Hydrogen Mapping of the Lunar South Pole Using the LRO Neutron Detector Experiment LEND

Abstract

Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon's south polar region from the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) spacecraft were used to select the optimal impact site for LCROSS. LEND data show several regions where the epithermal neutron flux from the surface is suppressed, which is indicative of enhanced hydrogen content. These regions are not spatially coincident with permanently shadowed regions of the Moon. The LCROSS impact site inside the Cabeus crater demonstrates the highest hydrogen concentration in the lunar south polar region, corresponding to an estimated content of 0.5 to 4.0% water ice by weight, depending on the thickness of any overlying dry regolith layer. The distribution of hydrogen across the region is consistent with buried water ice from cometary impacts, hydrogen implantation from the solar wind, and/or other as yet unknown sources.

Surface Composition of Vesta: Issues and Integrated Approach

“…Measurements by Lunar Prospector's neutron spectrometer revealed excess hydrogen in lunar polar areas where there are permanently shadowed regions; however, the chemical form of H could not be determined from measurements of neutrons (Feldman et al 1998(Feldman et al , 2000(Feldman et al , 2001Lawrence et al 2006;Eke et al 2009). Excess hydrogen at the poles was also detected by the Lunar Reconnaissance Orbiter (LRO) mission's Lunar Explorer Neutron Detector (LEND) (Mitrofanov et al 2010a(Mitrofanov et al , 2010b(Mitrofanov et al , 2010cLawrence et al 2010), confirming the earlier findings. The Moon Mineralogy Mapper (M 3 ) imaging spectrometer on Chandrayaan-1 recently reported the widespread occurrence of reflectance spectrum absorptions in the 3-µm spectral region that appear the same as is commonly seen for OH and H 2 O-rich surfaces in the laboratory and other parts of the solar system ).…”

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

“…Other evidence includes data from a set of IR sensors showing an OH veneer that extends all the way down to the lunar equator, and which may even possess a present-day, dynamic diurnal component (Pieters et al 2009;Clarke et al 2009;). The distribution of water in the lunar polar regions is heterogeneous on all observed scales (Mitrofanov et al 2010).…”

Technical Comment on “Hydrogen Mapping of the Lunar South Pole Using the LRO Neutron Detector Experiment LEND”

“…T he paper by Mitrofanov et al (1) provides new interpretations about the distribution of lunar polar hydrogen (H) abundances using data from the Lunar Exploration Neutron Detector (LEND) on NASA's Lunar Reconnaissance Orbiter (LRO). Based on the presence of a significant uncollimated background from high-energy epithermal (HEE) neutrons and consistent observations of the global neutron emission as measured using the neutron spectrometers on Lunar Prospector (LP) and LRO missions, we conclude that claims of enhanced H abundance in sunlit portions of the lunar south pole and quantitative H concentration values in south pole permanently shaded regions (PSR) are insufficiently supported.…”