The possible hydrogen anomalies in KREEP terrain according to the results of LEND and LPNS data

Abstract

Distribution of epithermal neutron flux and hydrogen content from equatorial surface of the Moon, obtained by neutron spectrometers LEND and LPNS is studied. The positions of spots with reduced neutron flux, so-called NSRs (Neutron Suppression Regions), in the KREEP terrain are determined. We found that typical decreasing of epithermal neutron flux is about δ=1–7% for NSRs around the equatorial lunar surface relative the comparison zone associated with crater Tycho. Mean value of neutron flux suppression for KREEP region is nearly δ=4.6%. This value corresponds to the average concentration of hydrogen CH=62ppm included in any hydrogen compounds, incorporated in the regolith layer with depth up to 1m. For all equatorial regions of the Moon (70°S–70°N latitude) the average suppression factor δ=3% corresponds to mean value of hydrogen content nearly 55ppm. It has been recognized strong correlations between NSRs in KREEP with volcanic and impact formations, related to Mare Imbrium. The largest of the considered NSRs are located in Fra-Mauro crater (δ=7.2%, CH=127.5ppm) and in Iridium terrain area (δ=6.9%, CH=82.2ppm). These two hydrogen anomalies undoubtedly are related to the impact processes formed Mare Imbrium. Possible origins of epithermal neutron suppressions in KREEP, concerning both implanted solar wind protons and indigenous lunar hydrogen are discussed.