Mars Exploration Rovers

NASA's Mars Exploration Rover (MER) Mission is an ongoing robotic mission of exploring Mars, that began in 2003 with the sending of two rovers - Spirit and Opportunity - to explore the Martian surface and geology. The mission is led by Project Manager Peter Theisinger of NASA's Jet Propulsion Laboratory and principal investigator Steven Squyres, professor of astronomy at Cornell University.
Primary among the mission's scientific goals is to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The mission is part of NASA's Mars Exploration Program which includes three previous successful landers: the two Viking landers in 1976 and Pathfinder in 1997.
The total cost of building, launching, landing and operating the rovers on the surface for the initial 90 day primary mission was about US $820 million. Since the rovers are still functioning over three years after landing, mission funding has been extended to "possibly through 2009". In July of 2007, Martian dust storms blocked sunlight to the rovers and threatened the ability of the craft to gather energy through their solar panels, causing engineers to fear that one or both of them might be permanently disabled; however, as of August 24, 2007, the dust storms have lifted and both rovers have resumed operations.

In recognition of the vast amount of scientific information amassed by both rovers, two asteroids have been named in their honor: 37452 Spirit and 39382 Opportunity.