Sojourner’s planned primary rover mission was 7 sols, or seven Martian days. NASA described this as the rover’s nominal primary mission before any extended operations were approved.
The short schedule reflected Sojourner’s experimental purpose. The small rover was designed to test mobility, autonomous navigation, hazard avoidance, wheel-soil interaction, and scientific measurements in the poorly understood Martian environment. Its primary science work included using the Alpha Proton X-ray Spectrometer to examine rocks and soil.
Sojourner reached Mars with the Pathfinder lander on July 4, 1997, and rolled onto the surface the next day. Although the plan called for only seven sols, the rover remained productive far beyond that limit. It operated for 83 sols, traveled just over 100 meters, photographed the terrain, and analyzed rocks including Barnacle Bill and Yogi.
The commonly confused numbers refer to different mission durations: 7 sols was the rover’s primary plan, while Pathfinder’s lander had a longer planned mission. Sojourner’s actual operating life was many times longer than its original schedule.