<P> NASA's Mars Exploration Rover (MER) mission is an ongoing robotic space mission involving two Mars rovers, Spirit and Opportunity, exploring the planet Mars . It began in 2003 with the launch of the two rovers: MER - A Spirit and MER - B Opportunity--to explore the Martian surface and geology; both landed on Mars at separate locations in January 2004 . Both rovers far outlived their planned missions of 90 Martian solar days: MER - A Spirit was active until 2010, while MER - B Opportunity is still active in 2018, and holds the record for the longest distance driven by any off - Earth wheeled vehicle . </P> <P> The mission's scientific objective was 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 program landers in 1976 and Mars Pathfinder probe in 1997 . </P>

What are the names of the two rovers currently exploring mars