Lunar Outgassing, Transient Phenomena and The Return to The Moon, II: Predictions for Interactions between Outgassing and Regolith

TL;DR

This paper explores how lunar outgassing interacts with regolith and potentially causes optical Transient Lunar Phenomena (TLPs), considering both explosive and slow gas flow scenarios, and discusses implications for surface appearance and ice formation.

Contribution

It provides a detailed analysis of gas-regolith interactions at different flow rates and predicts how these processes could produce observable TLPs and influence lunar surface features.

Findings

Explosive gas release can displace regolith, causing TLP-like phenomena.

Water vapor can freeze and form ice layers within the regolith.

Slow gas seepage may lead to extensive ice accumulation and surface changes.

Abstract

We consider the implications from Paper I on how gas leaking through the lunar surface might interact with the regolith, and in what respects this might affect or cause the appearance of optical Transient Lunar Phenomena (TLPs). We consider briefly a range of phenomena, but concentrate at the extremes of high and low gas flow rate, which might represent the more likely behaviors. Extremely fast i.e., explosive, expulsion of gas from the surface is investigated by examining the minimal amount of gas needed to displace a plug of regolith above a site of gaseous overpressure at the regolith's base. The area and timescale of this disturbance, it is consistent with observed TLPs. Furthermore there are several ways in which such an explosion might be expected to change the lunar surface appearance in a way consistent with many TLPs, including production of obscuration, brightening and color changes. At the slow end of the volatile flow range, gas seeping from the interior is retained below the surface for extensive times due to the low diffusivity of regolith material. A special circumstance arises if the volatile flow contains water vapor, because water is uniquely capable of freezing as it passes from the base to the surface of the regolith. For a large TLP site, it is plausible to think of areas on the square-km scale accumulating significant bodies of water ice. Furthermore, as the system evolves over geological time, the ice accumulation zone will evolve downwards into the regolith. Since many reactions possible between the volatiles and regolith, depending on the additional gases besides water, can act to decrease diffusivity in the regolith, it is plausible that the volatiles produce a barrier between the seepage source and vacuum, forcing the ice zone to expand to larger areas.