On the Effect of Magnetospheric Shielding on the Lunar Hydrogen Cycle

TL;DR

This study models how Earth's magnetotail influences lunar water production by affecting solar wind proton flux, showing that shielding during the Moon's passage through the magnetotail impacts hydrogen-related water formation.

Contribution

It introduces a new model linking Earth's magnetospheric shielding to lunar hydrogen cycle variations, aligning well with observational data.

Findings

Water production varies with lunar position relative to Earth's magnetotail.

Shielding reduces hydrogen influx and water formation during full Moon.

Model results agree with observational measurements.

Abstract

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.