Opportunity, also known as MER-B (Mars Exploration Rover – B) or MER-1, is a robotic rover active on Mars since 2004. Launched on July 7, 2003 as part of NASA's Mars Exploration Rover program, it landed in Meridiani Planum on January 25, 2004, three weeks after its twin Spirit (MER-A) touched down on the other side of the planet. With a planned 90 sol duration of activity, Spirit functioned until getting stuck in 2009 and ceased communications in 2010, while Opportunity remains active as of 2016, having already exceeded its operating plan by (in Earth time). Opportunity has continued to move, gather scientific observations, and report back to Earth for over 48 times its designed lifespan.