On December 20, Chinese Academy of Sciences researchers, utilizing samples from the far side of the Moon brought back by Chang’e 6, discovered that the Moon’s magnetic field may have experienced a resurgence in intensity around 2.8 billion years ago. This contrasts with the previously held belief that the Moon’s magnetic field sharply declined around 3.1 billion years ago and remained at a low-energy state thereafter. This study not only provides the first-ever information on the ancient magnetic field of the Moon’s far side but also serves as a critical anchor point for understanding the evolution of the Moon’s magnetic field. The findings were published in the international journal Nature.
This paper reports measurements of the Moon’s ancient magnetic field at a unique time and location not covered by Apollo or Luna samples
Nature reviewer
The movement of conductive fluid in Earth’s liquid outer core acts like a “dynamo,” generating a magnetic field that envelops Earth, shielding it from cosmic radiation and protecting key elements of habitability, such as the atmosphere and water. This creates an environment conducive to life. Similarly, the Moon is believed to have once had a “magnetic field dynamo” akin to Earth’s.
Why it is significant?
Understanding the evolution of the Moon’s “magnetic field dynamo” is significant for uncovering its internal structure, thermal history, and surface environment. Satellite observations and surface measurements have shown that the Moon no longer has a global dipole magnetic field. Due to limitations in previously available lunar samples, existing data on the Moon’s ancient magnetic field intensity is concentrated around 3 billion years ago, with little constraint on the late-stage evolution of the Moon’s magnetic field. Moreover, prior data was derived solely from near-side lunar samples, leaving the ancient magnetic field of the far side largely unexplored. The lack of temporal and spatial distribution data on the Moon’s ancient magnetic field has led to considerable debate regarding the duration, geometry, and driving mechanisms of the Moon’s magnetic field.
Earlier research by the Chinese Academy of Sciences revealed that the primary eruption age of basalts in the Chang’e 6 samples is about 2.8 billion years (as determined by teams led by Academicians Li Xianhua and Xu Yigang). These samples, sourced from the Moon’s far side, fill a critical age gap and offer an unprecedented opportunity to study the spatial and temporal evolution of the Moon’s “dynamo.”
Zhu Rixiang & team
Recently, a research team led by Academician Zhu Rixiang and Associate Researcher Cai Shuhui from the Institute of Geology and Geophysics of the Chinese Academy of Sciences, in collaboration with the National Astronomical Observatories of the Chinese Academy of Sciences, conducted magnetic studies on four millimeter-sized basalt debris samples. The results revealed ancient magnetic field intensities ranging from approximately 5–21 μT, with a median value of ~13 μT.
This suggests that the “dynamo” may have reactivated after its initial sharp decline.
Unlike previous studies suggesting that the Moon’s “dynamo” remained in a low-energy state after a sharp decline 3.1 billion years ago, the ancient magnetic field intensities recorded in the Chang’e 6 basalt samples indicate that the Moon’s magnetic field rebounded around 2.8 billion years ago. This suggests that the “dynamo” may have reactivated after its initial sharp decline. The reactivation might have been caused by changes in the primary energy source or a resurgence of the initial driving mechanism.
Comparing “dynamo” models
Comparing different “dynamo” models, the magnetic field intensity recorded in the Chang’e 6 basalts aligns most closely with the magnetic field generated by the lunar magma ocean model. However, other energy sources that could supplement the Moon’s “dynamo” cannot be ruled out.
The Nature reviewers highlighted the groundbreaking originality of this study. They praised the team for conducting rigorous paleomagnetic analysis on the first-ever basalt samples from the Moon’s far side, providing high-quality, high-standard data. One reviewer noted:
This paper reports measurements of the Moon’s ancient magnetic field at a unique time and location not covered by Apollo or Luna samples, filling a billion-year gap in the lunar magnetic field record. It provides the first-ever measurements of the far side’s ancient magnetic field. The authors have conducted a historic study, making significant contributions to our understanding of the Moon’s magnetic field.
