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VHI. SUMMARY The rate of synthesis of organic molecules by solar ultra- violet radiation in the primitive lunar atmosphere is estimated. The consequent lunar surface density of organic molecules is very high, probably between 1 and 10 gm cm"2. As the lunar atmosphere was dissipated, heat and radiation produced organic molecules of great complexity from the deposited material. Such organic matter would now be situated beneath overlying layers of meteoritic and other surface debris, at a depth of possibly a few tens of meters, although some distribution throughout the dust may be expected. Reports of gas clouds on the lunar surface are discussed and shown to be probably unreliable. However, the observations of Kozyrev, if verified, would be evidence for lunar subsurface or- ganic matter. Kremlin's theory of heat localization by hydrostatic pressure in dust indicates that constant, biologically-optimum temperatures exist at just the level that surviving primitive organic matter is probably localized. Therefore the possibilities of multiplication of terrestrial microorganisms on the Moon and of survival of in- digenous lunar organisms from the early history of the Moon are not as remote as has sometimes been thought. The probability for survival of a terrestrial microorganism, accidentally deposited on the Moon by an impacting lunar probe, is computed. A population of the least radiosensitive dormant anaerobic microorganisms would be totally destroyed in hours if exposed to solar ultraviolet radiation. The resulting organic dissociation products would remain intact for much longer periods of time; 0. 1 to 10 years if the lunar surface magnetic field strength is much less than 10"2 gauss (so that incident solar protons are magnetically deflected), and 104 to 105 years if the field strength exceeds 10"2 gauss. Organisms shielded from solar illumination, perhaps in congealed dust matrix interstices, would survive cosmic radiation and natural radioactivity for 109 years or more. Lunar subsurface temperatures are not too high to impede survival. The possible kinds of lunar biological contamination are then discussed. Because of the small absolute amount of terrestrial organisms and organic matter likely to be deposited by probe, and their separation in depth from indigenous lunar organisms and 40
organic matter, it is improbable that the two will be confused. But the explosive reproduction of only a very small number of terrestrial microorganisms in indigenous organic matter, and the disruption of the ecologies of hypothetical lunar organisms, are remote but non-negligible possibilities. It is recommended that all lunar probes be thoroughly de- contaminated, and that the first soft-landing probes be equipped for chemical analysis and biological plating of subsurface samples. 41