Mariner 9 (Mariner I)

In 1971, the Mariner 9 spacecraft beat the Soviet Mars 2 to the Red Planet to become the first spacecraft to orbit another planet. While in orbit, Mariner 9 mapped 85 percent of the Martian surface, an objective it inherited from the failed Mariner 8 mission, and collected valuable information about Mars' surface and atmosphere.

Of the more than 7,000 images it transmitted, some of the most significant were the first detailed views of the solar system's largest volcano, a canyon system that dwarfs the Grand Canyon and the Martian moons Phobos and Deimos.