Small, frozen and silent, the moon has a surprising distribution of magnetic signatures across its dusty surface, and it’s not all easy to explain.
A new study led by geoscientist Jiang Guo, of the Institute of Geochemistry of the Chinese Academy of Sciences, can help us better understand the unusually strong magnetic field readings that are out of proportion with other characteristics of the moon, according to the RT report.
The Guo team analyzed lunar soil brought to Earth in December 2020 by the Chang’e 5 probe, and detected particles of a mineral known as magnetite, which is rarely seen in samples of lunar dust.
“The lunar magnetic anomalies have been a mystery since the Apollo era. Therefore, a deep understanding of the formation mechanism and distribution properties of magnetite on the Moon can provide a new perspective to explain the origin of magnetic anomalies in the lunar crust,” Guo and colleagues wrote in their published paper.
Magnetite Fe3O4, a strongly magnetic iron ore, was found in sub-microscopically spherical iron sulfide grains that resemble molten droplets. Further thermodynamic modeling indicates that magnetite is the result of large impacts on the lunar surface.
And for planetary scientists, the presence of magnetite is crucial: it can be used to track magnetic fields throughout history, as well as identify potential indicators of life, two of the hottest research discussions about any planet or moon.
Based on their findings, the researchers believe that magnetite can be widely distributed in the lunar soil as well, and it may now be easier to understand the moon’s unexplained magnetic anomalies if our models are adjusted to match the conclusions of this new study.
Unlike soil on Earth, lunar regolith is very low density, which means it contains an excess of electrons thanks to the moon’s constant bombardment by protons streaming in from the sun. This condition makes it difficult for iron to combine with oxygen to form ores.
This does not mean that it cannot happen, as small granules of magnetite were previously found in moon dust, but those studies suggested that magnetite was formed at relatively low temperatures – not under conditions of high pressure and high temperatures as a result of objects colliding with the surface of the moon, as well. This new work suggests.
“The features of the morphology (shape) of the iron sulfide grains and the distribution of oxygen indicate that a gaseous melt-phase reaction occurred during high-impact events,” the researchers explain.
Previous research had suggested that meteorites could have injected ferromagnetic material into the lunar surface upon impact, with the projectiles explaining at least some of the magnetic anomalies near the impact sites.
This new study goes further, finding that the fury of these impacts may also have transformed the material into microscopic magnetite, making it “an important source of ferromagnetic material on the lunar surface.”
In other words, the results indicate that the mineral is widely present on the surface of the Moon, which in turn changes our understanding of how the Moon has evolved over time.
The team suggests that the current magnetization of the lunar surface, along with the presence of these minerals, could help explain how the impacts of large objects led to a lunar magnetic field.
The researchers concluded that “these formation conditions lead to a correspondence relationship between the distribution of magnetic anomalies in the lunar crust and the distant ejections of large impacts.”