The Distribution of Molecular Water in the Lunar South Polar Region based upon 6-micron Spectroscopic Imaging

TL;DR

This study uses infrared spectroscopic imaging from SOFIA to map molecular water distribution across the lunar south polar region, revealing spatial variability and localized water enhancements related to topography and shadowed areas.

Contribution

First detailed 6-micron spectroscopic imaging of lunar water distribution, highlighting regional and local variations linked to surface features and shadowed regions.

Findings

Water content varies from dry to ~170 ppm across the region.

Localized water enhancements are associated with high-altitude and shadowed features.

Water distribution decreases toward the lunar pole.

Abstract

The amount and distribution of water on the lunar surface are related to the input and production of water by solar wind and meteoroid bombardment, balanced by photodestruction and mobility across the surface. Using the Stratospheric Observatory for Infrared Astronomy (SOFIA), we imaged the 6.1 micron feature that uniquely traces molecular water, covering 1/4 of the lunar nearside surface south of -60 degrees latitude with 5 km resolution on 2022 Feb 17 UTC. The water feature strength varies significantly across the region, being drier at +28 degrees longitude to more wet (~170 ppm) at -7 degrees longitude, and also decreasing toward the pole. Significant local enhancements are found, associated with south-facing, high-altitude topographic features. This includes relatively high H2O concentration in a "wet ridge" just north of Curtius crater; the south-facing, northern, inner rims of most prominent craters; the south face of the central peak of Moretus crater; and permanently-shadowed polar regions.