After Mariner 9's global mapping of Mars in the early 1970s, the next step in exploration was to land on the planet and look for life. On August 20, 1975, NASA launched the first of two Mars lander missions: the Vikings. The Viking project was managed by James S. Martin at NASA's Langley Research Center in Hampton , Virginia . Each Viking mission consisted of an orbiter/lander pair. JPL's task was to build and manage the orbiters and operate the missions from Pasadena . Martin Marietta Corporation's plant in Denver , Colorado , built the landers.
JPL's orbiters were modified and enlarged versions of the Mariner 9 spacecraft, and they carried the landers encased in their aeroshells. After the spacecraft reached Mars orbit, mission scientists studied high-resolution images returned by orbiter cameras to make sure the pre-selected landing sites were safe. This was risky too, since the orbiters' cameras could only see objects down to the size of a football stadium. But even a two-meter-diameter (almost seven-foot-diameter) rock was large enough to destroy a lander! In both cases, the landing site had to be changed after arrival, delaying the first landing from its original July 4th date.
Viking 1's lander finally reached the surface successfully on July 20, 1976; Viking 2's lander descended safely on September 3, 1976.
The nuclear-powered landers carried instruments for meteorology, seismology, magnetic studies and imaging. They also carried a set of biological experiments intended to detect life. The life detection experiments were the most popular aspect of the Vikings and the most controversial. The results were ambiguous. JPL's director, Bruce Murray, believed that the experiments had shown the surface was so oxidizing that it was self-sterilizing, meaning nothing could grow there. A minority of Murray's colleagues disagreed. No further life-oriented experiments have reached Mars as of 2006, so this controversy is unresolved.
The Viking orbiters largely did resolve the question of where Mars' water had gone. JPL's Barney Farmer had built a Mars Atmospheric Water Detector experiment for the orbiters, which he used to map the distribution of water vapor in Mars' thin atmosphere. Its data suggested that the water was frozen into the Martian surface just as permafrost is on Earth. Murray 's geology team drew similar conclusions based on the orbiters' four years of imagery. It would be another 25 years before these findings could be confirmed by the Mars Odyssey mission.
Olympus Mons, the largest volcano in the solar system. + Full image
A thin coating of water ice can be seen on rocks in this Viking 2 lander image. + Full image
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