Yesterday, the reporter learned from the Institute of Physics of the Chinese Academy of Sciences that the Chinese scientific research team found a mineral crystal rich in water molecules and ammonium on the moon in the lunar samples brought back by Chang'e-5. This discovery marks the first discovery of molecular water in the return lunar soil, while revealing the true form of water molecules and ammonium on the Moon.
The discovery of hydrated minerals on the lunar surface marks a major breakthrough in the study of lunar water and ammonium, and also provides new possibilities for the development and utilization of lunar resources in the future. The results have been published online in Nature · Astronomy.
The existence of water on the moon has been a core issue in lunar scientific research and resource utilization for decades. Historically, no water-bearing minerals have been found in the lunar soil collected by the Apollo missions, which at one time led the scientific community to believe that the moon was a dry desert. Until recent years, a series of remote sensing missions have found evidence of the existence of lunar water in the permanent shadow areas of the lunar poles and in parts of the lunar illuminated areas. Using highly sensitive characterization techniques, PPM (parts per million) of "water" (hydroxyl OH-) has been found in some Apollo samples. So far, no conclusive evidence of the existence of water molecules has been found in the returned lunar soil. The presence of molecular water on the lunar surface has also been unknown.
The research was completed by researcher Chen Xiaolong of the Institute of Physics of the Chinese Academy of Sciences, associate researcher and doctoral student Hao Munan of the Institute of Physics of the Chinese Academy of Sciences, associate professor Guo Zhongnan of the University of Science and Technology Beijing, engineer Yin Bohao of Tianjin University, and researcher Ma Yunqi of the Qinghai Salt Lake Institute of the Chinese Academy of Sciences.
Through high-precision single crystal diffraction and chemical analysis, the researchers determined that the mineral has the molecular formula (NH4,K,Cs,Rb) MgCl3·6H2O, which is a hydrated mineral.
Its structure contains up to six crystalline waters, and the mass ratio of water molecules in the sample is as high as 41%.
Infrared and Raman spectroscopy can clearly observe the vibrational peaks of water molecules and ammonium, and charge density analysis can resolve hydrogen in water molecules.
According to Chen Xiaolong, the crystal structure of the mineral is the same as that of a rare crater mineral found on Earth in recent years. On Earth, these minerals are formed by the interaction of hot basalts with volcanic gases rich in water and ammonia, suggesting a close connection between lunar water and volcanic activity.
To ensure the accuracy of this finding, the researchers performed rigorous chemical and chlorine isotope (37Cl/35Cl) analysis. Experimental data show that the Cl isotopic composition of this mineral is significantly different from that of Earth minerals, and its δ37Cl value is as high as 24‰, which is consistent with the minerals on the Moon.
The analysis of the chemical composition and formation conditions of this mineral further ruled out earth pollution or rocket exhaust as a source of this hydrate. The presence of this hexahydrate mineral forms an important constraint on the composition of the lunar volcanic gases. Based on thermodynamic analysis, the lower limit of water content in the lunar volcanic gas at that time was comparable to that of the Lengai volcano, which is currently the driest volcano on Earth, which is of great significance for our understanding of the evolution of the Moon. These discoveries reveal a complex history of volcanic degassing on the Moon.
The discovery of this hydrated mineral also sheds light on the moon about a possible form of water molecule on the moon – hydrated salts. Unlike volatile water ice, this hydrate is very stable at high lunar latitudes (the Chang'e-5 sampling site). This means that even in the vast lunar sunlit area, such stable hydrated salts may exist, providing a broader prospect for the utilization and exploration of lunar resources.
Associate researcher Jin Shifeng and Hao Munan are the co-first authors, and researcher Chen Xiaolong is the corresponding author. The Center for Lunar Exploration and Space Engineering provided lunar soil samples for the study (CE5C0400).