Sojourner became the first wheeled vehicle to operate on Mars in 1997.
NASA’s Mars Pathfinder mission delivered Sojourner to the Martian surface on 4 July 1997. The rover was named after Sojourner Truth, the 19th-century American abolitionist and women’s-rights advocate. It traveled around the lander, examining rocks and soil while Pathfinder relayed data to Earth.
Sojourner weighed about 10.5 kilograms and used six wheels. It carried an Alpha Proton X-ray Spectrometer for measuring the elemental composition of rocks and soil. Its small size allowed engineers to test autonomous hazard avoidance and rover operations before later, much larger missions.
Sojourner is sometimes confused with Spirit and Opportunity, which arrived in 2004, or Curiosity, which landed in 2012. It was not the first robotic vehicle on another world—that distinction belongs to Lunokhod 1 on the Moon—but it was the first rover on Mars.