A new analysis of samples collected by China’s Chang’e-5 mission has revealed that the moon possessed a weak yet active dynamo magnetic field approximately 2 billion years ago.
Understanding the strength, structure and evolution of the lunar magnetic field is crucial for unraveling its internal structure, thermal history, and surface environment.
Researchers, led by scientists from the Institute of Geology and Geophysics (IGG) under the Chinese Academy of Sciences (CAS), analyzed nine basalt samples returned by Chang’e-5 from the Oceanus Procellarum in the moon’s mid-latitudes.
These rocks offer a unique opportunity to explore the moon’s magnetic history from 3 to 1 billion years ago, a period that remains underexplored. This gap raises the intriguing question of whether the moon experienced a long-lasting “dynamo” effect.
The results show that the moon had a weak dynamo magnetic field during this period, measuring around 2 to 4 microteslas – less than 10 percent of Earth’s current field strength, according to the study published Thursday in Science Advances, where it was featured as the cover story.
This finding helps fill a major gap in our understanding of the moon’s magnetic evolution and suggests that the lunar dynamo lasted at least until its middle years, said Cai Shuhui, a corresponding author of the paper.
The researchers also suggested ongoing thermal convection in the moon’s deep interior, which may have provided extra heat for volcanic activity before the magnetic field completely vanished.
The power driving the magnetic field could stem from processes like the lunar core’s crystallization, wobble and the descent of dense primordial materials, according to the study.
The weak magnetic field detected in the Chang’e-5 samples points to the presence of a protective magnetic shield during this time, offering a benchmark for research into space weathering and volatile materials such as water on the lunar surface in the moon’s midlife, said Cai.
Additionally, the research team published a study in the journal Nature last month, indicating an unexpected resurgence in the strength of the moon’s magnetic field 2.8 billion years ago. The discovery was based on rock samples collected from the moon’s far side by the Chang’e-6 lunar probe.
These two studies together suggest that the moon’s magnetic field not only persisted into its midlife but may also have fluctuated during that time, said Cai.
In November 2024, an IGG team reported two volcanic events that occurred on the moon’s far side 2.8 billion years ago and 4.2 billion years ago. Another study confirmed that the low-titanium samples collected by Chang’e-6 are approximately 2.83 billion years old, providing evidence of volcanic activity on the far side of the moon.
On June 25 last year, the Chang’e-6 lunar probe returned to Earth with 1,935.3 grams of lunar samples collected from the moon’s previously unexplored far side. Similarly, the Chang’e-5 probe, which returned on December 17, 2020, retrieved 1,731 grams of lunar samples, consisting primarily of rocks and soil from the lunar surface.