Landing At Ice Exposures In The Lunar Polar Regions

Shuai Li
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Landing At Ice Exposures In The Lunar Polar Regions
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We recently discovered water ice absorption features centered near 1.3, 1.5, and 2.0 m in M3 data within permanently shadowed regions (PSRs) near the lunar poles. These locations also show low temperatures (annual maximum temperature less than 110K), enhanced LOLA albedo, and high ‘off’ and ‘on’ band ratios of LAMP data, supporting the presence of surface exposed water ice, which has important implications for future in situ resource utilization on the Moon. However, our results suggest that only around 3.5% of the PSRs which have annual maximum temperatures low enough (110 K) to preserve ice for geologic time against sublimation. This is distinct from Mercury and Ceres where ice was found at almost all PSRs. In addition, deposits of nearly pure water ice were inferred for cold traps on Mercury and Ceres, whereas the lunar surface exposed ice showed much lower abundance (~30 wt. %). The delivery, transport, and/or retention of volatiles at the optical surface of the Moon is distinct from other inner solar system objects that have similar cold traps at their poles [Li et al., 2017]. We propose these ice exposures as landing sites for future lunar missions to understand the physical processes responsible for these differences and the time scales on which they operate, and to assess the possibility of utilizing these ice deposits as in situ resources. We examined the local geomorphology of ice exposures using the LRO long-exposure NAC images of PSRs where ice exposures were clustered. No significant enhancement in albedo was observed, which is in accordance with the low ice abundance estimated from M3 data. To evaluate whether a location is appropriate for landing, we examined the 30m DEM data derived from the LOLA and Kaguya terrain camera at all ice exposure sites. The craters Haworth, Shoemaker, Faustini, and Sverdrup are candidates for landing near the south pole, while the crater interiors of Rozhdestvenskiy U and Hermit A, and the southern walls of Hermit and Rozhdestvenskiy would be candidates in the north pole. These proposed locations show relatively smooth areas greater than 100 km2, but we can optimize the locations to ranges within few km2 if necessary. Mobility is necessary because the ice exposures are patchy. Since few PSRs showed ice absorption features in M3 data, we examined the intensity of scattered light at all PSRs and found that the ice exposures are associated with the weakest scattered light. However, not all PSRs receiving weak scattered light have ice exposures. The most noticeable PSRs of such type are Amundsen, Hedervari, and Wiechert that may have located at lower latitudes and thus been warmer or not permanently shaded before the Moon’s axis shifted to the current location [Siegler et al., 2016]. Alternatively, the absence of ice features could be related to a lack of high quality of M3 data. Measuring the age of these ice deposits will help to test our hypothesis. Since the lunar polar wander was hypothesized to occur at around 3 Ga ago, those observed ice might be even older. The accumulation of ice on the Moon after relocating to its current poles might be extremely slow. Future missions can also help measure the depth of these ice deposits to assess the possibility of utilizing the ice as in situ resources. If dating the ice age can be done in situ, no sample return is needed. [1] Li, S., P. G. Lucey, and R. E. Milliken (2017), Evidence of the surface exposed water ice in the lunar polar regions seen by the Moon Mineralogy Mapper, SSERVI. [2] Siegler, M., R. Miller, J. Keane, M. Laneuville, D. Paige, I. Matsuyama, D. Lawrence, A. Crotts, and M. Poston (2016), Lunar true polar wander inferred from polar hydrogen, Nature, 531(7595), 480-484.
Paul Lucey, and Erwan Mazarico