Earth's magnetotail could be forming water on the Moon

Data collected by India's Chandrayaan-1 mission suggests that high-energy electrons in Earth’s magnetotail are forming water on the lunar surface.
Chris Young
A 3D rendering of the Moon.
A 3D rendering of the Moon.

Thibault Renard / iStock 

A new discovery by a team led by the University of Hawai‘i at Mānoa planetary scientist Shuai Li could help explain the origin of water ice in shadowed lunar craters.

They discovered that high-energy electrons in Earth's plasma sheet contribute to weathering processes on the Moon's surface. These may have led to the formation of water on the lunar surface, a press statement reveals.

Earth's magnetotail interacts with the lunar surface

Earth's plasma sheet is an area surrounding our planet within the magnetosphere that is made up of trapped charged particles. The magnetosphere, which is controlled by our planet's magnetic fields, protects Earth from space weather and radiation from the Sun.

Solar wind changes the magnetosphere's shape, giving it a long tail on the Earth's night side. This trailing invisible tail attached to Earth is known as a magnetotail.

The researchers, who published their findings in a paper in the journal Nature Astronomy, built on previous work showing that Earth's magnetotail rusts iron in the Moon's polar regions.

They investigated the changes in surface weathering as the Moon passes through Earth's magnetotail, which is known to periodically shield the Moon from solar wind.

"This provides a natural laboratory for studying the formation processes of lunar surface water," Li explained in the statement. "When the Moon is outside of the magnetotail, the lunar surface is bombarded with solar wind. Inside the magnetotail, there are almost no solar wind protons and water formation was expected to drop to nearly zero."

Analyzing the lunar surface

Li and his team analyzed remote sensing data collected by the Moon Mineralogy Mapper instrument aboard India's Chandrayaan 1 mission between 2008 and 2009.

They focused on the changes in water formation that occurred when the Moon was interacting with Earth's magnetotail.

"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," Li said. "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," Li continued.

Li and his team will continue to research the Moon's interactions with Earth. They hope to work on a lunar mission via NASA's Artemis program, allowing them to monitor the plasma environment and water content on the Moon's polar regions while it is affected by Earth's magnetotail.

With NASA and other space agencies looking to establish a permanent colony on the lunar south pole, this type of work will become increasingly important as it helps to better understand a region of the Moon that is so far relatively unexplored — one with potentially vast amounts of drinkable water that would be crucial to the creation of lunar habitats.

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