BOX 1.1 Viking’s Approach to Bioload Reduction

Viking employed a twofold approach to controlling the population of terrestrial organisms that might find their way to Mars. First there was a careful cleaning of the spacecraft, and then the bioload was reduced still further by heat sterilization.

Presterilization

The Viking landers were assembled in Class 100,000 clean rooms. During assembly, thousands of microbial assays were conducted, and these established that the average spore burden per square meter was less than 300 and the total burden of spores on the lander’s surface (i.e., the exposed exterior and those parts of the interior communicating directly with the exterior) was less than 300,000.14 The spore-forming microbe Bacillus subtilis was used as the indicator organism in the microbiological assays on the basis of its enhanced resistance to heat, desiccation, and radiation.

Sterilization

Once the landers had been assembled and sealed inside their bioshields, their bioload was further reduced by dry heating. The landers were heated at a humidity of 1.3 mg/liter such that at the coldest point a temperature of 111.7 °C was maintained for some 30 hours. In other words, much of the lander was subject to a higher temperature for a longer period of time. Once sterilized, the landers were no longer accessible for additional microbial assays. Thus the efficacy of the sterilization procedure was estimated indirectly on the basis of the known heat-survival characteristics of B. subtilis and was credited with reducing the lander’s bioburden by a factor of 104.

REFERENCES

1 A.G. Haley, “Space Law and Metalaw—A Synoptic View,” Proceedings of the VIIth International Astronautical Congress, Rome, Italy, 1956.

2 For a recent discussion of panspermia see, for example, Paul Davies, “Interplanetary Infestations,” Sky & Telescope, September 1999, page 33.

3 United Nations, Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies, U.N. Document No. 6347, January 1967.

4 United Nations, Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies, U.N. Document No. 6347, January 1967.

5 See, for example, L.B. Hall and R.G. Lyle, “Foundations of Planetary Quarantine,” L.B. Hall (ed.), Planetary Quarantine, Gordon and Breach, New York, N.Y., 1971, page 5.

6 Space Studies Board, National Research Council, Biological Contamination of Mars: Issues and Recommendations, National Academy Press, Washington, D.C., 1992.

7 D.L. DeVincenzi and P.D. Stabekis, “Revised Planetary Protection Policy for Solar System Exploration, ” Advances in Space Research 4: 291, 1984.

8 Space Studies Board , National Research Council, Biological Contamination of Mars: Issues and Recommendations, National Academy Press, Washington, D.C., 1992.

9 Space Studies Board, National Research Council, Biological Contamination of Mars: Issues and Recommendations, National Academy Press, Washington, D.C., 1992, page 47.



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