Preventing the Forward Contamination of Europa (2000) / Chapter Skim
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A Calculating the Probability of Contamination, Pc
A Calculating the Probability of Contamination, Pc
Pages 29-38
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From page 29... ...
Expressing the 10-4 standard in terms of the delivery of viable organisms to an ocean allows spacecraft designers and mission planners to take advantage of the bioload reduction attributable to the high radiation environment that occurs naturally in transit to Jupiter, in orbit around Jupiter while the spacecraft maneuvers to rendezvous with Europa, in orbit around Europa, and at and near Europa's surface following a controlled or uncontrolled landing. In this context, it is expected that the requirement will be satisfied by meeting a level of bioload reduction prior to launch that depends on the mission plan, with landers or short-lived orbiters requiring a more stringent level of cleanliness than long-lived orbiters.
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From page 30... ...
Type D are a subset of Type A and are also resistant to high radiation doses. To avoid unnecessarily elaborate testing and analysis procedures, the task group suggests that Types C and D be determined by a simple screening test using exposure to 60Co or by some other well-established procedure for dosing with ionizing radiation.
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From page 31... ...
Thus, unsuccessful laboratory cultivation does not imply that the organisms are not viable. Indeed, only 0.2 percent to 0.3 percent of the organisms found in sediments and soils can be cultured using current techniques.6 7 In eutrophic samples of activated sludge, the fraction is not so small,8 9 but in seawater the fraction of successfully cultivated microorganisms is very small.'° I' Because a significant component of spacecraft contamination is known to come from soil (the other major component comes from organisms associated with the human body)
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From page 32... ...
The factor F5 represents the likelihood of landing at a geologically active site on the europan surface. Landing at such a site could allow geologic activity to transport some or all of the spacecraft to a depth sufficient to shield it from the sterilizing effect of the surface radiation environments and eventually allow it to reach a europan ocean.
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From page 33... ...
This conservative value may need to be revised downward if recent suggestions that both hvdrooen Deroxide and sulfuric acid are relatively abundant in Europa's surface ice are confirmed.25 26 .._-, -- - r Fib Availability of Nutrients Elemental nutrients are needed by organisms to synthesize key biomolecules. Especially important are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
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From page 34... ...
The task group took the probability that the entire suite of needed components are present as 50 percent F,c~uitabili~ of Energy Sources If life already exists on Europa, primary production by chemoautotrophs might support a food web that produces organics and hence contains heterotrophic populations. The task group made a few a priori estimates of the likelihood that an Earth microbe, either heterotrophic or autotrophic, would grow in a novel chemosphere or the likelihood that it would displace indigenous microbiota in a novel biosphere.
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From page 35... ...
They indicate that sterilization of a relatively clean spacecraft by the natural radiation environment can be sufficient to protect the europan ocean environment. The task group notes that the 10= standard is met if all portions of the spacecraft receive a radiation dose of 7 Mrad.
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From page 36... ...
9 M Wagner et al., "Development of rRNA-Targeted Oligonucleotide Probe Specific for the Genus Acinetobacter and Its Application for In Situ Monitoring in Activated Sludge," Applied Environmental Microbiology 60: 792, 1994.
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From page 37... ...
~9 C Lange et al., "Construction and Characterization of Recombinant Deinococcus radiodurans for Organopollutant Degradation in Radioactive Mixed Waste Environments," Nature Biotechnology 16: 929, 1998.
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From page 38... ...
J.T.C. Grotenhuis et al., "Bacteriological Composition and Structure of Granular Sludge Adapted to Different Substrates," Applied Environmental Microbiology 57: 1942, 1991.
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