¹David J. Lawrence, ¹Patrick N. Peplowski, ¹Jeffrey B. Plescia, ²Benjamin T. Greenhagen, ³Sylvestre Maurice, ⁴Thomas H. Prettyman
¹The Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Institut de Recherche en Astrophysique et Planétologie, Toulouse, France
⁴Planetary Science Institute, Tucson, Arizona, USA

A map of bulk hydrogen concentrations in the lunar highlands region is reported. This map is derived using data from the Lunar Prospector Neutron Spectrometer (LP-NS). We resolve prior ambiguities in the interpretation of LP-NS data with respect to non-polar hydrogen concentrations by comparing the LP-NS data with maps of the 750 nanometer albedo reflectance, optical maturity, and the wavelength position of the thermal infrared Christiansen Feature. The best explanation for the variations of LP-NS epithermal neutron data in the lunar highlands is variable amounts of solar-wind-implanted hydrogen. The average hydrogen concentration across the lunar highlands and away from the lunar poles is 65 ppm. The highest hydrogen values range from 120 ppm to just over 150 ppm. These values are consistent with the range of hydrogen concentrations from soils and regolith breccias at the Apollo 16 highlands landing site. Based on a moderate-to-strong correlation of epithermal neutrons and orbit-based measures of surface maturity, the map of highlands hydrogen concentration represents a new global maturity index that can be used for studies of the lunar soil maturation process. We interpret these hydrogen concentrations to represent a bulk soil property related to the long-term impact of the space environment on the lunar surface. Consequently, the derived hydrogen concentrations are not likely related to the surficial enhancements (top tens to hundreds of microns) or local time variations of OH/H2O measured with spectral reflectance data.

Reference
Lawrence DJ, Peplowskia, Plescia JB, Greenhagen BT, Maurice S, Prettyman TH (2015) Bulk Hydrogen Abundances in the Lunar Highlands: Measurements from Orbital Neutron Data. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.005]

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