For centuries, the surface of the Moon has harbored a mystery: bright, sinuous spirals that cover thousands of square kilometers of the lunar surface, visible but unexplained by telescopes on Earth. Now, scientists are finally beginning to unravel the mystery, and it turns out to be stranger than anyone could have imagined. These enigmatic “Moon spirals” are the result of an ancient underground force field that protects the Moon from a barrage of subatomic particles blasting from the Sun. Each spiral is a twisted blanket of pure rock, tangled with irradiated, blackened material.
While most of the Moon’s surface features are jagged and rugged, the Moon’s spirals are smooth and faint, like cirrus clouds painted on the surface. The spirals are widespread, with some appearing in Mare Marginis (Latin for “edge sea” because it is the eastern edge of the Moon’s surface as seen from Earth) and others in Reiner Gamma, thousands of kilometers to the west. The spirals are seen both in the smooth, dark lowlands of maria (Latin for “ocean”; vaguely resembling a sea when seen with the naked eye from Earth) and in the heavily cratered highlands, suggesting that they are not associated with any particular feature. The spirals are brighter than the maria (plains of dark, flooded basaltic lava), making it easier to spot the Moon’s spirals in those areas.
Observers have long known that the spirals aren’t hill- or valley-like features because they don’t cast shadows. Rather, they look like clouds collapsing onto the surface. This is impossible, however, since the Moon has no significant atmosphere. And even if such “cloud collapses” could occur on the Moon, recent observations of lunar spirals suggest that they are made of the same material as their surroundings; that is, they are made of a material that is not viscous, like a cloud that has collapsed onto the surface. do not have It is not a covered substance, but rather part of the existing surface.
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Rainer Gamma is one of the largest and best studied of the lunar spirals. It is a flattened oval like a staring eye, over 100 kilometers wide, with two long, thin tails stretching out for hundreds of kilometers from each end. This makes it large enough to be seen in a small telescope, and I have seen it in my own. At the time, I was amazed that such a beautiful and striking feature remains unexplained.
Photograph showing Rainer Gamma, a “Moon Vortex” near the right edge of the Moon. Taken using a 20 cm telescope and a cell phone camera.
The remarkable brightness of the Moon’s spirals turns out to be an important clue that explains what they are and where they came from. Surface material gets darker over time as it is bathed in radiation from the Sun. As a rule of thumb, the brighter something is on the Moon, the younger it is. Look, for example, at the glowing, feathery “rays” of relatively new material that spatter around giant craters such as Tycho, which formed about 100 million years ago. This is practically yesterday from the Moon’s perspective, because the Moon’s surface is billions of years old and essentially stationary compared to Earth’s surface.
During the Apollo era, scientists speculated that the swirls were material ejected by recent volcanic activity. However, maps of the Moon’s magnetic field ( Apollo 15 and 16) show that the spirals are all aligned with regions of slightly stronger magnetism, suggesting a different, more complex origin. To understand how this relates to its brightness, we need to briefly look at the history of the Moon and the geophysics of its magnetic field.
Unlike Earth, the Moon currently has no global magnetic field. It had a weak magnetic field billions of years ago when it was still molten, but this weakened rapidly as the Moon cooled. But as the rocks on its surface solidified, they were able to retain some of their temporary magnetism, forming localized areas with slightly stronger, more permanent magnetic fields. These are called “relic” fields because of their ancient origin, and many are associated with lunar spirals.
The real reason for this link became clear when scientists published their findings about 10 years ago. Nature Communications The study showed that the residual magnetic field around the spirals, while weak, is strong enough to slightly deflect the solar wind hitting the Moon’s surface. This wind is made up of subatomic particles from the Sun, and the magnetic field changes the trajectories of electrically charged particles like electrons and protons. Where the residual field is strong, the particles are deflected to the side, darkening the ground they fall on and leaving strange swirling patterns on the cleaner, magnetically shielded surface.
Surprisingly, the rule of thumb for the Moon that bright means young doesn’t always hold true. Sometimes bright means it has avoided the aging effects of cosmic radiation.
I remember reading the research paper with delight and having a smile on my face. Star Trek The fan in me was thrilled. The moon swirls were a reminder that our moon is Deflector Shield—Force field!
The question is, if the whirlpools are indeed magnetic in nature, why are they so long and winding? Further research in 2018 showed that the source of the magnetic field that creates the whirlpools must be shallow, i.e. less than 3 kilometers below the surface. This suggests that the whirlpools trace buried geological features formed by ancient lunar volcanic activity: lava tubes, rills, and dikes. Rills are long, shallow grooves carved by flowing lava. As the flowing lava cools, a solid rock roof forms over it, and sometimes lava tubes form underground. Some whirlpools have been found near lava tubes. For example, the surface of Mare Ingénie, which means “Sea of Wisdom,” has swirls and holes that indicate lava tubes beneath it. Dikes are geological features where magma intrudes between existing rock layers and cools to form huge sheet-like structures.
If rocks with such structures have residual magnetic fields, they could generate vortices on the surface, a team of scientists reported in a paper published in 2024. Journal of Geophysical Research: Planets They suggest that deposits of ilmenite, a mineral common in lunar magma, could increase the local abundance of elements such as iron and nickel in the dikes, amplifying the amount of magnetism in the area.
This paints a good overall picture of whirlpools and how they form, but of course there are still unanswered questions. Planetary Science Journal There teeth The spirals have topographical variations, and on average, the lighter parts of the spiral tend to be at a few meters lower elevation than the darker parts. It’s not yet clear why this is the case, but the scientists note in the paper that the underlying causes of the discoloration are still unknown. Decisively Although the solar wind remains the leading candidate, other models propose that the difference in colour could be due to material scattered by comets, or electrostatically charged dust particles kicked up by micrometeorite impacts, either of which are then sorted by the Moon’s residual magnetic field.
To me, the real message of the Moon’s complicated origin story is quite simple: the Moon is literally the closest object to Earth in the entire universe, yet there is still much we don’t understand about it. That’s a reason for excitement, not discouragement. Building on our first visit to the Moon over half a century ago, as we explore it in more detail, perhaps even visit it ourselves, we will have the opportunity to solve more of its mysteries, including some that perplex us.
