Molecular Water at High Southern Latitudes on the Moon

The water molecule is a key compound for understanding the interaction of airless planetary surfaces with the space environment. In the contemporary era, water molecules have two principal styles of emplacement in the space weathering process: 1) they can be directly introduced into the lunar environment via micrometeorite impacts or 2) synthesized from solar wind hydrogen. While characterizing the behavior and origin of water is important to understanding the planetary process that is space weathering, it is of topical importance owing to the value of water for the progress of space exploration.

In this presentation we describe measurements of lunar surface water by Stratospheric Observatory for Infrared Astronomy (SOFIA) that confirm the presence of molecular water in the south pole region near Moretus crater. We present a map of water emission in this region that enables tests of various hypotheses for water formation and variation. Mean water abundances detected are about 250 μg/g over that of a mare reference surface at Mare Fecunditatis. We find that water abundances are locally anticorrelated with temperature. The distribution of water is consistent with derivation of water from pre-existing hydroxyl subsequently trapped in impact glass, provided hydroxyl increases with latitude as some models and measurements suggest. The detected water cannot be in equilibrium with the exosphere because insufficient water is present in the exosphere to maintain the surface abundance. The data are consistent with a high latitude water-bearing mineral host that may be a precursor to recently detected high latitude hematite.