Mariner 9

Mariner 9 was a NASA robotic space probe that became the first spacecraft ever to orbit another planet when it entered orbit around Mars in November 1971, arriving in the midst of a global dust storm that initially obscured the planet surface. Once the dust cleared, the spacecraft spent nearly a year mapping the Martian surface, returning thousands of images that revealed volcanoes, canyons and evidence of ancient riverbeds, including features later named Olympus Mons and the Valles Marineris canyon system. Its data reshaped scientific understanding of Mars and helped select landing sites for the later Viking missions.