Permanently shadowed regions (PSRs) at the lunar poles pique scientific interest on account of their cold trapping of volatiles that is highly relevant in the current scope of lunar exploration. Interiors of PSRs are largely unknown due to the challenging illumination conditions. In this letter, we describe a method for synthesizing images at PSRs based on the knowledge of incident solar illumination geometry and local topography that reflects light into PSRs.

Water ice and other volatile compounds may be present on the Moon's surface within permanently shadowed regions (PSRs) near the lunar poles. Understanding the composition, quantity, distribution, and form of water and other volatiles associated with lunar PSRs is identified as a Strategic Knowledge Gap (SKG) for NASA's human exploration program, projected to visit the lunar south pole in the next decade. These polar volatile deposits are also scientifically interesting, having potential to reveal important information about the delivery of water to the Earth-Moon system.

We follow Paper I with predictions of how gas leaking through the lunar surface could influence the regolith, as might be observed via optical transient lunar phenomena (TLPs) and related effects. We touch on several processes, but concentrate on low and high flow rate extremes, which are perhaps the most likely. We model explosive outgassing for the smallest gas overpressure at the regolith base that releases the regolith plug above it. This disturbance's timescale and affected area are consistent with observed TLPs; we also discuss other effects. For slow flow, escape through the regolith is prolonged by low diffusivity. Water, found recently in deep magma samples, is unique among candidate volatiles, capable of freezing between the regolith base and surface, especially near the lunar poles. For major outgassing sites, we consider the possible accumulation of water ice. Over geological time, ice accumulation can evolve downward through the regolith. Depending on gases additional to water, regolith diffusivity might be suppressed chemically, blocking seepage and forcing the ice zone to expand to larger areas, up to km(2) scales, again, particularly at high latitudes. We propose an empirical path forward, wherein current and forthcoming technologies provide controlled, sensitive probes of outgassing. The optical transient/outgassing connection, addressed via Earth-based remote sensing, suggests imaging and/or spectroscopy, but aspects of lunar outgassing might be more covert, as indicated above. TLPs betray some outgassing, but does outgassing necessarily produce TLPs? We also suggest more intrusive techniques from radar to in situ probes. Understanding lunar volatiles seems promising in terms of resource exploitation for human exploration of the Moon and beyond, and offers interesting scientific goals in its own right. Many of these approaches should be practiced in a pristine lunar atmosphere, before significant confusing signals likely to be produced upon humans returning to the Moon.

Transient lunar phenomena (TLPs) have been reported for centuries, but their nature is largely unsettled and remains controversial. In this Paper I the database of TLP reports is subjected to a discriminating statistical filter robust against sites of spurious reports, and produces a restricted sample that may be largely reliable, and is highly correlated geographically with event catalogs from Apollo and Lunar Prospector alpha-particle spectrometers for episodic Rn-222 gas releases. Both this robust TLP sample and even the larger, unfiltered sample are highly correlated with the boundary between mare and highlands, as are both deep and shallow moonquakes, as well as Po-210, a long-lived product of Rn-222 decay and another tracer of outgassing. This offers another significant correlation relating TLPs and outgassing, and may tie some of this activity to sagging mare basalt plains (perhaps mascons). Additionally, low-level but likely significant TLP activity is connected to recent, major impact craters (hile moonquakes are not), which may indicate the effects of impact fracturing, or perhaps avalanches, allowing release of gas. Most TLP (and Rn-222) activity, however, is confined to one area likely causing major, recent volcanic effusion, and plausibly connected to the deep lunar interior. Our accompanying paper (rotts & Hummels) treats likely theoretical implications, plus practical methodologies for remote and in situ TLP and lunar outgassing observations. With the coming fleet of robotic lunar spacecraft, followed by human exploration, the study of TLPs and outgassing is both promising and imperiled. We anticipate a greater burden of anthropogenic lunar gas than ever produced, perhaps outstripping the natural atmosphere itself, but also unprecedented opportunities to study lunar outgassing and its sources if these can be examined promptly, in their pristine state.