All NASA Mars Exploration Rover Program Rovers

The Mars Exploration Rover (MER) program was a NASA mission that in 2004 landed twin robotic rovers, Spirit and Opportunity, on opposite sides of Mars to search for geological evidence of past water activity. Managed by the Jet Propulsion Laboratory, the two solar powered rovers were built to matching designs and launched several weeks apart in 2003, then landed three weeks apart in January 2004, Spirit in Gusev crater and Opportunity in Meridiani Planum. Both vastly outlasted their planned ninety sol primary missions, with Spirit operating for more than six years and Opportunity for over fourteen, together returning tens of thousands of images and confirming that liquid water once existed on the Martian surface. As a matched pair of rovers sharing one mission architecture, launch vehicle family, and science payload, Spirit and Opportunity are the defining members of the Mars Exploration Rover class, distinct from the larger, later Mars Science Laboratory and Mars 2020 rover programs that followed them.