Scientists have long been interested in the non-magnetic nature of the moon today, and samples of rocks and regolith returned from the lunar surface suggest that they formed in the presence of a strong magnetic field. This magnetic field is so strong that it rivals that of Earth.

The moon may have been an occasional magnetic field powerhouse early in its history, a new study confirms, as scientists determine how a moon-sized object could generate such a powerful magnetic field. Evidence that the moon may be magnetic popped up when rocks returned to Earth were analyzed during NASA’s Apollo program from 1968 to 1972.

The study, published in the journal Nature Astronomy, suggests that the kind of internal convection that might have produced these strong magnetic fields could have been created through the massive rock layers that sink through the lunar mantle. The process likely produced intermittently strong magnetic fields during the first billion years of the moon’s history, the researchers said.

How is the magnetic field created?
“Everything we think about how planetary cores generate magnetic fields tell us that a moon-sized body shouldn’t generate as strong a magnetic field as Earth,” said Alexander Evans, assistant professor of Earth, Environment and Planets at Brown University. Science, who is also a co-author of the study.

Magnetic fields in planetary bodies are created by a process called a core dynamo, when slow heat dissipation causes convection of molten metal in the planet’s core. The constant stirring of the conductive material is what creates the magnetic field. This is the same way that Earth creates a magnetic field, which protects the surface from the sun’s most dangerous radiation.
Evans added that instead of thinking about how to continuously power a strong magnetic field over billions of years, perhaps there is a way to get high-intensity magnetic fields intermittently. “Our model shows how this happens, which is consistent with what we know about the Moon’s interior,” Evans said. For the core to be constantly magnetic, it needs to emit a lot of heat.

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