Lunar Outgassing, Transient Phenomena and The Return to The Moon, I: Existing Data

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. This subset is highly correlated geographically with the catalog of outgassing events seen by the Apollo 15, 16 and Lunar Prospector alpha-particle spectrometers for episodic Rn gas release. 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, a long-lived product of Rn decay and a further tracer of outgassing. This offers a second 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 (while moonquakes are not), which may indicate the effects of cracks caused by the impacts, or perhaps avalanches, allowing release of gas. The majority of TLP (and Rn) activity, however, is confined to one area likely to have been a major volcanic effusion site, and plausibly might connect with the deep lunar interior. In an accompanying paper we discuss likely theoretical implications of past and present outgassing and its connection to TLPs. We also present methodologies for remote and in-situ observations of TLPs and manifestations of lunar outgassing. These include several ground-based methods which can be implemented immediately. With the coming exploration in the next few years by a fleet of robotic spacecraft, followed by human exploration, the study of TLPs and outgassing is both promising and imperiled. We will have an unprecedented opportunity to study lunar outgassing, but will also deal with a greater burden of anthropogenic lunar