The Sojourner rover (officially named Sojourner Truth after the American abolitionist) is an exploratory robot which landed on Mars on July 4, 1997.  Sojourner was part of NASA's Mars Pathfinder mission, dedicated to exploring the surface of Mars. As planned, Sojourner rolled around the planet's surface taking scientific readings of various bits of rock and soil. The plucky robot lasted until at least September, when its communications with Earth were finally cut off due to failing power.