Spirit and Opportunity the Twin Mars Rovers

NASA's Mars Exploration Rover Mission was a robotic space mission which began in 2003 and sent two rovers, Spirit and Opportunity, to explore Mars.
MER-A (Spirit) and (MER-B) Opportunity explored the Martian surface and sent back pictures and data about the planet's geology .

The mission's scientific objective was to search for and characterise a wide range of rocks and soil samples in the hope of finding clues to past water activity on Mars. NASA's Mars Exploration Programme also includes three previous successful landers: the two Viking program landers in 1976 and Mars Pathfinder probe in 1997.