Mariner 9 was also a small robotic spacecraft, and it was launched on May 30, 1971. Unlike Mariner 4, 6, and 7, which simply flew by Mars, Mariner 9 was designed to establish an orbit around the planet. It did so successfully, and continued to orbit for almost a year. Mariner 9 used its imaging instruments to make a map of the entire surface of Mars. As a result, many previously unknown features of Mars were discovered, including Olympus Mons and Valles Marineris, and dry river beds. Close up images were also taken of the two Martian moons, Phobos and Deimos.