Mariner 9 was the first spacecraft to orbit Mars successfully. NASA placed it into Martian orbit on November 13, 1971, making it the first artificial satellite of another planet.
The spacecraft arrived during a global dust storm, which initially obscured much of Mars’s surface. As the dust settled, Mariner 9 photographed volcanoes, canyons, polar regions and other features in unprecedented detail.
Its observations helped reveal Olympus Mons and Valles Marineris, although those names and interpretations developed through the mission’s imaging work and later analysis. Mariner 9 operated until October 1972.
Mars 2 reached Mars around the same time but did not become a successful orbiter. Viking 1 arrived later, in 1976, and is better known for its lander and long-lived orbiter.