Volcanic Outgassing from Lunar Maria as a Possible Source of Polar Volatiles: 3-D Simulation of Volatile Transport by Transient Volcanically-Induced Atmospheres.

Abstract:

Since the discovery of lunar polar volatiles in 1990s their origin and distribution remain an open question. This becomes even more pressing with the prospect of a human outpost on the Moon in the near future. Typically, three sources of volatiles are considered: solar wind, volatile-rich impactors, and volcanic outgassing from the planetary interior. In this work we concentrate on volcanic outgassing from lunar maria during the peak of the Moon’s volcanic activity ~3.5 Ga.

Major eruptions are capable of releasing sufficient volatiles to produce a transient tenuous atmosphere. If a repose time between the eruptions is sufficiently short (so that the atmosphere doesn’t completely escape to space in the meantime), then the atmosphere can accumulate to sufficiently thick pressures (up to 1000 Pa according to [1]), though recent research [2] shows that the probability of such scenario is rather low, and the era of a volcanically active Moon was likely to have been dominated by very thin (0.025 – 0.25 Pa [2]) short lived (a few thousand years) single-eruption atmospheres. Although very thin, such atmospheres would still be collisional and would play an important role in volatile transport. In this respect they would be similar to a transient lunar atmosphere produced by a cometary impact, which was shown to play an important role in transporting of cometary water to the cold traps [3].

Here we investigate the fate of water released by a typical major volcanic eruption, and the ability of tenuous volcanically-induced atmospheres to transport such water to the poles. In this work we assume that volatiles from previous eruptions do not disappear completely, but provide a thin background atmosphere, though we expect our results to scale well in a limit of very thin atmospheres. For our simulations we use ROCKE-3D [4] planetary climate model. We investigate the efficiency of volatile transport for a wide parameter space typical for the Moon 3.5 Ga such as the Moon’s obliquity, and thickness and composition of the background atmosphere. Our results show that in most cases the volatiles are efficiently transported to the poles.

[1] Needham D. H. and Kring D. A. (2017) Earth Planet. Sci. Lett., 478, 175.

[2] Wilson L. et al. (2019) LPSC 50, abs. 1343.

[3] Prem P. et al. (2015), Icarus, 255, 148.

[4] Way M. J. et al. (2017) ApJS, 231, 12.