Earth Is Doing Something Incredible: Helping the Moon Form Water

Tim Newcomb
Mon, September 25, 2023 

Earth Helping the Moon Form WaterGrant Faint - Getty Images

High-energy electrons from Earth’s magnetic field act like solar wind protons to help form water on the Moon.

The Moon interacts with Earth’s magnetic field, a key piece in understanding water formation on the Moon.

Learning fresh ways in which the Earth helps the Moon form water could help future explorations on the planet.

Earth has so much sway in our little corner of the Solar System that the forming of water on the Moon is directly tied to its magnetic field. Now, scientists know even more about the importance of these Earth-to-Moon interactions, and have discovered an entirely new way that Earth helps form water on the Moon.

In a new study from the University of Hawaii at Mānoa—published in Nature Astronomy—researchers show how Earth’s magnetosphere helps the weathering processes along on the Moon’s surface, and just how important high-energy electrons are in the process of forming water.

To understand the water-forming element, though, researchers first had to understand data about solar wind.

Earth’s magnetosphere protects us from the Sun’s unrelenting radiation. Solar wind can affect this magnetosphere, reshaping it and creating a “magnetotail” pointing away from the Sun. The Moon, in turn, can spend 27 percent of its time within the tail—a spot that blocks roughly 99 percent of solar wind.

Previously, solar wind was given nearly carte blanche credit for the forming of water molecules on the Moon. Full of high-energy particles, solar wind brings the Moon hydrogen ions, and the force of the wind kickstarts an interaction with oxygen to form water.

But solar wind can’t take all the credit any longer for the water, according to the study’s lead author Shuai Li, planetary scientist at the University of Hawaii. The research shows that even when the solar wind isn’t present, water formation is still running rampant.

“When the Moon is outside the magnetotail, the lunar surface is bombarded with solar wind,” Li said in a news release. “Inside the magnetotail, there are almost no solar wind protons and water formation was expected to drop to nearly zero. 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.”

This was a significant—and unexpected—finding. “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,” Li said. “In particular, radiation by high-energy electrons exhibits similar effects as the solar wind protons.”

Li believes that the new discovery shows that Earth and the Moon may be linked together even more intrinsically than previously believed, and “in many unrecognized aspects.”

The data for the current study comes from the Moon Mineralogy Mapper instrument onboard India’s Chandrayaan 1 mission from 2008 to 2009. In the future, Li hopes to work with NASA’s Artemis programs to monitor the plasma environment and water content in the polar region of the lunar surface.

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