Organic Matter and the Moon, by Carl Sagan (1961) / Chapter Skim
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II. PRODUCTION OF ORGANIC MATTER IN EARLY LUNAR HISTORY
II. PRODUCTION OF ORGANIC MATTER IN EARLY LUNAR HISTORY
Pages 2-18
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From page 2... ...
However, the newly- synthesized molecules, having greater ultraviolet absorption cross sections than their precursors, were more readily photodissociated; a crucial datum is then the comparison between Id. the mean time for synthesized molecules to diffuse to atmospheric depths which are optically thick in the photodissociating ultraviolet, andTa, the mean time between successive absorptions of photodissociating photons.
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From page 3... ...
After the clearing out of interplanetary space, hot exospheres established in the protoplanetary atmospheres led to efficient evaporation of the planetary envelopes, a process aided by the long mean free paths in interplanetary space and the low escape velocities (due to smaller mass/radius ratios for the protoplanets than for the present planets)
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From page 4... ...
8 years. After the evaporation of these protoatmospheres, and the origin of the secondary lunar atmosphere, the secondary atmosphere was maintained for a period of time discussed in section II F, at sufficient density to absorb all incident solar radiation shortward of K2400.
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From page 5... ...
Whatever the primary laboratory absorber turns out to be, the same molecule is expected to exist in the primitive lunar atmosphere, and the same quantum yields should be applicable. However, these two cases have somewhat different consequences for the question of diffusion, and we distinguish them in the following discussion.
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From page 6... ...
We then have for the time for the synthesized molecule to diffuse from unit optical depth in the longest effective synthesizing wavelength (here~X.2600) to unit optical depth in the longest photodissociating wavelength (here X .
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From page 7... ...
< 3200 A, must have been less than about 1011 photons cm"2 sec"1. We will show in section II E that at no time in the history of the later solar nebula, the lunar protoatmosphere, or the secondary lunar reducing atmosphere was the solar ultraviolet flux so low.
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From page 8... ...
Thus, regardless of the nature of the principal absorbers in the near ultraviolet, it appears that for such molecules as amines, nitriles, saturated hydrocarbons, and some unsaturated hydrocarbons, photolysis was evaded in the early lunar envelopes. For molecules with ultraviolet absorption at longer ultraviolet wavelengths, such as aldehydes, ketones, aromatics and some unsaturated hydrocarbons, a smaller fraction of those synthesized survived.
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From page 9... ...
. Solution of the synthesized molecules in water corresponds to the last step of contemporary laboratory experiments which produce amino acids and other organic molecules from mixtures of reducing gases.
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From page 10... ...
and the photon fluxes derived in the following section, it is easy to see that for all reasonable temperatures and densities at the synthetic level of the primitive lunar envelopes, the time between collisions is much shorter than the time between successive absorptions of quanta effective in either synthesis or dissociation. Since many collisions follow each synthesis, the difference in pressures, temperatures, and densities between contemporary laboratory and primitive lunar environments should not significantly affect the overall quantum yields.
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From page 11... ...
But it should be emphasized that 85% of the organic material produced in the corona discharge experiments is not amino acids and has not been identified (Miller, 1957)
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From page 12... ...
Such a factor is appropriate only to the times of the early solar nebula before the clearing out of interplanetary space by solar corpuscular radiation (see section II B) , and we neglect it here.
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From page 13... ...
F Lifetime of Secondary Lunar Atmosphere The time for the density of a planetary atmosphere to be reduced to 1/e its initial value by escape to space is determined by the value of Tc, the temperature at the critical level in the atmosphere above which a molecule moving outward with the velocity of escape is unlikely to encounter another molecule.
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From page 14... ...
For this interval, at least, there would have been an appreciable atmosphere. Thus it is not impossible that the relevant lifetime of the secondary lunar atmosphere -- during which organic molecules were produced in the atmosphere and dissolved at the surface -- was as long as 10^ or 108 years.
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From page 15... ...
Organic matter produced in the secondary lunar atmosphere appears to have a much better chance of residing near the present lunar surface and having avoided dissociative processes (cf. section II H below)
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From page 16... ...
As the secondary lunar atmosphere gradually escaped to space, and outgassing declined, the rate of atmospheric organic synthesis decreased and the penetration of short wavelength radiation to the surface increased. In addition, the surface temperature gradually rose, due both to the loss of the insulating atmosphere, and to radioactive heating.
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From page 17... ...
if meteoritic infall causes appreciable mixing of the surface material, then the organic matter should be distributed through the upper lunar surface to a depth not exceeding a few tens of meters. The organic matter should be expected only in regions which have had no extensive lava flows; the southern highland appears to be such a region, as does much of the far side of the Moon.
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From page 18... ...
For more detailed analysis the relative merits and feasibilities of remote gas and paper chromatography, remote spectroscopy, and remote reagent analytic chemistry should be investigated. There is an obvious advantage for the subsurface probing device to be incorporated in a roving lunar surface vehicle; for example, mare and non-mare cores could be compared.
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