Non-Polar Lunar Hydroxyl and Water Using the Moon Mineralogy Mapper

Towards the late stages of differentiation of the early lunar magma ocean, the remaining KREEP layer would have been enriched with thorium, water, hydroxyl, and other incompatible materials. Therefore, locations that show high concentrations of thorium and hydroxyl/water may indicate assimilation of or interaction with KREEP. Using results from the Lunar Prospector Gamma Ray Spectrometer (LP-GRS), we selected thorium anomalies on the Moon in an effort to detect KREEP-rich material using hyperspectral imagery. Four sites were chosen: Lassell Crater (15 S, 8 W), Hansteen Alpha (15 S, 50 W), Gruithuisen Domes (36 N, 40 W), and the Compton-Belkovich Thorium Anomaly (61 N, 100 E). Three of these sites are non-mare volcanic features within the Procellarum KREEP Terrane, while Compton-Belkovich is located on the lunar farside. The Moon Mineralogy Mapper (M3) hyperspectral imager was used to analyze the composition of these locations. The spectra gathered from the volcanic domes all show pronounced absorptions at ~2.8 μm, indicating hydroxyl or water. This is significant for two reasons: (1) the strong absorption of hydroxyl/water shown at each of these volcanic features supports the hypothesis that the lunar mantle is more hydrous than previously thought; and (2) it suggests that KREEP may lie, possibly as uncoupled pods, beneath the anorthositic highlands near Compton-Belkovich as well as beneath other areas outside the previously defined Procellarum KREEP Terrane.