The study of lunar soil samples brought back by the Chinese mission Chang’e 5 has finally made it possible to identify the nature of the water reservoir present in the subsoil of our satellite and to measure its impact on the cycle of moon water.
With the objective of returning to the LuneLune, the search for water on the surface of our satellite has undergone renewed interest. Being able to extract water directly from lunar rocks would be a definite advantage in future manned missions.
Forgotten, in fact, the idea that the Moon is totally “dry”. For about twenty years now, the presence of water has been confirmed by multiple studies, carried out both on the basis of observations orbitalsorbitals but also measures on sitein particular by the Chinese lander Chang’e 5.
A water cycle on the Moon
However, do not imagine water flowing on the surface of the Moon. Water is trapped here in the form of H molecules2O or OH within the rocks composing the lunar soil. As explained in a previous article (see below), the origin of this water remained to be clarified, as did its place in the Moon’s water cycle. Because as surprising as it may seem, there is indeed a water cycle on our satellite, although very different from the one we know on Earth. Observations have indeed shown that the equatorial regions deliver water to the surface of the Moon. Part then migrates to the polar regions thanks to temperature differences, while another part escapes into space. There is therefore a cycle described by phases of retention, release and recharging. However, this cycle requires the existence of a “buffer” reservoir in the lunar subsoil. A reservoir that was previously unidentified.
In a new study, researchers from the Chinese Academy of Science however, seem to have found it. To do this, they analyzed the samples brought back to Earth by Chang’e 5 and more particularly the glass balls produced during meteorite impacts on the surface of the Moon. These small fragments of molten regolith indeed contain water in a proportion which means that these rocks could represent the reservoir of water, perhaps making it possible to explain the water cycle of the Moon.
Water derived from solar winds and stored in glass beads
Isotope analyzes of thehydrogenhydrogen made it possible to show that the water contained in these glass beads came from the action of solar windssolar winds. The solar winds are indeed charged in protonproton H+. By impacting the lunar ground, the H+ protons react with the atomsatoms of oxygen present on the surface of the glass beads, producing water molecules. The small spheres of rock would thus act like a sponge, capable of absorbing water molecules, storing them, then releasing them through degassingdegassing.
Scientists have calculated that this reservoir would represent a total of between 300 million and 270 billion tons of water. The results were published in the journal Nature Geoscience.
The presence of water on the Moon confirmed by a Chinese mission on its surface
While the presence of water on the Moon had already been confirmed by orbital observations and sample analyses, an in situ measurement is now added to the list of proofs. It remains to specify the exact nature and origin of this water.
Article of Nathalie MayerNathalie Mayer published on January 16, 2022
There is water on the Moon. There are few who still doubt it today, as orbital observations and sample analyzes seem to provide proof of it. At the end of 2020, NASA even confirmed the presence of water molecules (H20) on the surface of our satellite. However, no measure on site had never yet been realized. But we must speak in the past because it is now done. Thanks to the Chinese lander Chang’e 5.
In December 2020, it landed on the Moon, north of the Ocean of StormsStorms. On one of basaltsbasalts the youngest — the site still dates back some two billion years — from our satellite. With the main objective of taking samples and bringing them back to Earth. But before that, he had time to point his lunar mineralogical spectrometer (LMS) on the regolithregolith surrounding.
Precious results, but to be specified
It is this instrument which made it possible to determine the water content of the rocks located in the field of vision of the lander. Using spectral reflectance measurements, the researchers were able to calculate that in some areas the regolith can contain up to 120 parts per million (ppmppm) water — in the form of hydroxyl (OH) or water molecules. While a rock they also analyzed contained slightly more. Almost 180ppm.
The researchers explain that the hydrogen necessary for the formation of water could have been brought there by the solar wind. The rock could well come from a unit basaltbasalt oldest and being ejected there. Its relatively high water content suggests a source hidden below the surface. And if the analyzes do not make it possible to discriminate between OH and H2O, they remain consistent with the preliminary analyzes of the samples reported by Chang’e 5Chang’e 5.
