1971 on Mars

unmanned USSR spaceprobe

Soviet Mars probe

PrOP-M (, Passability Estimating Vehicle for Mars or Device Evaluation Terrain—Mars) were two Soviet Mars rovers that were launched on the unsuccessful Mars 2 and Mars 3 missions in 1971. PrOP-M were the first rovers to be launched to Mars, 26 years before the first successful rover mission of NASA's Sojourner in 1997. Because the Mars 2 and Mars 3 missions failed, the existence of the rovers was kept secret for nearly 20 years.