Mariner 9, the final Mars mission in NASA's Mariner series of the 1960s and early 1970s. Mariner 9 was launched successfully on May 30, 1971, and became the first artificial satellite of Mars when it arrived and went into orbit, where it functioned in Martian orbit for nearly a year. Mariner 9 completed its final transmission on Oct. 27, 1972. Upon arrival, Mariner 9 observed that a great dust storm was obscuring the whole globe of the planet. The dust cleared after a month, and the planet was very different than had been expected, with gigantic volcanoes, a grand canyon, and ancient riverbeds. Mariner 9 exceeded all primary photographic requirements by photo-mapping 100 percent of the planet's surface. The spacecraft also provided the first close-up pictures of the two small, irregular Martian moons: Phobos and Deimos.