  We examine how water is produced globally over the lunar surface as it orbits
in/out of the magnetotail. Due to the interaction of the solar wind (SW) with
Earth's magnetic field, upstream the magnetic field is compressed down to ~10
Earth radii. However, the diverted stream of SW around Earth's magnetic field
results in an extended depleted region of SW protons (positively charged
hydrogen) out to 1000's of Earth radii, referred to as the magnetotail. The
Moon orbits at a distance of ~40 Earth radii; therefore, upstream it is within
the SW, but downstream it is partially shielded while in the magnetotail during
full Moon. SW protons penetrate lunar soil particles and some H atoms can
chemical react with oxygen to form water-like molecules such as OH/H2O. Most of
the H atoms bounce around within grains until finding another hydrogen atom,
chemically combine, and then escape the grain as H2 into the thin atmosphere.
We developed a model to calculate the global distribution of OH produced in the
lunar surface and H2 released to the atmosphere as the Moon orbits in/out of
Earth's magnetotail. The model results are in good agreement with available
observations.
