Glassy grains on the lunar surface form a previously unknown water reservoir there, reports a team around the Geophysicist Hu Sen of the Beijing-based Chinese Academy of Sciences in NatureGeoscience. The granules act like a sponge in the moon’s water cycle. In total, the study authors estimate that there are between 100 million and 100 billion tons of water in such glass grains on the moon. Lake Constance stores a water mass of around 50 billion tons.
The researchers came across the discovery of water while examining rock samples that the Chinese space probe Chang’e 5 from her flight to the moon in early December 2020. The realization that there are water-storing glass grains on the earth’s satellite is completely new, but not: In 2008, a team led by the late geochemist Erik Hauri first detected water on the moonin soil samples still from the Apollo-Missions came from. Even then, the water was hidden in glass stones.
Future moon missions could use the water to produce oxygen, for example
The group around Hauri had assumed that the glass grains are of volcanic origin and that there could be other water deposits inside the moon. As a result, people looked at the spectroscopic data from moon probes with a sharpened eye. With success: water could be detected in several places. Where there is little sunlight – at the poles of the moon – there was a particularly large amount of water and ice near the surface. The fact that the water content fluctuated depending on the solar radiation indicated a water cycle. So far, however, it has been unclear how exactly this works.
The glass grains analyzed by Hu and colleagues are believed to have arrived on the moon through asteroid impact. However, the glass chunks are still anhydrous upon impact. The water arrives later, in the form of charged hydrogen nuclei, which are carried to the moon by solar wind and react with oxygen from dust particles to form water molecules. A similar process could be the origin of the oceans on Earth. The contribution of solar winds to the formation of the “blue planet” has recently been discussed.
In contrast to the earth, however, the moon has practically no atmosphere. The fact that the water cycle still works on the moon can be explained with the help of a buffering reservoir. The new find suggests that glass grains on the lunar surface are capable of storing and releasing water, Hu says. Through diffusion, the solar wind water can also reach the inner layers of the moon. And the moon water should also have a practical use: future moon missions such as artemis could possibly use it, for example to produce oxygen.