Mariner 9 was the first spacecraft to photograph Mars from orbit in high resolution. NASA’s probe entered Martian orbit on November 13, 1971, becoming the first spacecraft to orbit another planet.
Mariner 9 returned more than 7,000 images during its mission. A global dust storm initially obscured much of the surface, but as the storm subsided, the spacecraft revealed volcanoes, channels, canyons, and other features that dramatically changed scientific views of Mars.
Its observations included the enormous volcanic region around Olympus Mons and the canyon system later known as Valles Marineris. The latter was named in honor of the Mariner program. Mariner 9 also photographed Mars’s two small moons, Phobos and Deimos.
Mariner 4 had already achieved the first successful close flyby of Mars in 1965, but it did not orbit the planet. That distinction is why Mariner 9 is the correct answer for the first orbital high-resolution survey.