Recent results from the Viking Labeled Release Experiment on Mars

Abstract

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.

On the ability of the Viking gas chromatograph–mass spectrometer to detect organic matter

“…This was clearly stated in all published descriptions of the instrument and of the results obtained during the mission (1)(2)(3)11). The search for microbial life was the subject of three separate Viking biology experiments (12)(13)(14). The misconception presently prevailing in the astrobiology community and literature is probably caused by the effect the results from the Viking GCMS had on the interpretation of the data from these biological experiments.…”

The limitations on organic detection in Mars-like soils by thermal volatilization–gas chromatography–MS and their implications for the Viking results

“…The lack of organics in the martian soil could also be explained by their oxidation to carbon dioxide due to the presence of such oxidants and͞or direct UV radiation damage (8). There have been many suggestions regarding the nature of the chemical reactivity of the martian soil, but no laboratory experiment has yet been able to simulate both the gas exchange (3) and the LR response (5 have not yet performed in situ experiments on Mars. Mars Oxidant Instrument has been successfully tested in the Mars-like soils of the Atacama Desert, where the oxidative nature of the soil is thought to be triggered by strong acids (e.g., sulfuric and nitric acids) depositing from the atmosphere (9).…”

“…The biological tests consisted of three independent experiments designed to detect Earth-like microorganisms in the top few centimeters of the martian soil. The gas exchange experiment was designed to determine whether martian life could metabolize and exchange gaseous products in the presence of water vapor and in a nutrient solution (3); the carbon assimilation experiment was based on the assumption that martian life would have the capability to incorporate radioactively labeled carbon dioxide and͞or monoxide in the presence of sunlight (i.e., photosynthesis) (4); and the labeled release (LR) experiment sought to detect heterotrophic metabolism by the release of radioactively labeled carbon initially incorporated into organic compounds in a nutrient solution (5). At both Viking landing sites the three biological experiments yielded positive responses demonstrating the presence of a highly reactive soil.…”

Astrobiology and the Possibility of Life on Earth and Elsewhere…

“…Therefore, the conclusion was drawn that no organic compounds of Martian origin were detected (Biemann et al 1976(Biemann et al , 1977. This null result strongly influenced the interpretation of the reactivity seen in the Viking biology experiments (Levin and Straat 1977, 1979. It led to the conclusion that life was not present and, instead, that there was some chemical reactivity in the soil (Biemann 1979;Klein 1977).…”