Mantle of the moon 'colder' on its far side

Chinese scientists have recently published a new significant finding that will help to better understand the moon's history and its hemispheric dichotomy, or the dramatic difference between the lunar near and far sides.

According to a joint statement released on Monday by the China National Space Administration and the China Atomic Energy Authority, a group of researchers from the Beijing Research Institute of Uranium Geology, a China National Nuclear Corp subsidiary, Peking University and Shandong University have found, for the first time, that the lunar mantle on the far side is "colder" than that on the near side.

Researchers made the discovery after analyzing lunar dust retrieved from the far side of the moon by the Chang'e 6 robotic probe.

The finding, which was published in the academic journal Nature Geoscience on Sept 30, will further deepen the understanding of the moon's hemispheric dichotomy, provide petrological, geochemical and other scientific evidence for the temperature difference between the lunar mantle on the near and far sides, and present key scientific data for research on lunar evolution and the characteristics of the hemispheric dichotomy, according to the statement.

This also marks a new achievement in the cross-disciplinary collaboration between Chinese nuclear and space scientists, following their discovery of the sixth lunar mineral — Changesite-(Y) — in late 2022, the statement noted.

Located beneath the lunar crust, the lunar mantle is the largest component of the moon in terms of volume, and the moon's ancient volcanic activities were formed by the upward movement of mantle materials. Therefore, the internal characteristics of the moon, such as the lunar mantle, are crucial for research on lunar evolution, the statement added.

In their study, scientists used a variety of methods to conduct detailed analysis of the lunar samples brought back by the Chang'e 6 probe.

By analyzing the compositions of typical minerals, including clinopyroxene and plagioclase, in the lunar regolith basalt samples, they calculated the crystallization temperature and pressure using three different thermobarometers. To ensure the scientific validity of the results, the team simulated the crystallization process of Chang'e 6 samples through a petrological model.

The four independent methods yielded consistent results — the crystallization temperature of the basalt samples is about 1,100 C, approximately 100 C lower than that of samples from the near side.

The researchers also reconstructed the chemical composition of the moon's original magma and calculated the potential temperatures of the lunar mantle. They found that the potential temperature of the lunar mantle on the far side is about 100 C lower than that on the near side. In addition, the research team used lunar remote-sensing data to conduct verification and analysis on a larger regional scale.

"Collectively, our findings demonstrate that the lunar far side mantle is relatively colder than the near side mantle, consistent with the hemispherical differences in crustal thickness and heat-producing element distribution, and provide constraints on the thermal evolution of the moon and the origin of its global asymmetry," the scientists wrote in their Nature Geoscience article.

Li Ziying, a senior scientist and one of the research leaders, said that studying the physical and chemical differences between the lunar near and far sides not only enables scientists to deepen their knowledge about the moon itself, but also offers insights into Earth's evolution.

The Chang'e 6 mission, representing the world's first attempt to bring samples from the far side of the moon, was launched in May 2024 from the Wenchang Space Launch Site in Hainan province.

The mission successfully concluded after 53 days of sophisticated maneuvers, retrieving a total of 1,935.3 grams of samples from the far side.