Mars - The Viking Mission

Within only four years NASA went from orbiting Mars to a landing on the planet. In 1976 the Viking mission was the first American spacecraft to land safely on Mars. For the mission NASA built two identical spacecraft, each containing an orbiter and lander. The two spacecraft entered orbit around Mars and released their landers to descend to the planet's surface.

The spacecraft launched only weeks apart during late summer 1975. It took them nearly a year to reach Mars. On July 20, 1976, the Viking 1 lander set down on the western slope of Chryse Planitia (the Plains of Gold). On September 3, 1976, the Viking 2 lander set down at Utopia Planitia (the Plains of Utopia).

The landers provided NASA with constant weather reports. They detected nitrogen in the atmosphere. Scientists reported that a thin layer of water frost formed on the ground during the winter near the Viking 2 lander. Temperatures varied between minus 184 degrees Fahrenheit in the winter to 7 degrees Fahrenheit in the summer at the lander locations.

The orbiters mapped 97 percent of the Martian surface and observed more than a dozen dust storms. Scientists examined Viking images and decided that some geologic features on Mars could have been carved out millions of years ago by flowing water. The Viking 2 orbiter continued functioning until 1978. The Viking 1 orbiter lasted another two years. The Viking1 lander continued to make transmissions to Earth until 1982.

The landers were unique because they were powered by generators that created electricity from heat released during the natural decay of plutonium, a radioactive element. This method of power generation was selected because NASA feared that sunlight on the planet would not be consistent enough to provide solar power.

The Viking orbiters carried high-resolution cameras and were able to map atmospheric water vapor and surface heat from orbit. The landers included cameras and a variety of scientific instruments designed to investigate seismology, magnetic properties, meteorology, atmospheric conditions, and soil properties. They also tested for the presence of living microorganisms in the soil, but found no clear evidence of them. They did learn that the surface of Mars contains an iron-rich clay. The Viking images revealed that Mars has a light yellowish-brown atmosphere due to the presence of airborne dust. In other words, the Red Planet is actually more the color of butterscotch.

Many scientists associated with the Viking project concluded that Mars is "self-sterilizing." This means that the natural planetary conditions are such that living organisms can not form. The high radiation levels and the unique soil chemistry are actually destructive to life. The Martian soil was found to be extremely dry and oxidizing. Oxidizing agents destroy organic chemicals considered necessary for life to form. The self-sterilizing theory was not universally accepted, however, and remains controversial.