Two probes named Viking were launched from Earth in 1976, each with an orbiter that would travel around the planet and photograph the surface and with a lander that would settle down on the surface and analyze soil samples.
How did NASA plan on finding life on Mars? Initial ideas for the missions involved equipping Viking with a long, plastic cable that carried an electrical charge. This would shoot out of Viking, like a snake's tongue, to taste the air and soil around it. This idea was rejected, however, because a mechanical scoop could not only perform the same experiments but also carry useful instruments as well.
Photo. The landing site of Viking 1. Courtesy of NASA, JPL.
A small scoop dug into the Martian soil, gathered up a sample, and deposited it into a little bin, where several experiments would be performed to test the soil for signs of life. Scientists based their experiments on the assumption that the most abundant form of life would probably be a form of bacteria, as this is the most common type here. The three experiments were the pyrolytic release, the gas exchange, and the label release experiments.
In the pyrolytic--a word that refers to the chemical decomposition of something by the application of heat--release experiment, a soil sample was incubated at 45 degrees Fahrenheit in a Martian-like atmosphere for five days. On the fifth day, the temperature was increased to 1,150 degrees F. The gases given off were swept by a helium purge into a vapor trap, in an attempt to catch any organic molecules into carbon dioxide. Then they passed through a radioactivity detector. If the radioactivity count were high, it could mean that the carbon dioxide had once been used for life. This was performed to find if any existing organisms could change carbon dioxide into the organic compounds that would serve as the organism's body. If any organisms did exist they would breathe out gases that would change the atmosphere in the chamber.
Photo. The Viking 1 lander is shown here with its soil scoop arm extended. Courtesy of NASA, JPL.
In the gas exchange experiment, NASA scientists wanted to determine whether anything in the soil would give off gases. All organisms on Earth do, so this could be a fairly safe assumption for all forms of life. The soil sample was incubated for seven days under an atmosphere of helium, krypton, and carbon dioxide, mixed with either water vapor or other nutrients. After these were added, fractions of the atmosphere were analyzed to find the presence of metabolic activity.
Photo. A close-up of the Viking biology processing center that handled the soil samples; each of the probe's biology laboratories cost $50 million dollars and each included 40,000 individual mechanical parts. Courtesy of NASA, JPL.
The third experiment centered on the fact that all animals, including humans, on Earth consume organic compounds and give off carbon dioxide. In the label release experiment, a soil sample was incubated for eleven days under normal Martian atmosphere conditions with a dilute solution of nutrients labeled with radioactive carbon. The atmosphere surrounding it was monitored for any release of radioactive carbon dioxide. A positive result would indicate the presence of metabolizing cells.
Photo. The landing site of Viking 2. Courtesy of NASA, JPL.
On September 3, later the same year, Viking 2 landed on Utopia. It performed the same experiments and got the same clouded results. The three biology experiments discovered chemical activity in the soil, but provided no clear evidence for the presence of living microorganisms. There were no organic chemicals, no carbon compounds, the basis for all life on Earth. Overall, it seemed that life could be present on Mars. But were these results caused by living creatures, or by a chemical reaction in the soil itself?
Mission to Mars. An educational site created for the ThinkQuest contest.