Organic Matter and the Moon, by Carl Sagan (1961) / Chapter Skim
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VI. SURVIVAL OF CONTEMPORARY TERRESTRIAL MICROORGANISMS ON THE MOON
VI. SURVIVAL OF CONTEMPORARY TERRESTRIAL MICROORGANISMS ON THE MOON
Pages 26-33
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From page 26... ...
This problem is directly relevant to the question of biological contamination of the Moon; it also has a bearing on the panspermia or cosmobiota hypothesis, and on the possibility of survival to the present of lunar organisms or their remains, produced in the distant past. There seem to be three major hazards for survival of terrestrial life on the Moon -- temperature, corpuscular radiation, and solar electromagnetic radiation -- which we discuss below.
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From page 27... ...
B Deflection of Incident Charged Particles by the Lunar Magnetic Field Cosmic rays, charged particles emitted by the Sun, and continuous and discrete solar electromagnetic radiation are all incident on the Moon.
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From page 28... ...
D Adopted Fluxes, Mean Lethal Doses, and Absorption Coefficients We now consider the effects of these radiations on terrestrial microorganisms deposited on the lunar surface.
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From page 29... ...
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From page 30... ...
Considering all these points, then, it appears that a conservative estimate for an average mean lethal dose due to ionizing radiation is 107 rep. For the non-ionizing ultraviolet radiation, D has a strong functional dependence on wavelength, corresponding to the wavelength variation of molecular absorption cross-sections.
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From page 31... ...
mean value of D for the wavelength region X.3000 to X.2000 appears to be the value at X.2537; this should be roughly applicable for an ultraviolet black body spectrum with a Wien peak longward of X.3000. The mean lethal dose at X.2537 for the more radioresistant bacteria, such as B
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From page 32... ...
Hence, microorganisms shielded from the Sun, but just beneath the lunar surface will not be killed by cosmic radiation for at least several hundred million years; microorganisms at greater depths will have even longer lifetimes. Similarly, cosmobiota imbedded in, for example, a meteorite would have lifetimes comparable to the age of the Solar System, and under these circumstances the panspermia hypothesis remains tenable.
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From page 33... ...
Molecules shielded from radiative dissociation would be relatively unaffected by lunar temperatures, and if lodged beneath a few centimeters of insulating lunar surface material, would have lifetimes determined by the cosmic ray flux and natural radioactivity.
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