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2 Binary Decision Trees
Pages 13-18

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From page 13...
... To accommodate new knowledge about extremophiles on Earth, the Europa report study committee increased the model complexity by using different bioload reduction factors for physiologically distinct classes of microbes, including non-specialized microbes, bacterial spores, radiation-resistant spores, and highly radiation resistant non-spore-forming microorganisms. The 2000 Europa report acknowledged that its improved methodology continued to rely on the uncertain nature of values for nearly every factor in a chain of "uncorrelated" factors: "The values assigned to individual parameters are not definitive.
From page 14...
... Alternatively, underestimates of bioload reduction coupled with overestimates of bioload on the spacecraft and the flawed assumption that any organism delivered to the target body will grow (Pg = 1) , would impose unnecessary and possibly unachievable planetary protection demands.
From page 15...
... 3 Deep-sequencing surveys suggest that microbial diversity may be 1,000 to 10,000 times greater than estimates from cultivation-based studies and that most of this novelty corresponds to low-abundance taxa described as the "rare biosphere." 4,5 Similar analyses of simple mock communities containing one or a few taxa suggested that sequencing errors can lead to inflated estimates of micro bial diversity.6 More recent studies show that a 2 percent single-linkage preclustering methodology followed by an average-linkage clustering based on pair-wise sequence alignments more accurately predicts expected complexity of mock communities of known taxonomic composition. However, this analytical paradigm does not reduce the fraction of novel taxa in the long-tailed rank abundance curves that define the rare biosphere for complex, naturally occurring microbial communities.
From page 16...
... apply to the simplified formulation adopted as official COSPAR policy. For example, current technology, including the NASA standard spore assay and culture-independent molecular technologies, displays a wide variance over many orders of magnitude when estimating bioburden at launch (factor 1 above)
From page 17...
... components to 60°C for 5 hours, No and molecular bioload analysis Stringent planetary protection required: NASA standard cleaning and bioload monitoring, molecular bioload analysis, and Viking-level, terminal bioload reduction; OR cancel mission FIGURE 2.2 Binary decision-making framework for planetary protection of icy solar system bodies. "Yes" answers to Decision Points 1-6 release the mission from rigorous planetary protection procedures, whereas a "Yes" to Decision Point 7 requires moderate heating of sealed components.
From page 18...
... , the probability of transporting terrestrial organisms to a habitable environment on a given target body, and the ability of terrestrial organisms to endure bioload reduction treatments and subsist in non-terrestrial environments. Recommendation: Approaches to achieving planetary protection should not rely on the multiplica tion of bioload estimates and probabilities to calculate the likelihood of contaminating solar system bodies with terrestrial organisms unless scientific data unequivocally define the values, statistical variation, and mutual independence of every factor used in the equation.


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