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5 The Sterilization of Samples from Mars
Pages 39-46

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From page 39...
... It is essential that a means be found to safely remove aliquots of the samples from the quarantine facility and distribute them to qualified members of the international scientific community, so that the full complement of modern scientific instrumentation and individual talents can be brought to bear on the analysis and interpretation of the samples. The prospect of using the large and very sophisticated laboratory instruments available throughout the world for this purpose was the main justification for returning samples to Earth rather than trying to study Mars materials in situ on that planet.
From page 40...
... It is also apparent that there is much uncertainty about the extent of damage caused to organic compounds by sterilizing procedures. One mitigating circumstance is that many of the biomarker compounds can be extracted by thermal desorption and supercritical fluids within the quarantine facility and, pending verification that the procedure effectively sterilizes the extracts produced, the latter can be distributed to laboratories for studies without further treatment (Figure 4.1; see also "The Study of Extracts" in Chapter 4~.
From page 41...
... For the case of dry heat sterilization, one plausible standard is that commonly used in the surgical suites of hospitals. This is a stringent standard because the tools sterilized have come from the hospital environment, a very dirty environment with respect to microbial contamination, and after sterilization they will be inserted into patients with weakened immune systems.
From page 42...
... TABLE 5.3 Some Gamma-ray Irradiation Doses and Their Effects or Applications Dose (Mrad) Effect or Application 0.0003-0.0004 50% killing of human beings exposed and not given medical treatmenta 0.005 Will promptly kill human beings by central nervous system damagea 0.005-0.015 Used to inhibit sprouting of white potatoesb 0.02-0.05 Used for control of mold in wheat flourb 0.02 90% killings of Salmonella typhimurium (potentially pathogenic bacterium)
From page 43...
... h 90% inactivation of minute virus of micel 90% inactivation of the molecules of a typical enzymed Inactivation of HIV-I by a factor of 10-5 to 10-6 man Dose recommended by International Atomic Energy Agency for the sterilization of medical products Sufficient to destroy HIV-I DNA as assayed by PCR° Used to kill insects and decontaminate dry herbs and spicesb Used to sterilize meat frozen and packaged for NASAP NOTE: Some of the values given can serve only as guidelines, since the values for the radiation sensitivity of specific organisms vary significantly in the literature (see van Gerwen, S.J., Rombouts, F.M., van's Riet, K., and Zwietering, M.H.
From page 44...
... ~~ ~4 FIGURE 5.3 "Killing curve" for Deinococcus radiodurans in a state of desiccation, when it is most resistant to gamma radiation. Colonies of D
From page 45...
... (Indeed, orbital simulations show that some martian ejecta immediately enter Earth-crossing orbits, and a portion of that almost certainly is delivered to Earth in less than a few years.3) If this material contained organisms sufficiently resistant to radiation to survive the relatively small dose they received, then Earth already has been infected by those organisms.4 In practice the sterilization dose used should be the minimum dose that will kill everything known, with some extrapolation factor for the possibility of unknown, more resistant, life forms.
From page 46...
... The preceding section in this chapter argued that if there are Mars organisms sufficiently robust to survive a realistic sterilization treatment in the quarantine facility, then some of these resistant organisms also would have survived transit to Earth in meteorites, and our planet already has been infected by them. Thus sample certification as "effectively sterilized" is appropriately based on verifying that the treatment used kills the most resistant known terrestrial organisms, and that the treatment is at least as harsh as that experienced by recent meteorites in Mars to Earth transit.


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