Brief Synopsis
The pyrolytic release experiment (PR) is based on the assumption that terrestrial life synthesizes organic material from carbon dioxide (CO₂) and carbon monoxide (CO).  This experiment called for the incubation of a soil sample with radioactively marked CO2 and CO and the subsequent measurement of radioactive particles in the soil afterward.  This experiment also produced unexpected results, which proved to conclude that either there was no life or if there were life, it did not assimilate the CO2 and CO.  Once again, making more restrictions on the sample type tested could solve the main problems of this experiment. 

Equipment

-         Viking composite instrument including ¹⁴C detector

-         CO₂ labeled with ¹⁴C

-         Source of krypton to pressurize the chamber

-         Heat source

-         Light source (xenon arc lamp)

Protocol

n      place .25 cc of soil in the soil chamber

n      add 20mL of radioactively labeled CO₂ and CO

n      add krypton to pressurize the chamber

n      incubate the sample under xenon arc lamp for 120 hours (5 days)

n      flush sample of atmosphere and heat to 635°C to pyrolyze any organic material

n      run organic material (gases) through ¹⁴C detector

The incubation under the lamp is to maximize the assimilation of the radioactive carbon compounds into any organic material of the soil.  The wavelength of the xenon lamp was constrained to over 320nm to ensure the absence of any nonbiological, photocatalyzed synthesis of organic compounds from the CO and CO₂.

Viking results

The data show that a fixation of atmospheric carbon occurs in the surface material of Mars under conditions approximating the Martian ones.  Although the amount of material was small relative to that which organisms on Earth produced, it was still more significant than the margin of error. 

Problems

Due to the lack of organic material as detected by the GC/MS, the probability of there existing such organic material was slim and made the results hard to believe.  In addition, the argument was brought up that any Martian organisms would have been killed under the lamp energy as it provided heat that greatly exceeded its normal climate while the sample tested positive after being heated. Therefore, the material detected must have been the product of the nonbiological reactions.  Other alternate explanations for the results include the carry-over of any particulate matter from the incubation chamber to the column between the chamber and the ¹⁴C detector and the incorporation of the radioactively marked CO into a carbon polymer that existed on the Martian soil.  Another explanation is related the existence of peroxides and superoxides; the CO could have been reduced by H₂O₂ to produce the organic material that the detector was testing for.

Alterations made to protocol

While this experimental protocol is more conservative than others, it still needs to be narrowed down to specific types of soil.  Basically, the conditions for the soil are the exact same as the conditions mentioned for the labeled release experiment.  By imposing those conditions, we can successfully eliminate most of the problems and uncertainties.  Furthermore, we can test the suggested soil sample to ensure that no other inorganic molecule such as H₂O₂ and the carbon polymer interfere with the successful assimilation of the carbon.

Sources

Levin, Gilbert V. and Patricia Ann Straat, “Recent Results From the Viking Labeled Release Experiment on Mars.” Journal of Geophysical Research. Vol. 82, No. 28 September 30, 1977

Carr, Dr. Michael H. and Benton Clark et al. “An Exobiology Strategy for Mars Exploration.” Online: http://cmex.arc.nasa.gov/MarsNews/mars_papers/Docs/mars_strat.html 

NASA, “Science on Mars.” Online: http://history.nasa.gov/SP-4212/ch11-5.html

Caplinger, Michael. “Life on Mars.” Online: http://barsoom.msss.com/http/ps/life/life.html

For a handy semi-animation of this experiment, go to http://cybooks.com/ahill3/hill03.html