Mariner 9 was the first spacecraft to orbit Mars successfully for an extended mission.
NASA’s Mariner 9 entered Martian orbit on November 13, 1971. It became the first spacecraft to orbit another planet, although the Soviet Mars 2 probe reached Mars shortly afterward and also entered orbit. Mariner 9 returned more than 7,000 images.
Its arrival coincided with a planet-wide dust storm, initially hiding most of the surface. When the storm settled, the spacecraft revealed enormous volcanoes, including Olympus Mons, and the vast Valles Marineris canyon system.
Mariner 9 is often mixed up with Mariner 4, which made the first successful close flyby of Mars in 1965. A flyby passes the planet, while an orbiter fires its engines to remain gravitationally bound.