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METABOLISM. Terrestrial life breaks down and uses nutrients and releases waste products and gases, a process called metabolism. Viking will attempt to determine whether any Martian organisms do the same thing, by means of a study called the labeled-release experiment. A sample of Martian soil will be loaded into a test chamber, then moistened with a substance scientists have named "chicken soup," a nutrient broth rich in vitamins and amino acids and containing radioactive carbon 14. The sample will then be incubated at a temperature of 47° F. for up to eleven days. During the experiment, any organism that functions by metabolism is likely to consume the nutrient and release gases that contain radioactively labeled wastes. Viking's sensors are capable of detecting them.
RESPIRATION. Living organisms on earth alter their environment as they live, breathe, eat and reproduce. To determine whether Martian organisms do likewise, Viking will conduct a third experiment, called gas exchange. It will submerge a soil sample in a liquid nutrient, then incubate the dirt for up to twelve days in an atmosphere of helium, krypton and carbon dioxide. The lab will then sample the atmosphere in the chamber at regular intervals, searching for the gases generally produced during the processes of life—molecular hydrogen, nitrogen, oxygen, methane and carbon dioxide.
Should Viking find any indications of growth, metabolism or respiration in the soil of Mars, the excitement—and the implications of the discovery—will be unprecedented. The existence of even the most rudimentary Martian organism would prove that the evolution of life on earth was not an isolated occurrence. Indeed, it would strongly suggest what many scientists already believe: life is commonplace in the universe. In the Milky Way galaxy alone, for example, there are probably hundreds of millions of sunlike stars, many with planets capable of harboring life. If life exists on both earth and Mars, the odds are good that it has evolved on other planets too.
Even if the Viking landers fail to detect living organisms, the possibility of life on Mars will not be precluded. With the Viking biological package, says Carl Sagan, "we simply may be asking the wrong questions." In other words, the experiments can tell only if there is earthlike life in the particular soil samples. Martian life could be based on a chemistry completely different from that on earth. Then, too, Viking, which landed on a site selected more for safety than scientific value, could simply be looking in the wrong part of the planet. The lander does not move and thus cannot tell what may lie even over the nearest hill.
Whatever the additional findings of Viking 1, and of Viking 2 afterward, the billion-dollar project has already paid off handsomely—and, in a way, has even provided what it set out to find. For, as Science-Fiction Writer Bradbury says, "From this point on, there is life on Mars—an extension of our sensibilities. Man is reaching across space and touching Mars. Our life is on Mars now."
*In contrast to the lunar sky, which, because the moon has no atmosphere, looks black.
*Equivalent to terrestrial air pressure at an altitude of 100,000ft.