The earth moon has two very different halves: its turned away side consists primarily of highlands with old, thick crust, but its front is characterized by extensive Maren with dark basalt lava. Now rehearsals that the Chinese moon probe Chang-E-6 brought back to Earth from the Monong side: This dichotomy may extend down to the lunar coat. Because in the basalt and coat frames from the South Pole Aitken basin, researchers have measured a significantly lower water content than in samples that, among other things, collected the Apollo missions on the side of the moon. This now provides exciting starting points for the search for the cause of these differences. You could go back to the catastrophic collision that once created the moon, but also to the impact on which the South Pole Aitken pool goes back.
According to common theory, the moon was created by the collision of the young earth with a sized protoplanet around 4.5 billion years ago. Large quantities evaporated rock and then froze again. The moon formed from these rubble. Based on this scenario and the lack of an atmosphere, the earth moon was long as “dry”. Water, one believed, could hardly be crust in the rock of the Lunar and the coat. But the rock samples of the Apollo missions already contradicted this assumption. Volcanic moon rock, which are from the moon coat, were discovered surprisingly high water content of up to 200 micrograms per gram. “This caused a change in the ideas to a relatively ‘wet’ lunar coat,” explain Huicun He from the Chinese Academy of Sciences in Beijing and her colleagues.
First analyzes of the coat rock of the turned away moon side
However, the previous data on the lunar coat rock are based almost exclusively on samples from the so-called Kreep terrans of the side of the moon facing us. This terrain characterized by volcanism is characterized by a relatively high content of rare earth metals, potassium, phosphorus and thorium. But what it looks like with the water content of the rock in the other two large geochemical provinces of the moon, the field-rich highland of the turned away side and the South Pole-Aitken basin, was previously unknown. However, it is striking that, unlike the Kreep terrans, these two provinces have a rather low thorium content. “Because thorium and water behave similarly in magmatic processes and preferably remain in the melt instead of crystallizing, the lunare could contain less water in the field-rich highlands and the South Pole-Aitken basin,” explain their presumption of the presumption.
The lunar fragments that the Chinese moon probe Chang’e-6 brought back from its landing site in the South Pole-Aitken basin of the turned moon side to Earth in the summer of 2024 have now given information. The team around HE examined 578 basaltic rocks from these samples, which go back to Magma from the Lunar coat. With the help of various chemical methods, the researchers determined the water content in tiny mineral inclusions of these rock crumbs. They also carried out isotope analyzes in order to determine the proportion of the “heavy” hydrogen in the water molecules. The analyzes showed that the APATITICKERNCHEN contained an average of 1500 micrograms of water per gram, while Ilmenit and Olivin grains, however, significantly less with 21 to 238 and 28 to 41 micrograms per gram. This results in a water content of the basalt mas from which these granules come from 15 to 168 micrograms per gram. However, in order to determine the overall water content of the original lunar mantle, further analyzes and calculations were necessary.
Drier than on the front
For the first time, these examinations provided information about how much water the lunar coat rock contains under the South Pole-Aitken basin. “According to our estimates, the coat source of the Chang’e-6 Basement contained a water content of 1 to 1.5 micrograms per gram,” report he and her colleagues. “It suggests that this mantle rock is drier than that of most samples from the facing side.” If this also applies to the lunare highlands of the turned away side, the lunare coat could be similarly heterogeneous as the crust rocks of the lunar surface – it would also be divided from geologically. This in turn could provide crucial indications of the early geological history of the earth’s drabant and the role of the moon-generating collision for this dichotomy. However, it would also be conceivable that this water poverty applies specifically to the moon coat under the South Pole-Aitken basin. The huge impact could therefore have heated the mantle rock so much that water and other fleeting substances mostly outline.
What is true can not yet be said due to the rock samples of only one landing point on the monasting side, as he and your team: “It is still unclear whether the dryer coat we documented here is spread under the South Pole Aitken basin or is over the entire faced side of the moon,” they write. In the near future, however, this could be clarified by missions by the United States Artemis Program and Chinese successor. These would then have to collect and return lunare stone samples from other places on the monong side.
Source: Huicun He (Key Laboratory of the Earth and Planetary Physics, Chinese Academy of Sciences, Beijing) et al., Nature, DOI: 10.1038/S41586-025-08870-X