Viking pyrolytic release (PR) experiment
Headed by Norman Horowitz, and also known
as the 'carbon assimilation' experiment.1 Of the three Viking
biology experiments, this was the only one to attempt to detect signs of
life in the complete absence of water and organic nutrients. It was assumed
that any organisms on Mars would have developed
the ability to assimilate carbon dioxide
and carbon monoxide from the atmosphere
and convert these, in the absence of water, to organic matter. Therefore,
the PR experiment exposed a small sample of Martian soil to quantities of
these two gases which had been labeled with radioactive carbon-14 for detection
purposes. After 120 hours of incubation under an artificial sun (a xenon
arc lamp), the soil chamber was heated
to about 625°C to break down (pyrolize) any organic matter and release
the volatile organic products for subsequent testing by a radiation counter.
Since any organisms present would be expected to carry out metabolic processes
during which they would take in carbon-14 from the gas in the chamber, detection
of carbon-14 would be a positive result. It would not, however, be conclusively
biological, since a first peak of radioactivity might equally be due to
purely chemical processes. In order to rule out this possibility, other
samples, serving as controls, were sterilized by heating before the carbon
source was admitted.
References
- Horowitz, N. H., Hubbard, J. S., and Hobby, G. L. "The Carbon-Assimilation
Experiment: The Viking Mars Lander," Icarus, 16, 147 (1972).
Related categories
•
MARS
• ASTROBIOLOGY
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