Electrons Creating Water on Moon?

A team of researchers discovered that high energy electrons in Earth's plasma sheet are contributing to weathering processes on the Moon's surface and that the electrons may have aided in the formation of water on the lunar surface.

The findings were published in the journal Nature Astronomy.

Understanding water concentrations and distributions on the Moon is critical for understanding its formation and evolution, as well as providing water resources for future human exploration.

The new discovery may also help explain the origin of the previously discovered water ice in the permanently shaded regions of the Moon.

Because of Earth's magnetism, a force field known as the magnetosphere surrounds the planet, protecting it from space weathering and damaging radiation from the Sun. The magnetosphere is pushed and reshaped by the solar wind, resulting in a long tail on the night side.

The plasma sheet within this magnetotail is a region made up of high-energy electrons and ions that could come from Earth or the solar wind.

Previously, scientists concentrated on the role of high-energy ions in the weathering of the Moon and other airless bodies in space. The solar wind, which is made up of high-energy particles like protons, bombards the lunar surface and is thought to be one of the primary ways water forms on the Moon.

Shuai Li, the assistant researcher at the UH Manoa School of Ocean and Earth Science and Technology (SOEST), was interested in investigating the changes in surface weathering as the Moon passes through Earth's magnetotail, an area that almost completely shields the Moon from the solar wind but not the Sun's light photons, based on his previous work that showed oxygen in Earth's magnetotail is rusting iron in the Moon's polar regions.

“This provides a natural laboratory for studying the formation processes of lunar surface water,” said Li.

“When the Moon is outside of the magnetotail, the lunar surface is bombarded with solar wind. Inside he magnetotail, there are almost no solar wind protons and water formation was expected to drop to nearly zero.”

Li and colleagues examined remote sensing data collected by India's Chandrayaan 1 mission's Moon Mineralogy Mapper instrument between 2008 and 2009. They looked at how water formation changed as the Moon passed through Earth's magnetotail, which includes the plasma sheet.

“To my surprise, the remote sensing observations showed that the water formation in Earth’s magnetotail is almost identical to the time when the Moon was outside of the Earth’s magnetotail,” said Li.

“This indicates that, in the magnetotail, there may be additional formation processes or new sources of water not directly associated with the implantation of solar wind protons. In particular, radiation by high energy electrons exhibits similar effects as the solar wind protons.”

“Altogether, this finding and my previous findings of rusty lunar poles indicate that Mother Earth is strongly tied with its Moon in many unrecognized aspects,” said Li.