The Mariner 9 probe to Mars provided NASA with interesting photographs and atmosphere, temperature and surface composition measurements..

Even while Mariner 9 was still orbiting Mars, NASA was already working hard on the next big step, a landing on the Martian surface. The mission was named Viking. Each Viking spacecraft would consist of two parts - an orbiter and a lander.

The first soft landing on Mars occurred July 20, 1976 when the Viking 1 probe landed. The spot chosen was the Chryse Planitia region, a broad and smooth basin on Mars north of its equator. The first pictures of Mars taken from the surface showed a landing site littered with rocks of all sizes. One rock 10 feet in diameter, big enough to flip over the lander if it had come down on top of it, lay only 25 feet (7.6 m) away. The rock was later nicknamed "Big Joe". Small sand dunes, in addition to the rocks, could be seen in the distance.

Meanwhile, back in space, Viking 2 which had been launched 3 weeks later, was making its approach. It followed Viking 1 into orbit on August 7th and to the surface on September 3, 1976, in the Utopia Planitia region, 4000 miles ( 6,437 km) west of the Viking 1 site. Both Viking landers were now at work on Mars while their companion orbiters circled the planet from above.

Studies of the Martian atmosphere and weather were an essential part of the Viking mission. A small weather station arm extended upward to sample the Martian winds. Low temperatures will plunge to below minus 122^o F (50^o C), the high temperature will climb to -22^o F (-30^o C) in midafternoon. Barometric pressure was 7.70 millibars (about 1/125 the air pressure on Earth).

In addition to temperature and air pressure differences, scientists were also surprised to learn of the many similarities between the Martian atmosphere and Earth’s. The daily temperature of both planets peaks at about 3:00 p.m. local time. The day to night temperature ranges at both lander sites are similar to the temperature ranges in deserts on Earth, though Mars is colder. Winds over the Martian plains seem to follow the same patterns as winds on the Great Plains in the United States. Both planets have clouds and fog.

Viking 1 stood on the Martian surface for eight days before the search for life began in earnest. The question of life would be up to the complex miniature science laboratories hidden in the lander’s interior.

Three life experiments were sent to Mars on Viking. The first would check to see if carbon dioxide was being taken in and converted into organic(carbon-based) compounds. On Earth, plants do this. The second experiment would check to see if certain gases were being given off, as they are by organisms on Earth. Finally, a special radioactive "food" solution was fed to a third sample to see if radioactive carbon dioxide gas was expelled. If so, that gas could be detected.

At first, scientists were elated at the results. In each experiment, something was going on that could be interpreted as the action of living things. But then, a chemical analysis experiment failed to detect any organic compounds (carbon-based chemicals that make up living things). They couldn’t understand why lifelike reactions were taking place when no other signs of organisms, living or dead, could be detected. Eventually, scientists achieved similar results with non-living materials. The exotic chemical reactions only mimicked life. The question "Is there life on Mars?" was left unanswered.

The Viking missions were important.  They served as the fundamental framework for future Mars efforts.

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