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Mariner 9A 1031-kg US probe that became the first artificial satellite of another planet when it entered a 12-hour orbit of Mars on Nov. 13 1971. This orbit, ranging in altitude from 1650 km to 17 100 km approximately, allowed Mariner's two television cameras to return 7329 photographs before contact was terminated on Oct. 27 1972. The entire Martian surface was mapped and close-up views were obtained of Mars' two small natural satellites, Phobos and Deimos. Other equipment included infrared and ultraviolet spectrometers, used for atmospheric studies, and an infrared radiometer to measure surface temperatures.
The photographic reconnaissance was jeopardized by a violent planet-wide dust storm that developed in late September 1971. With the exception of four hazy spots, later found to be the summits of the principal Martian volcanoes of the Tharsis Ridge, all surface features were obscured by dust when Mariner 9 arrived. As the dust settled during the following weeks, photographs revealed for the first time the extent of Martian volcanism and the existence of canyons, such as the Valles Marineris, and channels, which suggest that water once flowed on Mars. The changing appearance of the polar caps with the Martian seasons was also followed. See Mars; Mars, surface features.