The unmanned NASA/JPL space probe Mariner 9 enters orbit around Mars, becoming the first human spacecraft to orbit another planet in the solar system. The probe begins a nearly year-long survey of the red planet, mapping over 70% of its surface at a much higher resolution than was achieved by the previous NASA Mars probes, Mariners 6 and 7. Mariner 9’s mapping mission is temporarily delayed by a global dust storm obscuring the entire planet when the orbiter arrives. Among its discoveries are Olympus Mons, the solar system’s largest volcano, and the gigantic canyon later named Valles Marineris. Mariner 9 also gathers images of Mars’ two moons, Phobos and Deimos.