https://spc.jst.go.jp/news/240705/topic_2_05.html
According to the Institute of Physics, Chinese Academy of Sciences, researchers from the institute, in collaboration with researchers from other institutions such as Beijing University of Science and Technology, discovered an unknown mineral crystal called “ULM-1” rich in water molecules and ammonium in lunar samples brought back by the lunar probe “Chang’e-5”.
Whether or not there is water on the Moon is extremely important for research into the evolution of the Moon and for resource development. In the Apollo sample studies taken between 1969 and 1972, no minerals containing water were found, and the absence of water on the Moon became the basic premise in the academic community, which had an important impact on issues such as the evolution of lunar volcanoes and the understanding of the origin of the Moon and the Earth. In 1994, researchers observed both poles of the Moon with the Clementine probe and suggested that water ice may exist in the soil of the “permanent shadow” of the polar regions.
In 2009, the lunar mineral mapping device installed on the Chandrayaan-1 discovered that signals of hydroxyl groups or water molecules caused by the solar wind existed on the Moon’s surface. In the same year, the Lunar Observation and Remote Sensing Satellite crashed into the permanent shadow of the Moon at a speed of 2.5 kilometers per second. Remote sensing surveys of the dust at the time of the impact showed water signals.
Recent remote sensing data has shown traces of water molecules in illuminated areas of the Moon, and scientists have used highly sensitive characterization techniques to find “water (H+, OH- or H2O)” on a scale of one part per million in some glass and minerals in Apollo lunar samples taken at that time, but there was no conclusive evidence of the presence of water molecules.
In this study, single crystal diffraction and chemical analysis were used to discover that these lunar water and ammonium appear in the form of a hydrated mineral called (NH4,K,Cs,Rb)MgCl3·6H2O. The molecular formula of this mineral contains six crystal waters, and the mass ratio of water molecules in the sample reaches 41%. Infrared and Raman spectra clearly show characteristic peaks from water molecules and ammonium. The crystal structure and composition of ULM-1 are similar to rare crater minerals recently discovered on Earth. On Earth, these minerals were formed by the interaction of hot basalt with volcanic gases rich in water and ammonia, providing new clues about the source of lunar water and ammonia.
To prove the accuracy of this discovery, the study carried out rigorous chemical and chlorine isotope analysis. Nanoscale secondary ion mass spectrometry data showed that the CI isotope composition of the mineral was significantly different from that of terrestrial minerals and consistent with that of lunar minerals. The researchers analyzed the chemical composition and formation conditions of the mineral and ruled out terrestrial pollution or rocket exhaust as the source of this hydrate. The presence of this mineral provides important constraints on the composition of lunar volcanic gases. Thermodynamic analysis showed that the lower limit of the water content of lunar volcanic gases at that time was equivalent to Lengai volcano, the driest volcano on Earth today. This reveals a complex history of lunar volcanic degassing, which is of great significance for exploring the evolutionary process of the moon.
The discovery of this hydrated mineral revealed the possibility that water molecules on the moon may exist in the form of hydrated salts. Unlike water ice, which is easily volatile, this hydrate is very stable even at high latitudes on the moon (the sample collection site of Chang’e-5). This means that stable hydrated salts can exist even in widely illuminated areas of the moon, opening up new possibilities for the future development and utilization of lunar resources.