2023-09-18 17:13:05
You might not think it at first, but the lunar soil contains large quantities of water. If it is now well established that solar winds are at the origin, a new study shows that the terrestrial magnetosphere could also play a very important role.
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Its gray and dusty landscape does not suggest this, and yet, despite the absence of an atmosphere, the Moon does contain water. In rather impressive quantities in fact. However, water is present in a very different way from what we know on Earth. It is in fact trapped within the minerals that make up lunar regolith. New explorations of the Moon have also revealed the existence of a lunar water cycle. In this cycle, solar winds would play a major role in the formation of hydrated molecules. They are in fact charged with protons (H+) which, upon striking the lunar soil, cause the formation of water molecules by reaction with the oxygen atoms present in the minerals.
A new study now goes further by establishing a link between the formation of these water molecules and the Earth’s magnetosphere.
Water formed despite the absence of solar winds
Several observations still intrigued scientists. Because if solar winds are the origin of water on the Moon, how can we explain the presence of water ice in regions that are perpetually in shadow? In addition, the illuminated side of our satellite spends approximately 27% of time per day in what is called the Earth’s magnetotail, an area of space protected from the solar wind by the action of our Planet’s magnetic field. However, while solar winds are reduced by almost 99%, no clear decrease in the quantity of lunar water could be observed in correlation with this phenomenon.
The magnetosphere represents the force field created by the Earth’s magnetic field. It surrounds the planet, protecting it from the Sun’s radiation. But the magnetosphere does not represent a sphere. The solar winds in fact give it an elongated shape, stretching it into a long tail towards the “night” side. This magnetotail has several regions, notably what is called the plasmasheath (or plasma sheet). It is a hot zone composed of thick plasma containing a high density of high-energy ions and electrons. They result from the interaction between solar winds and the Earth’s magnetosphere.
Water formed by electrons in the Earth’s magnetosphere
Researchers were therefore interested in the formation of water on the lunar surface as a function of the Moon’s passage through the Earth’s magnetotail, where solar winds and their flow of protons are almost non-existent. By analyzing the data collected by the Indian probe Chandrayaan 1 between 2008 and 2009, the researchers then understood that there was almost no difference between the time when the Moon was outside the magnetotail (and therefore subject to solar winds) and the one where it was inside, indicating that protons carried by solar winds were not the only process leading to the formation of water on the Moon’s surface.
It would indeed appear that the high-energy electrons making up the plasmasheath of the Earth’s magnetosphere are also capable of producing water on the surface of our satellite. The terrestrial magnetosphere would therefore play just as important a role in this process as the solar winds. These results were published in the magazine Nature Astronomy.
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