Chandrayaan-1 Data Suggests Earth’s Electrons May Be Contributing to Water Formation on Moon

Analyzing the concentrations and distributions of water on the Moon is important in understanding its origin and evolution. In addition, the presence of water on the Moon can also have the potential to provide water resources for future space explorations of humans.

Astronomers have long known that the moon has water, but how it got there remains a mystery. Some believe that the water was brought to our celestial neighbor by asteroids or comets, while others assume that it resulted from the chemical reactions on the Moon's surface. A new study suggests that water on the Moon may be formed by electrons that came from Earth.

Earth's Influence on Moon's Weathering

At the University of Hawai'i (UH) at Mānoa, a group of experts discovered the contributions of high energy electrons in Earth's plasma sheets to weathering processes on the surface of the Moon. These electrons could have aided the formation of water on the lunar surface.

Due to Earth's magnetism, our planet is surrounded by a force field known as the magnetosphere, which protects us from space weathering and solar radiation. The solar wind pushes and reshapes the magnetosphere, making a long tail on the night side. Within this magnetotail is a region called a plasma sheet made of high-energy electrons and ions that may be sourced from Earth and the solar wind.

During the previous years, astronomers mainly focused on the impact of high energy ions on the space weathering of the Moon and other airless celestial bodies. The solar wind is known to bombard the lunar surface, and since it is composed of high-energy particles like photons, it is believed to be one of the significant ways water has been formed on the Moon.

The Role of Earth's Magnetotail

At the UH Mānoa School of Ocean and Earth Science and Technology (SOEST), assistant researcher Shuai Li has been investigating the changes in surface weathering as the Moon passes through the magnetotail of the Earth. He referred to his previous work, which revealed that oxygen in Earth's magnetotail is rusting iron in the lunar polar region.

This area provides a natural laboratory for understanding the processes of forming water on the lunar surface. Every time the Moon is outside the magnetotail, its surface is bombarded with solar wind. When it is inside the magnetotail, there are almost no solar wind protons, and water formation is expected to drop to nearly zero.

With the help of his co-authors, Li analyzed the remote sensing data gathered by the Mineralogy Mapper instrument onboard the Chandrayaan-1 mission from 2008 to 2009. The data revealed that the formation of water in Earth's magnetotail is almost the same as when the Moon was outside the Earth's magnetotail. This means that in the magnetotail, additional sources of water could not be directly connected with the implantation of solar wind protons.

The discovery can help explain the origin of the water ice discovered in the permanently shaded regions of the Moon. In the future, Li plans to collaborate with NASA's Artemis programs to monitor the water content and plasma environment on the lunar polar surface.