Earthshine at the Lunar Poles and Volatile Stability

Introduction: In the context of resumed lunar exploration , the existence of water ice at the lunar poles has become a pressing question. In support of human return to the moon, the confirmation of the water ice signature detected from orbiting spacecraft [1,2] is a high-priority task that can only be accomplished in situ. Therefore, a landed mission to the permanently shadowed lunar polar craters is required. It has been assumed that the landing site for ice validation would be permanently shadowed from the Earth as well as the sun, implying physical conditions with which the landed spacecraft would have to contend, prominently the absence of direct line-of-sight (LOS) to Earth communications. Mission architecture and cost is highly dependent on whether a telecommunications relay satellite is required. If there are likely deposits of near-surface water ice in locations permanently shadowed from the sun yet having direct LOS to the earth, then the mission is much less complex (no detailed planning of observations and transmissions to meet the orbital constraints imposed by the relay satellite) and much less expensive (~$100 M for designing, building, and additional launch and operations cost for the relay). Therefore, it would be advantageous to conduct the ice validation mission at a site illuminated by the Earth. Radar maps from Arecibo [3] have demonstrated that the lunar Polar Regions are periodically visible from earth in accordance with the lunar cycle. Furthermore , it has been shown that radar coverage of the lunar South Pole overlaps with a few, small areas of permanent , lunar summer shadow [4]. Therefore, a simple, precision guided mission to an appropriate site at the lunar South Pole should be able to conduct the ice validation mission [5]. It has been claimed however, that earthshine provides sufficient incident flux to evaporate the putative ice deposits and that therefore, lunar ice finder missions will need to access sites invisible from earth and hence require r elay assets. Hence, this work will calculate the incident radiative flux from the earth and estimate the implied lunar surface temperature, thus evaluating the stability of lunar ice deposits subject to terrestrial irradiance. Fluxes and Surface Temperature: In order to determine whether earthshine will evaporate the putative lunar ice deposits one must calculate the radiative flux from the earth. To simplify the calculation it was assumed that the earth is fixed at an elevation 10 degrees or less above …