The face of the Moon is known for its gray, diseased skin, but did you know that if you turn your binoculars to our planet’s neighboring moon, you’ll also see bright spots marring the surface?
Ever since these strange formations, known as lunar vortices, were first spotted in the 1600s, scientists have wondered where they came from.
To this day, bright regions such as the region of the famous Reiner Gamma vortex (pictured below) remain a mystery.
A new study by researchers from 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 darken the rock over time due to chemical reactions.
This means that some pockets on the moon appear to be protected by mini magnetic fields.
Until now, all scientists have found in the light shadowed lunar vortices coincides with one of these local magnetic fields. And yet not all rocks in them are reflective, nor do all magnetic fields on the Moon contain eddies.
So what is happening on Earth (or rather, the Moon)?
Some recent studies have explained the puzzling results by arguing that micrometeorite impacts on the Moon can throw up 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 are now challenging that hypothesis. They argue that some other force “magnetized” the lunar eddies and deflected the solar wind particles.
“Impacts could cause these types of magnetic anomalies,” admits WUSL planetary scientist Michael Krawczynski.
“But there are some eddies where we’re just not sure how an impact could create such a shape and size of thing.”
Krawczynski suggests that forces from beneath the crust could also be at work. “Another theory is that you have lava underground that slowly cools in the magnetic field and creates a magnetic anomaly.
Just below the moon’s surface, scientists have found radar evidence of what was once flowing molten rock. These underground rivers of cooled magma indicate periods of volcanic activity billions of years ago.
Using a model of these magma cooling rates, Krawczynski and his colleagues investigated how a titanium-iron oxide mineral called ilmenite—abundant on the Moon and commonly found in volcanic rocks—might produce a magnetizing effect.
Their experiments show that under the right conditions, slow cooling of ilmenite can stimulate metallic iron and iron-nickel alloy grains in the lunar crust and upper mantle to create a strong magnetic field.
This effect, the researchers conclude, “could explain the strong magnetic fields associated with the lunar vortex.”
“If you’re going to create magnetic anomalies with the methods we’re describing, then the underground magma has to be high in titanium,” says Krawczynski.
“We’ve seen hints of this iron-forming reaction in lunar meteorites and in lunar samples from Apollo. But these samples are all surface lava flows, and our study shows that cooling underground should greatly enhance these metal-forming reactions.”
Much of what we know so far about the Moon’s localized magnetic fields comes from orbiting spacecraft that can measure the effect with radar. But to really understand what’s going on, we need to drill directly into the lunar surface.
That’s exactly why NASA is sending a rover into the Reiner Gamma vortex in 2025 as part of its Lunar Vertex mission.
In just a few years, scientists may have the evidence they need to put this mystery to rest.
The study was published in Journal of Geophysical Research: Planets.