Could the clues to ancient alien civilizations be hiding in moon dust?

Most of our experience with the Search for Extraterrestrial Intelligence (SETI) has focused on capturing radio signals that alien species have sent out, whether intentionally or unintentionally. That creates a huge “synchronicity” problem—what if there aren’t any alien civilizations broadcasting radio signals now, but there were a billion years ago? The Milky Way is around 13 billion years old—hoping that we exist at the same time as an alien civilization that happens to be actively messaging is a huge leap of faith.

But according to a new paper available as a preprint on arXiv and submitted to the International Journal of Astrobiology by Lewis J. Pinault, an associate researcher at the SETI Institute, and his co-authors, we could take a completely different approach to trying to find alien civilizations—by looking for evidence of them in lunar dirt.

That idea is not as crazy as it sounds. To be clear, it doesn’t mean that aliens once lived on the moon—or anywhere in the solar system, for that matter. But the moon is a really, really good garbage collector. The idea proposed in the paper is that, instead of looking for simple radio waves, we should look for physical artifacts that could only have been created by intelligent aliens, and the moon is a great place to look for them.

Firstly, what does “artifacts” in this case actually mean? The paper discusses two different types of particles. One is an Arkhipov particle, named after Ukrainian astronomer Alexei Arkhipov, who first floated this idea in the 1990s. These are tiny pieces of unintentional industrial debris. If an alien civilization decides to build a Dyson swarm, some parts of it will inevitably be destroyed over time.

Fragments from that destruction could be pushed out of the star system that hosted that megastructure, and they could eventually make their way to our own solar system. This isn’t as far-fetched as it sounds, as the sun rotates all the way around the Milky Way once every approximately 230 million years—and the Milky Way itself is around 13 billion years old. So our own solar system has already traveled through much of the galaxy repeatedly.

The second type of particle is known as a Bracewell particle, named after physicist Ronald Bracewell. These are intentionally sent to other solar systems—essentially, they act as “smart dust.” And they might very well have ended up on the moon at some point over the last 13 billion years or so.

But why the moon? Earth is a much bigger target, right? The moon has several advantages in terms of preservation that Earth doesn’t.

First, it doesn’t have an atmosphere, so particles aren’t vaporized before they even hit the surface. Second, it doesn’t have plate tectonics or a water cycle, so any particles that do hit the surface aren’t immediately trapped under a mountain or washed away into an ocean. And third, it experiences “impact gardening,” whereby pieces of micrometeoroids hit the surface and churn the top layer of soil. This allows microscopic pieces of technology to become buried under up to a few meters of regolith, protecting them from cosmic rays that might otherwise destroy them.

The journey to the moon itself is dangerous, though. As these technological materials travel through space, they’re subjected to cosmic rays and particles of dust shooting through interstellar space alongside them in a giant cosmic shooting gallery.

However, the paper notes that grains made of “refractory material,” such as advanced ceramics, graphene or titanium-tungsten superalloys, can hold up against the onslaught for anywhere from 100 million to 1 billion years.

Even if they do, they still have to survive entry into the solar system itself. They would pick up speed as they got caught by the sun’s gravitational pull, eventually hitting a relative velocity of 42 km/s (26 miles per second) upon reaching 1 AU—the average distance of Earth from the sun. Hitting the moon’s surface at any speed over 5 km/s (3 miles per second) results in certain vaporization, though, so the particles would have to slow down in advance.

According to the paper, radiation pressure from the sun itself might be enough to do that for grains of a specific size and density. Instead of continuing to accelerate inward toward the sun, the particles are slowed to a speed at which, when they eventually impact the lunar surface, they will still be recognizable.

What form those “recognizable” chunks would take is still debated, though. They could be micrometer-sized grains of advanced materials, or they could potentially get caught in agglutinates, the tiny glassy droplets of material created during the flash-melting events caused by impact gardening.

No matter what their form, finding these technological materials would make looking for a needle in a haystack look easy. The authors note that searching through 1 cubic meter of lunar regolith, which equates to 1.5 metric tons of dirt, would require searching more than a trillion micrometer-sized grains. There’s no way a manual process can effectively do that.

Their solution, unsurprisingly, is to turn to AI. Running the regolith through a high-resolution scanning electron microscope could feed images directly into a computer vision model, including one called YOLO-ET, which the research team used in previous papers. Any aberrant particles could be automatically flagged for closer inspection, which could include time at a focused ion beam (FIB) facility or being subjected to nano-CT scanners.

Even if these experiments result in nothing—or a “null value,” as scientists like to say—that still provides valuable statistical information. Calculations show that if we don’t find any hint of technology in 1 cubic meter of lunar soil, that rules out scenarios in which sunlike stars in the Milky Way have dispersed more than 0.1 Earth masses of artificial dust over the entire history of the galaxy.

That may sound like a lot, but when you’re talking about potential Kardashev Level II civilizations, 10% of Earth’s mass is only a fraction of what they’re working with.

Also, a null result in 1 cubic meter of regolith means no civilization was intentionally sending out probes at a rate of more than 0.4 kg per billion years. That might not sound like much—and admittedly, in this case it isn’t—but at least it’s a starting point to put some constraints on the potential existence of advanced alien civilizations.

Given the huge impact finding even one such civilization would have, it’s not likely we’ll stop looking anytime soon. And as the moon becomes more and more of a focal point of our space exploration efforts, maybe someone will take the time to sift through a literal ton of dirt to find evidence that might answer one of humanity’s longest-standing questions: Are we alone?

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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