Something hidden inside the Moon may be behind its mysterious rotations: Scientists have a theory

The face of the Moon is famous for its gray, pockmarked color, but did you know that if you turn a telescope to our planet’s neighboring satellite, you’ll also see bright spots dotting the surface?

Ever since these strange features known as lunar gyres were first noticed in the 1600s, scientists have wondered where they came from.

To this day, light-colored areas like that of the well-known Reiner Gamma rotation (pictured below) remain a mystery.

A new study by scientists at Stanford University and Washington University in St. Louis (WUSL) provides evidence of a new explanation.

Unlike planet Earth, the Moon no longer generates a global magnetic field to protect it from the Sun’s charged particles. This means that when solar winds collide with the lunar surface, they turn the rock darker over time due to chemical reactions.

That said, some pockets on the Moon appear to be protected by mini magnetic fields.

So far, every lunar orbit with light shadows scientists have found coincides with one of these local magnetic fields. And yet not all rocks within them are reflective, nor do all magnetic fields on the Moon contain spins.

So what is happening on Earth (or, rather, on the Moon)?

Several recent studies have explained the confusing results by arguing that micrometeorite impacts on the Moon can propel charged dust particles, and wherever these particles land, a local magnetic field barrier is created and the solar wind is reflected.

But researchers at Stanford and WUSL now dispute that hypothesis. They argue that another force has ‘magnetized’ the lunar gyres, deflecting solar wind particles.

“Impacts can cause these kinds of magnetic anomalies,” admits planetary scientist Michael Krawczynski at WUSL.

“But there are some spins where we’re just not sure how an impact could create that shape and that size of thing.”

Krawczynski suggests that forces from below the crust may also be at work. “Another theory is that you have lava underground, slowly cooling in a magnetic field and creating magnetic anomalies.”

Just beneath the surface of the Moon, scientists have found radar evidence of what once was molten rock. These underground rivers of cooled magma indicate a period of volcanic activity billions of years ago.

Using a model of these magma cooling rates, Krawczynski and his colleagues examined how a titanium-iron oxide mineral called ilmenite—abundant on the Moon and commonly found in volcanic rocks—could produce a magnetizing effect.

Their experiments show that under the right conditions, slow cooling of ilmenite can stimulate grains of metallic iron and iron-nickel alloys within the Moon’s crust and upper mantle to produce a powerful magnetic field.

This effect, the researchers conclude, “could explain the strong magnetic regions associated with lunar rotation.”

“If you’re going to make magnetic anomalies with the methods we describe, then the underground magma has to be high in titanium,” Krawczynski says.

“We’ve seen hints of this iron-forming reaction in lunar meteorites and lunar samples from Apollo. But all those samples are surface lava flows, and our study shows that subsurface cooling must significantly enhance these metal-forming reactions.”

Much of what we know so far about the Moon’s localized magnetic fields comes from an orbiting spacecraft that can measure the effect using radar. But to really understand what’s going on, we need to drill directly into the lunar surface.

This is exactly why NASA is sending a rover into Reiner Gamma orbit in 2025 as part of their Lunar Vertex mission.

In just a few more years, scientists may have the evidence they need to put an end to this mystery.

The study was published in Journal of Geophysical Research: Planets.