Mariner 9 became the first spacecraft to orbit another planet when it entered orbit around Mars in 1971.
NASA launched Mariner 9 on 30 May 1971, and the spacecraft reached Mars on 13 November 1971. It entered an elliptical orbit, allowing it to observe the planet repeatedly rather than making only a single flyby.
A global dust storm initially obscured much of Mars’s surface, but the spacecraft continued operating until the atmosphere cleared. Mariner 9 then mapped volcanoes, canyons, channels and the polar regions, greatly expanding knowledge of Martian geology.
Mariner 4 had previously performed the first successful Mars flyby in 1965, but it never entered orbit. Viking 1 and Viking 2 arrived later and included landers, while Mariner 9 was an orbiter only.