Mariner 9 was launched May 30, 1971. It is the first man-made satellite to orbit another planet. The Mariner 9 mission was intended to last 90 days and map 70% of the Martian surface; however, the probe was operational for almost a year. During this time, Mariner 9 completed 698 revolutions about Mars and mapped almost all of its surface. Over 7000 TV images were returned, including pictures of both Phobos and Deimos. Mariner 9 was intended to have been one of a pair of Mars orbiters, but the Mariner 8 spacecraft failed before it even reached Earth orbit. Therefore, Mariner 9's mission was changed slightly in order to recover at least part of the data which Mariner 8 would have gathered. A planet-wide dust storm delayed the start of the mapping. The images which were returned showed many surprising surface features. They revealed huge volcanoes and calderas as well as the chasm Valles Marineris. In addition, potential Viking landing sites were surveyed. Though the spacecraft is no longer operational, it will probably remain in orbit for at least 50 years after the mission.
