NASA's Viking Mission, Pyrolytic Release Experiment, and the Search for Photosynthetic Life on Mars
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NASA's Viking Mission, Pyrolytic Release Experiment, and the Search for Photosynthetic Life on Mars

During Project Viking, scientists tested for the possibility that photosynthetic microorganisms might inhabit Mars. They employed the Pyrolytic Release Experiment (PR) developed by Norman Horiwitz. In a way, the PR was the opposite of the LR.

Viking 1 and Viking 2, launched during the 1970s also played a major role in our exploration of Mars. These two probes were humanity’s first space missions devoted specifically to the search for extraterrestrial lifeforms. They were also the first terrestrial objects to successfully land and function on the surface of another planet, although five years earlier the ill-fated Soviet Mars 3 had managed to reach the Martian surface and survive for a few seconds before her instruments failed. The Viking probes carried several instruments and their findings left scientists faced with a great mystery.

In a way, photosynthesis is the opposite of respiration. In photosynthesis, the carbon contained within CO2 is used to make organic nutrient compounds through a process called reduction, the opposite of oxidation. Photosynthetic organisms can then oxidize the compounds through respiration or they can be saved and/or used by other organisms. Thus, photosynthetic organisms use to CO2 make their own food! In order to do this, they need sunlight and water and as a by product they produce O2, which they can use during respiration in the dark or which can be used by non-photosynthetic organisms –humans for example.

Plants are famous for being photosynthetic but did you know that many microorganisms are also photosynthetic? The picture is an autofluorescence image of the photosynthetic microorganism Microcystis aeruginosa strain PCC 7806 (source Cyanobacterial Image Gallery http://www-cyanosite.bio.purdue.edu/images/images.html)

During Project Viking, scientists tested for the possibility that photosynthetic microorganisms might inhabit Mars. They employed the Pyrolytic Release Experiment (PR) developed by Norman Horiwitz. In a way, the PR was the opposite of the LR. While the LR treated Martian soil samples with 14C-containing liquid nutrients, the PR exposed soil samples to 14C-containing gases, CO2 and carbon monoxide (CO), because both of these gases are present in the Martian atmosphere. After exposure to the gases, the soil was studied to see whether it can taken in any radioactivity, which would indicate that the 14C-containing CO2 and/or CO had been reduced to organic compounds within the soil.

When the PR experiment was performed, very small amounts of carbon from the gases were found to have become part of the soil, indicating reduction. However this occurred in both unheated samples and those heated prior to testing, suggesting that the effect had been the result of some non-living agent/s process in the soil. Also, the small amount of reduction occurred both in the light and the dark and thus the experiment did not detect photosynthesis.

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