Chang’e-6 lunar soil study identifies rare magnetic mineral
- Researchers studying lunar soil brought back by the Chang’e-6 mission have identified a rare magnetic mineral known as face-centred cubic γ-Fe inside tiny impact-glass particles.
- Scientists analyzing metallic iron inside impact glass from Chang'e-6 lunar soil identified γ-Fe for the first time in natural Moon samples.
- This tiny magnetic fossil may help us better understand the Moon's ancient magnetic history, said Dr.
Researchers studying lunar soil brought back by the Chang’e-6 mission have identified a rare magnetic mineral known as face-centred cubic γ-Fe inside tiny impact-glass particles. This nanoscale iron structure can preserve a stable magnetic signal, offering a microscopic fossil that sheds light on the Moon’s long-lost magnetic field.
Chang’e-6 Soil Samples Reveal Hidden Iron Phase
Scientists analyzing metallic iron inside impact glass from Chang’e-6 lunar soil identified γ-Fe for the first time in natural Moon samples. Professor Haifeng Du of the High Magnetic Field Laboratory at the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) directed the research, which was detailed in the Proceedings of the National Academy of Sciences (PNAS) on September 16.
This tiny magnetic fossil may help us better understand the Moon’s ancient magnetic history,
said Dr. Long Li from HFIPS, a member of the research team.
To examine the samples, the research team used focused ion beam preparation, transmission electron microscopy, and chemical analysis. These techniques revealed numerous nanoscale iron particles embedded throughout the glassy material, with γ-Fe emerging as the dominant form of iron in the two impact-glass samples studied.
Impact Conditions Stabilize Nanoscale Iron
Under normal conditions, γ-Fe is stable only at high temperatures and typically changes into another form known as α-Fe as material cools. The unusual conditions produced by impacts on the Moon allow γ-Fe to survive at the lunar surface.
According to researchers, several variables contribute to the structural stability of the material, such as trace amounts of carbon alongside other elements, the swift chilling of impact-generated molten substance, and the safeguarding effect of the surrounding glassy matrix. Using off-axis electron holography to investigate individual γ-Fe nanoparticles, the team found that relatively large γ-Fe particles could form a stable single-vortex magnetic state and retain a consistent magnetic response when exposed to an external magnetic field.
Debate Over Early Dynamo and Ancient Field Strength
The discovery arrives amid a decades-long scientific discussion regarding the Moon’s ancient magnetic field. While the Moon no longer generates a global magnetic field today, about 4.25 billion years ago it possessed a powerful core dynamo with a field strength comparable to or even exceeding modern Earth’s. That magnetic field completely shut down as the interior cooled and core crystallisation ceased.
The debate over whether an early dynamo existed stretches back to the 1970s when Apollo missions first returned lunar rocks showing signs of having recorded a magnetic field, according to Anna Mittelholz, a lecturer at the Swiss Federal Institute of Technology Zurich (ETH Zurich). While some recent analyses of Apollo samples found no magnetic signal for parts of that period, other research published in Science Advances on September 23 found an intensely magnetized rock body in the Dewar region on the far side of the Moon, supporting the dynamo theory and suggesting a field strength stronger than 10 microtesla.
Future Analysis of Lunar Magnetic Minerals
Because α-Fe and γ-Fe arise under distinct circumstances and display differing magnetic traits, each type may potentially preserve records from different phases of lunar impact events. Additional studies are necessary to fully ascertain what these minerals can uncover regarding the ancient lunar magnetic field and its progression over time.