Biological Contamination of Mars Issues and Recommendations (1992) / Chapter Skim
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5 ASSESSMENT OF THE 1978 REPORT
5 ASSESSMENT OF THE 1978 REPORT
Pages 43-50
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From page 43... ...
of a terrestrial microorganism on each of the planets. There was some difficulty in arriving at a sensible and useful Pg, necessitating that the 1978 committee be charged with the task of comprehensively evaluating Pg based on available knowledge of the physical and chemical properties of the surface and atmosphere of each planet and conditions that limit life as we know it.
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From page 44... ...
The committee recommended a Pg of less than 10-10 for the subpolar regions of the planet within 6 centimeters of the surface, less than 10-8 for subsurfaces in subpolar regions, and less than 10-7 for the polar ice caps. These ranges for Pg values reflect Viking data for subpolar regions, including those results that indicated the presence of strong oxidants, observed organic compounds, water, and the possibility that liquid water could exist seasonally and diurnally at the polar caps.
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From page 45... ...
• Category IV missions are certain types of missions (mostly probe and lander) to a target planet of interest for understanding chemical evolution and/or the origins of life, or for which scientific opinion suggests a significant chance of contamination that could jeopardize future biological experiments.
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From page 46... ...
.3 Comments and estimates made by the contributors point to Pg values for terrestrial organisms on Mars that are probably lower than the 1978 estimates. Their consensus was that an exceedingly small Pg was necessitated by the low probability of liquid water existing on Mars and the low probability of an appropriate terrestrial organism occupying a particular martian environment and growing there.
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From page 47... ...
Although some progress toward quantification of Pg could perhaps be realized in welldesigned laboratory simulation experiments, the task group is not optimistic that the central question of the presence and duration of a liquid water phase in the near-surface martian regolith environment can be unambiguously addressed without more information obtainable possibly only from in situ measurements on Mars itself, or from returned samples -- or conceivably from neither.
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From page 48... ...
(The task group notes that appropriate laboratory simulation experiments to evaluate these probabilities for candidate microorganisms are entirely feasible, since both the spacecraft geometry and the characteristics of its space environment can be well determined.)
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From page 49... ...
The task group emphasizes that the philosophical intent of the 1978 committee to protect Mars from terrestrial contamination so as not to jeopardize future life-detection experiments on Mars is still profoundly important. Recommendation 1 above deals with the issue of contamination by nonviable but intact cells and biochemical components from terrestrial organisms, independent of whatever low Pg value they may have.
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From page 50... ...
1991. Planetary Protection Issues for the MESUR Mission: Probability of Growth (Pg)
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