Water found on the Moon may actually come from Earth

Researchers from the University of Hawai‘i (UH) at Mānoa have revealed that high energy electrons in Earth’s plasma sheet are influencing the Moon’s weathering processes, and might be pivotal in the formation of water on the moon.

Significance of water on the moon

Understanding the Moon’s water content — its concentration, distribution, and origin — is paramount. Not only does it offer insights into the Moon’s formation and evolution, but it’s also a potential resource for human exploration missions.

The newfound correlation might even shed light on the mysterious water ice found in the Moon’s perpetually shaded regions.

The protective magnetosphere

The Earth is surrounded by a protective force field called the magnetosphere, a result of its magnetic field. This magnetosphere acts as a shield against space weather and harmful solar radiation.

The Sun’s solar wind — a stream of charged particles — affects the magnetosphere, reshaping it and creating an extended tail on its night side, known as the magnetotail. This tail consists of the plasma sheet, which is a region teeming with high-energy electrons and ions possibly sourced from both Earth and the solar wind.

Historically, scientific discourse largely revolved around the role of high-energy ions, primarily from the solar wind, in the space weathering of the Moon and other airless celestial bodies.

The solar wind is mostly comprised of high-energy particles like protons. It is believed to be a main mechanism that forms water on the Moon.

Earth’s magnetotail: A natural laboratory

Shuai Li, the assistant researcher at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST) and the study’s lead, previously highlighted how oxygen in Earth’s magnetotail contributes to the rusting of iron in the Moon’s polar regions.

Building on that work, Li wanted to explore how lunar surface weathering changed as the Moon passed through the Earth’s magnetotail. This area nearly shields the Moon from solar wind but doesn’t block sunlight.

Li explained that the magnetotail offers a “natural laboratory” for their investigations. When the Moon is outside the magnetotail, it is continuously bombarded by the solar wind. However, when inside the magnetotail, the presence of solar wind protons significantly diminishes, leading to an assumption that water formation would decrease dramatically.

However, upon analyzing remote sensing data from India’s Chandrayaan 1 mission between 2008 and 2009, the results were startling. The observations revealed that water formation inside Earth’s magnetotail is nearly identical to periods when the Moon was outside this region.

Li noted, “This indicates that, in the magnetotail, there may be additional formation processes or new water sources not directly linked to solar wind protons.” Specifically, the radiation effects of high-energy electrons within the magnetotail are remarkably similar to those of the solar wind protons.

Li further emphasized the intertwined relationship between Earth and its Moon, stating, “Altogether, this finding and my previous findings of rusty lunar poles indicate that the mother Earth is strongly tied with its Moon in many unrecognized aspects.”

Future lunar water research

Looking ahead, Li hopes to collaborate on a lunar mission under NASA’s Artemis programs. The goal? To closely monitor the plasma environment and water content on the lunar polar surface as the Moon undergoes various phases while traversing Earth’s magnetotail.

This study underscores the intricate relationship between Earth and its celestial companion. It broadens our understanding of the dynamic processes that shape and influence our natural satellite.

The study was recently published in Nature Astronomy.

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