Biological implications of the Viking mission to Mars

Viking mission studies of the Martian environment are described, and it is concluded that the conditions now known to exist at and below the Martian surface are such that no known terrestrial organism could grow and function. Concentrations of water vapor, ice, liquid water, reduced carbon, and organics are estimated, biological experiments are discussed, and possible nonbiological explanations for the results of the biological experiments are considered. The studies show that elements essential to terrestrial biology are present although no organic compounds or liquid water were detected. It is suggested that powerful oxidants at the surface are responsible for the release of oxygen by soil moistened with water vapor and also for the decarboxylation of organic nutrients. The mechanism of organic synthesis by soil samples is not known. It is thought that the Martian environment in the past might have permitted the origin and transient establishment of a biota.