For centuries, the surface of the moon has hid a mystery: bright, twisting swirls that stretch across thousands of square miles of the lunar landscape, visible to telescopes on Earth but defying explanation. Now, at last, scientists are beginning to understand them — and it turns out they’re stranger than anyone imagined. These mysterious “moon swirls” are the result of ancient underground force fields that protect the moon from the barrage of subatomic particles spewed out by the sun. Each swirl is a twisting blanket of pristine rock intertwined with darkened, radiation-exposed material.
While most features on the moon are sharp and rough, lunar swirls are instead smooth and wispy, like cirrus clouds painted on the surface. They are also widespread; some appear in Mare Marginis (Latin for “edge sea,” because from Earth it appears on the easternmost edge of the moon’s face), while another, Gamma Reiner, is thousands of kilometers to the west. They can be seen in both the smooth, dark mariae (Latin for “seas,” which they vaguely resemble to the naked eye on Earth) and the heavily cratered highlands, suggesting that they are not associated with any particular feature. Because they are brighter than the mariae—which are plains of dark, flooded basaltic lava—lunar swirls are easier to spot in these regions.
Observers have long realized that these swirls don't cast shadows, so they can't be topographic features like hills or valleys. Instead, they resemble what you'd get if clouds collapsed onto the surface, though without a noticeable atmosphere this is impossible on the moon. And even if such a “cloud collapse” were possible there, more recent observations of lunar vortices show that they are made of the same stuff as their surroundings – they No superimposed matter, but rather part of a pre-existing surface.
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Gamma Reiner is one of the largest and best-studied lunar vortices; a flattened oval, like a staring eye, more than 100 kilometers wide, with two long, thin tails extending hundreds of kilometers at either end. This makes it large enough to be visible even in small telescopes, and I actually saw it with my own eyes! At that time I was amazed that such a beautiful and noticeable feature could still defy explanation.
A photograph showing Reiner Gamma, a “lunar spiral” near the right edge of the Moon. It was taken using a 20-centimeter telescope and a phone camera.
It turns out that the striking brightness of the moon's spirals is a crucial clue to what they are and where they came from. Material on the surface darkens over time as it is hit by radiation from the sun. A rule of thumb is that anything brighter on the moon is younger. For example, look at the shiny, feathery “rays” of relatively fresh material that are splashed around giant craters like Quietwhich formed about 100 million years ago. That's practically yesterday in lunar terms, because the surface of the Moon is billions of years old and essentially static compared to the surface of the Earth!
During the Apollo era, scientists speculated that the vortices might be material ejected by recent volcanism. But maps of the moon's magnetic field (made using data from Apollo 15 And 16) showed that all the swirls coincided with regions of slightly stronger magnetism, indicating a different and more complex origin. Understanding how this relates to their brightness requires a quick look back at the history of the Moon and geophysics of magnetic fields.
Unlike Earth, the Moon today has no global magnetic field. It was weak billions of years ago when it was still molten, but it quickly faded as the Moon cooled. However, as rocks solidified on the surface, they were able to retain some of this ephemeral magnetism, creating more stable, localized regions with slightly stronger magnetic fields. Given their ancient origins, these are called “relic” fields, and many are associated with lunar swirls.
The real reason for this connection became clear about ten years ago, when scientists published their results in The Nature of Communication which showed that the relic fields around the vortices, no matter how weak, can still be strong enough to slightly deflect the solar wind falling on the lunar surface. This wind consists of subatomic particles from the sun, and the trajectories of electrically charged particles such as electrons and protons can be altered by magnetic fields. Where the CMB fields are strongest, the particles are deflected, darkening the ground they fall on and leaving curious swirls on the cleaner, magnetically shielded surface.
So it's surprising that the lunar rule of “brighter” means “younger” isn't always true. Sometimes “brighter” means something has escaped the aging effects of cosmic radiation.
I remember reading this research paper with great pleasure and the smile on my face grew wider and wider. Star Trek My inner fan was overjoyed: lunar vortices exist because our Moon deflector shields—force fields!
Now you may be wondering: Sure, the swirls are magnetic. But why are they long and twisty? In 2018, additional research showed that the source of the magnetic fields that create the vortices must be shallowless than three kilometers below the surface. This suggests that the eddies trace hidden geological features formed by ancient lunar volcanism: lava tubes, grooves, and dikes. Ribs are long, shallow gullies cut by flowing lava. Sometimes, as the flowing lava cools, it forms a hard rock top, creating a subsurface lava tube. Some eddies are found near lava tubes: Mare Ingenii (Sea of Intelligence) has eddies and Pits on the surface indicating the presence of lava tubes underneathDykes are geological formations where magma intrudes and cools between existing layers of rock, creating huge sheet-like structures.
If the rock in such structures has a relic magnetic field, it can create swirls on the surface. In 2024, a group of scientists published an article in Journal of Geophysical Research: Planets This shows that deposits of ilmenite, a mineral common in lunar magma, can increase the local abundance of elements such as iron and nickel in dikes, boosting the levels of magnetism there.
While this paints a good overall picture of the vortices and how they formed, there are of course unanswered questions. Another paper published in Journal of Planetary Science indicates that there is is some topographic variations in eddies; on average, the brighter regions of the swirls tend to be a few meters lower in altitude than the darker regions. It is not yet clear why this might be, and in their paper, the scientists note that the ultimate source of the bleaching has not been finally Definitely. While the solar wind remains a strong candidate, other models suggest that differential coloration arises from material scattered by comets, or statically charged dust particles kicked up by tiny micrometeorite impacts that are then sorted by the Moon's relic magnetic fields.
To me, the real message of the complex origin story of the moon’s spirals is simple: The moon is literally the closest celestial object to Earth in the entire universe, but there’s still so much we don’t understand. That’s cause for excitement, not dismay. As we explore the moon more closely — perhaps even personally, building on our first forays there more than half a century ago — we’ll have a chance to unravel more of its mysteries, including some that are baffling us right before our eyes.