the NASA Jet Propulsion Laboratory:
Two Mars Exploration Rovers, Spirit and Opportunity, landed on the Red Planet in January, 2004, on a 90-day mission. Spirit's mission lasted 2,269 days (over 6 years) and ended in 2010. Ten years after landing, the Opportunity rover continues to explore. The rover's science team explains how Opportunity traversed the Red Planet, examined the diverse environment and sent back data that transformed our understanding of Mars.