Starting in the mid-1960's, the American space program attempted to get clearer and closer glimpses of the Martian surface. By the time of Mariner 9, three previous probes had been there and tried that; appetites whetted, scientists raised their standards and their expectations.
The three previous missions--Mariners 4, 6 and 7--were designed mainly to photograph the surface of Mars and its moons. Now scientists turned to an intense study of Mars, the planet. Mariner 9 was launched in May 1971 on a mission to orbit Mars. Never before had a spacecraft orbited another planet. Would NASA fly it into Mars's atmosphere at the correct speed? Would it achieve a stable orbit around Mars? Or would it skip off Mars's atmosphere like a stone skimming across the surface of a pond?
To NASA's relief Mariner 9 successfully orbited Mars after a journey of 167 days. While Mariner 9 was surveying the planet, Mars was experiencing a global dust storm. This storm, which was the undoing of the Soviet Mars 2 and 3 missions, almost completely obscured the dusty surface. Only one feature--the crater atop the 15 mile high volcano Olympus Mons--showed above the dust. Fortunately the dust storm subsided while Mariner 9 was still in orbit, so its pictures helped determine a landing site for the later Viking missions.
Mariner 9 did surprise NASA with some photographs. Some photos showed what appeared to be wandering tributary channels suggesting that liquid water may have once existed on Mars. As Mariner 9 orbited Mars, it became evident that it was going to outlive its expected lifespan. Mariner 9 travelled around Mars 698 times in less than a year, far surpassing all expectations of the spacecraft. Mariner 9 traveled around Mars twice a day... besting H. G. Wells's record for going around the world in 80 days!
Photo. Photo of the Mariner 9 spacecraft. Courtesy of NASA, JPL.
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