Recent results from the Viking labeled release experiment on Mars

Additional results have recently been obtained from the Labeled Release (LR) life detection experiment on Mars. On Viking Lander 2 an experiment using surface material obtained from under a rock shows a response essentially identical with those obtained from other surface samples. Further, after a second nutrient injection, there is an initial drop in the level of radioactive gas present in the test cell, followed by a slow, gradual evolution of radioactivity over the long incubation period. This gas evolution, which proceeds at a rate declining with time, attains a final level similar to that seen just prior to second injection. Following completion of this experimental cycle a fresh Martian surface sample was heat sterilized for 3 hours at 46°C prior to nutrient injection. The resultant evolution of radioactive gas is substantially reduced in agreement with results reported previously. These results are consistent with a biological response and also greatly narrow the number of possible chemical reactants. The current status of the Labeled Release experiment on Mars is summarized.