An Indirect Search for Lunar Polar Ices FRANCIS G. GRAHAM Summary The possibility of comet-derived ices in permanently shadowed lunar polar craters has been a question for space development for years. Calculations have shown that loss mechanisms exceed present flux; larger primordial cometary input would also now be gone. However, Nemesis theory bombardment scenarios, which are postulated to have caused mass extinctions on Earth, would also have caused episodic cometary impacts on the moon, as recently as 13 million years ago, probably sufficient for the maintenance of lunar polar ices by the Arnold mechanism. Less volatile cometary compounds, such as sodium compounds, might have also survived in partially shadowed lunar polar areas where the sun is always low and partially hidden by terrain. Observational experiments were conducted to detect any enhanced sodium vapor emission at the lunar poles. These results were negative at the expected levels. If cometary materials less volatile than ices are not detected at the partially shadowed lunar areas, then doubt exists for the ices’ existence in the permanently shadowed craters. Introduction A large supply of water ice present on the Moon would be a valuable resource to lunar settlement economies [1,2]. Hydrogen is one of the most deficient elements of the lunar surface, and is necessary for human life and many activities in manufacturing. In the literature, outlined below, there is the hope expressed that such ices may be found in permanently shadowed lunar craters. Because of the Moon’s low obliquity (1.5°), portions of deep craters at the lunar poles are permanently in shadow. In the lunar north polar regions, craters include the northern part of Sylvester and the northwest part of Peary, as well as other craters near Peary surrounding the north pole. The lunar south polar region has not yet received adequate mapping to surely permit crater identification, although recently the control grid was extended to new features in preparation for a final map [3-5], Due to the low thermal conductivity of rock, ices inside these polar craters derived from comets and other sources presumably would remain frozen for a considerable time. Watson et al. [6] originated this concept, but the model for deposition of cometary ices was developed in its fullest form by Arnold [7]. The Arnold model begins with the impact of a comet or a degraded cometary nucleus (Arnold, citing others, suggests Apollo asteroids are degraded comentary nuclei; other asteroid classes also contain hydrated minerals which might in addition serve as sources of ice). The Francis G. Graham, Kent State University, Physics, 400 East 4th Avenue, East Liverpool, OH 43920, USA.
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