Mariner 9 was a NASA space probe orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 and reached the planet on November 14, of the same year, becoming the first spacecraft to orbit another planet. After months of sandstorms it managed to send back surprisingly clear pictures of the surface.
Mariner 9 was the first spacecraft to orbit another planet. It carried an instrument payload similar to Mariner 6 and 7, but, because of the need for a larger propulsion system to control the spacecraft in Mars orbit, it weighed more than Mariners 6 and 7 combined. When Mariner 9 arrived at Mars, the atmosphere was so dusty that the surface was obscured. This unexpected situation made a strong case for the desirability of studying a planet from orbit rather than merely flying past. Mariner 9's computer was thus programmed from Earth to delay imaging of the surface for a couple of months until the dust settled. After 349 days in orbit, Mariner 9 had transmitted 7,329 images, covering over 80% of Mars' surface. The images revealed river beds, craters, massive extinct volcanoes (such as Olympus Mons, the largest known volcano in the Solar System), canyons (including the Valles Marineris, a system of canyons over 4,000 kilometers [about 2,500 miles] long), evidence of wind and water erosion and deposition, weather fronts, fogs, and more. Mars' tiny moons, Phobos and Deimos, were also photographed. The findings from the Mariner 9 missions underpinned the Viking program.
Mariner 9 was designed to continue the atmospheric studies begun by Mariners 6 and 7, and to map over 70% of the Martian surface from the lowest altitude (1500 kilometers [about 900 miles]) and at the highest resolutions (1 kilometer per pixel to 100 meters per pixel) of any previous Mars mission. An infrared radiometer was included to detect heat sources as evidence of volcanic activity. Mars' two moons were also to be analyzed. Mariner 9 more than met its objectives.
The ultraviolet spectrometer aboard Mariner 9 was constructed by the Laboratory for Atmospheric and Space Physics.