Remote detection of widespread indigenous water in lunar pyroclastic deposits

Laboratory analyses of lunar samples provide a direct means to identify indigenous volatiles and have been used to argue for the presence of Earth-like water content in the lunar interior. Some volatile elements, however, have been interpreted as evidence for a bulk lunar mantle that is dry. Here we demonstrate that, for a number of lunar pyroclastic deposits, near-infrared reflectance spectra acquired by the Moon Mineralogy Mapper instrument onboard the Chandrayaan-1 orbiter exhibit absorptions consistent with enhanced OHand/or H2O-bearing materials. These enhancements suggest a widespread occurrence of water in pyroclastic materials sourced from the deep lunar interior, and thus an indigenous origin. Water abundances of up to 150 ppm are estimated for large pyroclastic deposits, with localized values of about 300 to 400 ppm at potential vent areas. Enhanced water content associated with lunar pyroclastic deposits and the large areal extent, widespread distribution and variable chemistry of these deposits on the lunar surface are consistent with significant water in the bulk lunar mantle. We therefore suggest that water-bearing volcanic glasses from Apollo landing sites are not anomalous, and volatile loss during pyroclastic eruptions may represent a significant pathway for the transport of water to the lunar surface.