<P> In January 2004 , the NASA twin Mars Exploration Rovers named Spirit ( MER - A ) and Opportunity ( MER - B ) landed on the surface of Mars . Both have met or exceeded all their targets . Among the most significant scientific returns has been conclusive evidence that liquid water existed at some time in the past at both landing sites . Martian dust devils and windstorms have occasionally cleaned both rovers ' solar panels , and thus increased their lifespan . Spirit Rover ( MER - A ) was active until 2010 , when it stopped sending data because it had fallen into a sand dune . </P>
when did we first put a rover on mars
January 2004