Sojourner rover

Rover. Although Russian Mars 2 and Mars 3 descent modules brought rovers with them as early as 1971, no rover was successfully deployed on Mars until the U.S. Pathfinder mission of 1997 deployed its Sojourner rover. Able to travel about a half kilometer, or one-third of a mile from the lander, the Sojourner rover returned 550 photographs to Earth and the data from chemical analyses of sixteen locations on the Martian surface. 

The first objective for the Sojourner was to show that it could function in the little-known environment on the surface of Mars and to observe its behavior in order to make design improvements in future rovers. Sojourner moved around the immediate area of the lander, butting the APXS up against rocks. Detectors measured interactions between a radioactive source in the APXS and the surface materials by obtaining an energy spectrum of the alpha particles, protons, and x rays produced by the exposure. This instrument could determine the chemical composition of materials, including the amounts present of most major elements except hydrogen. 

On July 4, 1997, after a 7-month trip, the Pathfinder spacecraft landed on Mars and released a small robot rover called Sojourner. The weight of an objea on Mars is about 38% of the weight of the same object on Earth. 

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