The Distribution of Ice in Lunar Permanently Shadowed Regions: Science Enabling Exploration (Invited)

Recent prospecting indicates that water ice occurs in enhanced abundances in some lunar PSRs. That water constitutes a resource that enables lunar exploration if it can be harvested for fuel and life support. Future lunar exploration missions will need detailed information about the distribution of volatiles in lunar permanently shadowed regions (PSRs). In addition, the volatiles also offer key insights into the recent and distant past, as they have trapped volatiles delivered to the moon over ~2 Gyr. This comprises an unparalleled reservoir of past inner solar system volatiles, and future scientific missions are needed to make the measurements that will reveal the composition of those volatiles. These scientific missions will necessarily have to acquire and analyze samples of volatiles from the PSRs. For both exploration and scientific purposes, the precise location of volatiles will need to be known. However, data indicate that ice is distributed heterogeneously on the Moon. It is unlikely that the distribution will be known a priori with enough spatial resolution to guarantee access to volatiles using a single point sample. Some mechanism for laterally or vertically distributed access will increase the likelihood of acquiring a rich sample of volatiles. Trade studies will need to be conducted to anticipate the necessary range and duration of missions to lunar PSRs that will be needed to accomplish the mission objectives. We examine the spatial distribution of volatiles in lunar PSRs reported from data analyses and couple those with models of smaller scale processes. FUV and laser data from PSRs that indicate the average surface distribution is consistent with low abundances on the extreme surface in most PSRs. Neutron and radar data that probe the distribution at depth show heterogeneity at broad spatial resolution. We consider those data in conjunction with the model to understand the full, 3-D nature of the heterogeneity. A Monte Carlo technique simulates the stochastic process of impact gardening on a putative ice deposit. The model uses the crater production function as a basis for generating a random selection of impact craters over time. Impacts are implemented by modifying the topography, volatile content, and depth distribution in the simulation volume on a case by case basis. This technique will never be able to reproduce the exact impact history of a particular area. But by conducting multiple runs with the same initial conditions and a different seed to the random number generator, we are able to calculate the probability of situations occurring. Further, by repeating the simulations with varied initial conditions, we calculate the dependence of the expectation values on the inputs. We present findings regarding the heterogeneity of volatiles in PSRs as a function of age, initial ice thickness, and contributions from steady sources.