A map of surface molecular water was derived from long slit spectroscopy of the south polar region of the Moon using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) spectrometer on the Stratospheric Observatory for Infrared Astronomy (SOFIA). Mean water abundances detected are about 250 µg/g over that of a mare reference surface at Mare Fecunditatis. Water abundances are locally anticorrelated with temperature and latitude. 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 to maintain the surface abundance. The data are also consistent with a high latitude water-bearing mineral host that may be a precursor to recently detected high latitude hematite.

Prior to 2009, the Moon was believed to be anhydrous. However, observations by three spacecraft revealed a hydrated surface by reporting a 3 µm absorption band attributed to hydroxyl and possibly molecular water. The Moon Mineralogy Mapper (M) spectrometer, onboard the Chandrayaan-1 spacecraft is mainly used to study the lunar 3 µm band but its spectral range ends at 3 µm. The limited wavelength range of Mhas allowed observed variations in the 3 µm band to be called into question due to uncertainties in thermal corrections. To investigate the validity of variations in the lunar 3 µm band, we used the SpeX infrared spectrograph at the NASA InfraRed Telescope Facility at Maunakea Observatory in Hawaiʻi. With SpeX, we are able to obtain lunar data over a wavelength range of 1.67 to 4.2 µm at 1 – 2 km spatial resolution. The long wavelengths provide strong constraints on thermal emission corrections. We confirm that the 3 µm band varies with lunar time of day as well as with latitude and composition. Each observation reveals strong variations in abundances of hydroxyl and possibly molecular water. The data reveal a decrease in abundance with increasing lunar local time, an asymmetric trend about the equator that favors the southern latitudes, and higher concentrations in highland regions. The longer wavelengths provided by SpeX have allowed us to examine variations in the 3 µm band and provide definitive evidence that the variations are due to changes in hydration.