A new analysis of lunar samples collected by China’s Chang’e-5 mission has unveiled that the moon possessed a weak yet persistent dynamo magnetic field approximately 2 billion years ago.
Understanding the strength, structure, and evolution of the lunar magnetic field is pivotal for unraveling the moon’s internal structure, thermal history, and surface environment. The discovery sheds new light on our closest celestial neighbor’s midlife, a period that has remained largely unexplored.
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 region in the moon’s mid-latitudes. These rocks offer a rare glimpse into the moon’s magnetic history between 3 and 1 billion years ago, filling a significant gap in lunar research.
“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,” said Cai Shuhui, a corresponding author of the study. The study was published on Thursday in Science Advances, where it was featured as the cover story.
This finding suggests that the lunar dynamo—the mechanism by which a celestial body generates a magnetic field—lasted at least until the moon’s middle years. The researchers proposed that ongoing thermal convection in the moon’s deep interior may have provided extra heat for volcanic activity before the magnetic field completely vanished.
The power driving this magnetic field could stem from processes such as 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,” said Cai. “This offers a benchmark for research into space weathering and volatile materials like water on the lunar surface during the moon’s midlife.”
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. This 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, Cai noted.
In November last year, 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 25th 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.
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Chang'e-5 samples reveal moon's weak but persistent magnetic field
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