<title>The Viking Labeled Release experiment and life on Mars</title>

Abstract

The Labeled Release (LR) life detection experiment aboard NASA's 1976 Viking Mission reported results which met the established criteria for the detection of living microorganisms on the soil of Mars. However, a variety of reasons led to the consensus of involved scientists that the positive responses at both Lander sites were caused by a chemical agent in the soil and not by microorganisms. In the years since Viking, new information from Mars and Earth has come to bear on this issue. Perhaps most spectacular are the analyses of SNC meteorites ALH84001 and EETA79001. The Viking LR experiment and each of the major chemical theories that have been proposed to explain it are reviewed in the context of these post-Viking developments, together with some Viking data hitherto unapplied to this important issue. Each of the theories attributing the LR results to chemistry is shown to have one or more key defects. It is concluded that the Viking LR experiment detected living microorganisms in the soil of Mars. Recommendations for confirming this conclusion in the near future are given.