High-energy electrons located in a plasma tail around the Earth are damaging the Moon and, even more interestingly, appear to have given rise to water on the lunar surface.
The new findings, achieved by a team of researchers led by Shuai Li, a scientist at the University of Hawaii at Mānoa School of Ocean and Earth Science and Technology, could also explain how water collects in pockets on the Moon that they never see sunlight called permanently shaded regions (PSR).
Knowledge of the distribution and concentration of water on the Moon is not only essential for understanding how Earth’s natural satellite evolved, but is also important for planning future prolonged manned missions to the Moon. Water could be collected by these space explorers not only for sustenance, but also to generate fuel that can be used to mount missions from the lunar surface. These missions could use the Moon as a launch pad for deeper exploration of the solar system, including Mars.
Li and his team’s theory links water on the Moon to the magnetic bubble surrounding the Earth called the magnetosphere. The magnetosphere protects our planet from high-energy charged particles released by the sun in the solar wind.
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When the solar wind hits the magnetosphere, it deforms this magnetic shield, creating a long magnetic tail on the side of the Earth facing away from the sun, the night side of the planet. This tail is aptly called a magnetotail. High-energy electrons and ions from the solar wind (and Earth itself) form a layer of plasma inside the magnetotail.
Then, as the Moon orbits the Earth, it passes through the magnetotail. As a result, just as the magnetosphere protects the Earth, the magnetotail protects the Moon from charged particles while allowing light to reach the lunar surface.
“This provides a natural laboratory to study the processes of lunar surface water formation,” Li said in a statement. “When the Moon is outside the magnetotail, the lunar surface is bombarded by the solar wind. There are almost no solar wind protons inside the magnetotail and water formation is predicted to drop to almost zero.”
He and the team used data collected between 2008 and 2009 by the Moon Mineralogy Mapper (MMM) instrument aboard the Chandrayaan 1 spacecraft to assess how water formation changes as the moon passes through the magnetotail.
“To my surprise, remote sensing observations showed that the formation of water in the Earth’s magnetotail is almost identical to the time when the Moon was outside the Earth’s magnetotail,” Li explained. “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, Li found that the radiation caused by high-energy electrons in the magnetotail shows effects similar to those caused by ions in the solar wind.
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Li initially started thinking about the interaction between the magnetotail and the Moon by considering the weathering processes on the lunar surface that occur when the Moon passes through the Earth’s magnetotail. This revealed that oxygen in the magnetotail rusts iron in the Moon’s polar regions.
“Overall, this discovery and my previous findings on the rusty lunar poles indicate that Mother Earth is strongly linked to its Moon in many unrecognized aspects,” Li added.
The team plans to follow up on this discovery by studying the plasma environment around the Moon and the water content at the lunar poles during different points of the Moon’s passage through the magnetotail.
This work will be conducted as part of the Artemis program which, as early as 2026, will also send the Artemis III mission to the Moon. This effort aims to return humanity to the moon for the first time in 50 years and send the first woman and first person of color to the lunar surface.
The team’s research was published September 14 in the journal Natural astronomy.