University of Hawai‘i at Mānoa, while pointing out that understanding the concentrations and distributions of water on the Moon is critical to understanding its formation and evolution, and to providing water resources for future human exploration, said the new study has been published in Nature Astronomy.
“This public impact research, led by Li, found that high energy electrons in Earth’s plasma sheet — an area of trapped charged particles within the magnetosphere, an area of space around Earth controlled by the planet’s magnetic field — are contributing to weathering processes on Moon’s surface and the electrons may have aided the formation of water on the lunar surface,” UH Mānoa said in a statement.
Water on the lunar surface: nearside (left) and farside (right) | Credit: Li, et al., 2023.
The magnetosphere protects Earth from space weathering and damaging radiation from the Sun. Solar wind pushes the magnetosphere and reshapes it, making a long tail on the night side. The plasma sheet within this magnetotail is a region consisting of high energy electrons and ions that may be sourced from Earth and the solar wind.
“Previously, scientists mostly focused on the role of high energy ions on space weathering of the Moon and other airless bodies. Solar wind, which is composed of high energy particles such as protons, bombards the lunar surface and is thought to be one of the primary ways in which water has been formed on the Moon,” UH Mānoa said.
Building on his previous work that showed oxygen in Earth’s magnetotail is rusting iron in the Moon’s polar regions, Li, an assistant researcher in the UH Mānoa School of Ocean and Earth Science and Technology, 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 solar wind but not the Sun’s light photons.
Graphic showing magnetosphere and plasma sheet | Credit: NASAGoddardAaron Kaase
“This provides a natural laboratory for studying the formation processes of lunar surface water. 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,” Li said.
Li and co-authors, who analysed remote sensing data from Chandrayaan-1’s Moon Mineralogy Mapper instrument between 2008 and 2009, specifically assessed the changes in water formation as the Moon traversed through Earth’s magnetotail, which includes the plasma sheet.
“To my surprise, the remote sensing observations showed that water formation in Earth’s magnetotail is almost identical to the time when the Moon was outside of the Earth’s magnetotail. 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,” Li said.
“…Altogether, this finding and my previous findings of rusty lunar poles indicate that the mother Earth is strongly tied with its Moon in many unrecognised aspects,” Li added.
In future research, Li aims to work on a lunar mission through NASA’s Artemis programmes to monitor the plasma environment and water content on the lunar polar surface when the Moon is at different phases during the traverse of the Earth’s magnetotail.