Mapping the 6 Micron Molecular Water Line Across the Lunar Surface (Pilot Legacy Program)
PI: Paul Lucey (University of Hawaii at Manoa)
The Cycle 9 Legacy proposal 09_0171 is approved as a pilot but will be executed in Cycle 8 using Director’s Discretionary Time.
Proposal ID: 09_0171
Instrument: FORCAST

Abstract Excerpt: SOFIA+FORCAST made an unprecedented detection of molecular water (H2O) on the lunar surface that raised new questions surrounding the behavior, formation, and storage of water on the Moon. Prior to this detection, it was suggested that water existed on the sunlit Moon and may be responsible for the variations observed in the 3 µm hydration band and UV water ice band ratio. However, it is unknown if the variations are caused by water or its close cousin hydroxyl (OH), which can spectrally mimic H2O at 3 µm. Spectroscopy at 3 µm and in the UV currently do not distinguish between water and hydroxyl. New methods were needed to uniquely detect H2O on the Moon. H2O features a fundamental bending mode at 6 µm that is strictly due to H2O without confusion from OH. However, the 6 µm spectral region is inaccessible from the ground, and measurements at 6 µm are lacking in existing or planned lunar spacecraft. The unique capabilities provided by SOFIA+FORCAST enabled the first detection of H2O on the sunlit Moon. At SOFIA’s operational altitude, the low telluric atmospheric water vapor allows for observations of the Moon at 6 µm. Data obtained during a test flight in 2018 showed a strong 6 µm emission feature at high southern latitudes. This Legacy project will address fundamental questions raised by the detection of H2O on the sunlit Moon and produce maps of water across the Moon at multiple lunar times of day and of geologically important locations that may indicate the presence of interior water. The maps will inform us about the migration and storage of water and may be used to determine locations with high potential for resource extraction during the NASA Artemis and VIPER programs. The characterization of water on the Moon will be applicable to the understanding of water on other airless bodies in the Solar System and exoplanets.