The Lunar Poles: Water Ice or Chemically Trapped Hydrogen?

An alternative explanation is proposed for the hydrogen excess observed by the Lunar Prospector neutron spectrometer: solar wind protons trapped on radiation defects in regolith particles and effectively retained at the temperature of the lunar poles can be misinterpreted as water. Protons from the Earth's magnetotail plasma can be a source of hydrogen atoms in the regolith of permanently shadowed areas of the lunar surface.