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Synthesis of Current Data on Helium and Hydrogen Concentrations in Lunar Regolith


Combined results of (1) analysis and subsequent interpretation of Apollo regolith and regolith breccia samples, (2) mapping of Hydrogen concentrations in the upper regolith by neutron spectroscopy by Lunar Prospector, (3) the LRO LCROSS impact into permanently shadowed regolith at the lunar south pole, and (4) Earth-based spectroscopic and LRO analysis of the lunar transient atmosphere lead to the following tentative conclusions:

  1. 1.Exposed to steady state deposition and release, ilmenite-rich regolith preferentially retains solar wind-derived Helium versus ilmenite-poor regolith.
  2. 2.Water and other volatile compounds and elements have been trapped in permanently shadowed areas at high latitudes.
  3. 3.Exposed to the steady state deposition and release, plagioclase-rich regolith preferentially retains solar wind-derived Hydrogen versus plagioclase-poor regolith.
  4. 4.Sodium in the lunar transient atmosphere suggests that solar wind protons displace mono-valent Sodium (and possibly Potassium) present in solid solution in the crystal lattice of plagioclase. Similar cation replacement takes place during weathering of plagioclase on Earth.
  5. 5.Cold trapping of Helium-3 in high latitude regions may occur, however, direct measurement of its degree is not currently feasible.
  6. 6.Helium in the lunar transient atmosphere indicates that thermal and/or micro-meteor impact releases solar wind volatiles from the regolith, making those volatiles subject to migration and re-implantation as well as entrainment in the passing solar wind.
  7. 7.No data exists on the concentration of solar wind-derived Hydrogen or Helium in permanently shadowed areas. The density of transient Helium in the lunar atmosphere, however, shows little or no latitudinal variation in surface derivation.

Available information points future commercial lunar Helium-3 production toward the “inferred resource” areas in Mare Tranquillitatis. The potential remains great, however, for the existence of commercial quantities of cold-trapped Helium-3 in the regolith of high latitude plains. This potential is significant enough that any Helium-3 production initiative should seriously evaluate the cost and benefit of a lunar orbiter mission capable of mapping Helium-3 distribution at high latitude as well as globally.