THICKNESSES OF VOLCANICALLY-DERIVED WATER DEPOSITS AT THE LUNAR POLES (Invited Presentation)

Lunar polar regions preserve hydrogen-bearing materials (e.g., [1-6]), but the lateral and vertical distributions of these materials remain unclear. Volatile distribution depends on the age and mechanism of delivery to the Moon, how they migrate to the lunar poles, mode of deposition, and subsequent geologic processes. Sources for H-bearing materials are solar wind [7], asteroids/comets [8], ancient volcanic eruptions [9], and leaking from the lunar crust [10]. Volatiles released during lunar volcanic activity may account for all currently observed polar hydrogen if only 0.1% of those volatiles migrated to the lunar poles [9]. This work aims to gain insight into the vertical distribution of lunar polar volatiles by calculating the deposit thicknesses expected for volcanically derived H2O upon initial delivery to the lunar polar regions ~3.5 Ga.

To estimate the initial thickness of H₂O, we take the mass of volcanically derived volatiles [9], convert to volume, and divide by areas where water is expected to be stable to depths of ~2.5 m [11]. Our calculations indicate that, at the Moon’s current orientation, water released during volcanic activity ~3.5 Ga would have formed a layer ~1.5 m thick in regions of expected ice stability. Regardless of origin, water deposits would have been subjected to removal and burial by subsequent impacts and mixing during regolith formation, possibly resulting in a thinner deposit in the shallow substrate [12] or in diffuse mixtures of H-bearing volatiles and regolith [13]. An exploratory surface mission to these regions would verify volatile depth, composition, and concentration.

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