The Silent Travelers: Looking for Alien Robots in Our Own Backyard

Scientists are searching our own solar system for evidence that self-replicating alien machines visited Earth millions of years ago.

Look up at the Moon tonight. It’s been hanging there, essentially unchanged, for billions of years. We’ve studied it, photographed it, walked on it, brought back rocks from it. Alex Ellery, a researcher at Carleton University in Canada, thinks we might have missed something important. Not little green men or flying saucers, but something arguably stranger: the industrial leftovers of alien robots that set up shop there millions of years before humans existed.
The evidence wouldn’t announce itself. No crashed spacecraft with blinking lights. No monuments with alien hieroglyphics. Instead, we’d be looking at chemical signatures in the rocks that don’t quite match what nature produces. Isotope ratios that fall outside the normal range. Industrial waste buried under lunar dust. The kind of anomaly you’d only spot if you knew exactly what you were searching for and had the right instruments to detect it.
Ellery has published an academic paper laying out where these traces might be and what they’d look like. The paper is dense with technical details, but the core argument is straightforward: if advanced civilizations exist elsewhere in the galaxy, they’ve probably sent out robot explorers. Those robots would follow predictable patterns based on physics and resource availability. And some of them might have come here.

Machines That Make More Machines

Mathematician John von Neumann proposed in the 1950s that the most effective way to explore space would be through self-replicating machines Wikipedia. The concept is elegant in its simplicity. You send one robot probe to a distant star system. Instead of just taking pictures and beaming data home, it lands on an asteroid and goes to work. It mines metals. It processes minerals. It builds two copies of itself using those raw materials.
Those two probes fly off to other star systems. Each builds two more copies. Now there are four. Those four become eight. Eight become sixteen. The growth curve goes vertical fast.
Robert Freitas proposed in 1980 that such probes could travel between stars at a slow pace, and when reaching a target system, make copies of themselves using materials like asteroids Uoregon. Each individual probe doesn’t need to be fast. The replication does the heavy lifting. Growth of the number of probes would occur exponentially and the Galaxy could be explored in 4 million years Uoregon.
Four million years sounds like an eternity. For humans, it is. But the Galaxy is over 10 billion years old and any past extraterrestrial civilization could have explored the Galaxy 250 times over Uoregon. Time isn’t the constraint.
Do the math. If any civilization anywhere in the Milky Way developed this technology even just a billion years ago, the probes would have multiplied and spread to every star system long before Earth formed. They should be everywhere. Including here.
That realization leads directly to the most uncomfortable question in astronomy.

The Problem of Silence

The Fermi Paradox at its most basic is, given the high probability that alien life exists out there, why has nobody got in touch yet IFLScience. The physicist Enrico Fermi supposedly asked this during a casual lunch conversation with colleagues in 1950. He’d been thinking about the sheer number of stars in the galaxy, the likelihood that many have planets, the probability that some fraction of those planets develop life. Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy Uoregon.
The numbers all pointed in one direction. We should see evidence of alien civilizations everywhere we look. Radio signals. Massive engineering projects. Probes visiting our solar system.
Instead, there’s silence.
Scientists estimate that alien civilizations in our galaxy could have a median age around 1.7 billion years. That calculation comes from figuring out when the galaxy became safe enough for complex life to survive without getting wiped out. Early on, massive stars exploded in supernovae, and some of those explosions produced gamma ray bursts that would have sterilized any life-bearing planets within thousands of light-years. Those catastrophic events mostly ended about 5 billion years ago, giving the galaxy time to settle down and let civilizations develop.
Consider the timeline. Earth formed 4.5 billion years ago. The first life appeared about 3.8 billion years ago. Humans showed up roughly 300,000 years ago. We’ve had radio technology for barely a century. An alien civilization with even a million-year head start would be so far beyond us technologically that comparing us would be like comparing bacteria to humans. A billion-year head start? We don’t have metaphors adequate for that gulf.
Several explanations have been proposed for the Great Silence. Maybe life itself is incredibly rare, and we’re alone. Maybe life is common but intelligent life almost never evolves. Maybe intelligent species inevitably destroy themselves before they achieve interstellar travel. Maybe the distances are just too vast and interstellar civilizations are effectively isolated from each other, each one alone in their corner of the galaxy.
Or maybe they’re here, and we haven’t recognized the signs.

The Dark Forest Scenario

One explanation for the silence is particularly unsettling. It’s called the Dark Forest hypothesis, borrowed from a science fiction novel that explores the idea seriously. The galaxy is a dark forest. Every civilization is a hunter moving quietly through the trees. You can’t see the other hunters. You don’t know if they’re friendly or hostile. You don’t know how well armed they are. You don’t even know where they are.
The safest strategy is obvious: stay hidden and stay quiet. Don’t broadcast your location. Don’t make noise. Observe everything without revealing yourself.
Any civilization that announces its presence becomes a target. Maybe not immediately, but eventually. Resources are finite. Competition is inevitable. The first civilization to develop overwhelming technological superiority could decide to eliminate potential future competitors before they become threats. Revealing yourself is existentially dangerous.
But you still need information. You need to know what’s out there before it finds you. Self-replicating probes would be perfect for this. Send them out to every star system. Have them observe, gather data, and report back. They multiply and spread silently, watching everything.
Duncan Forgan from the University of St Andrews used mathematical models to explore whether mutated predator probes that cannibalize other probes could reduce the total population Universe Today. His idea tackled a concern some scientists had raised: what if the probes evolve? What if mutations create different varieties, some of which prey on others, and the system collapses into chaos?
Forgan found that the total probe population can stay very high, even with predators present, regardless of assumptions about how hungry the predators were or how the probes moved about the Galaxy Universe Today. Predator-prey relationships don’t end in extinction. They oscillate. Rabbit populations boom, coyote populations boom in response, rabbit populations crash, coyote populations crash, and the cycle repeats. Stability through oscillation.
Carl Sagan and William Newman argued that any civilization advanced enough to make the probes would not be dumb enough to actually make them, and would try to destroy any von Neumann probes found as soon as they were detected IFLScienceWikipedia. Sagan worried about runaway replication. Sagan wrote that implacable replicators will not stop until the entire universe has been converted, which then presumably cannibalize each other IFLScience.
Picture a locust swarm that never stops eating. It consumes every plant, then every animal, then starts consuming itself. That was Sagan’s nightmare scenario for self-replicating machines.
Ellery’s paper pushes back against this fear. Living organisms self-replicate, and they don’t consume everything. Extinctions happen constantly. Evolution produces balance, not apocalypse. You can engineer safeguards into the probes. Error-checking systems to catch and correct mutations. Hard limits on replication cycles, similar to how human cells have built-in limits on how many times they can divide. Build the machines properly and they won’t run amok.
Even if some probes did mutate and start behaving unpredictably, the result wouldn’t be total consumption of the galaxy. It would be an ecosystem. Populations would rise and fall but stabilize over time. There would still be probes out there, lots of them, functioning as designed.
Which brings us back to the central question. If the probes should be everywhere, where are they?

Following the Metal

Ellery’s research suggests that self-replicating probes wouldn’t wander randomly through the galaxy. They’d follow the resources, specifically the heavy elements. You need iron to build structures. Nickel for alloys. Aluminum for lightweight components. Silicon for electronics and glass. Copper for wiring.
Not all parts of the galaxy have equal concentrations of these elements. Scientists call the favorable region the Galactic Habitable Zone. It’s a ring-shaped band roughly 23,000 to 30,000 light-years from the galactic center. Our solar system sits right in the middle of this zone.
Too close to the galactic center and you get problems. The supermassive black hole there spews radiation. Stars are packed densely, increasing the odds of a nearby supernova sterilizing your planet. Too far from the center and you run into a different issue: not enough heavy elements. Stars in the outer regions are metal-poor. They don’t have enough raw materials to form rocky planets or support advanced technology.
The sweet spot formed between 4 and 8 billion years ago, after enough generations of stars had lived and died to seed the galaxy with sufficient heavy elements. This zone contains roughly 12 million stars. About 75% of those stars are older than our Sun by approximately a billion years.
That’s the first important point. Most stars in the habitable zone have a significant head start on us. Any civilizations that emerged there are ancient compared to us.
The second important point is about metallicity. That’s the term astronomers use for the abundance of elements heavier than hydrogen and helium. Life needs certain minimum levels of heavy elements, but manufacturing needs much more. Luckily for hypothetical robot explorers, most stars in the galaxy meet that higher threshold.
Scientists estimate that any star with at least 10% of the Sun’s metallicity would have enough raw materials in its asteroid belts and moons to support extensive mining and manufacturing. That level was reached within the first billion years of the galaxy’s existence. The vast majority of stars in the galaxy’s main disk have met that standard for billions of years.
A wave of self-replicating probes spreading through the galaxy wouldn’t skip many stars. Nearly everywhere they went, they’d find usable resources. They could replicate, build new copies, and keep spreading.

Asteroids Tell No Tales

Bodies with old surfaces such as those of the Moon or Mars might exhibit evidence for collisions from alien probes, but systematic searches have not been conducted up to now ScienceDirectResearchGate.
Ellery’s paper digs deep into the question of whether alien mining operations in the asteroid belt would leave detectable traces. The answer is frustrating: probably not, at least not traces we could easily distinguish from natural processes.
Take metal extraction. There’s a real industrial process called the carbonyl process that’s been used on Earth since the early 1900s. You react metal with carbon monoxide gas. Iron becomes iron carbonyl at 175°C and 100 bars of pressure. Nickel becomes nickel carbonyl at just 55°C and 1 bar. Cobalt becomes cobalt carbonyl at 150°C and 35 bars.
These carbonyl compounds are gases. You can separate them easily since they form at different temperatures. Then you heat them back up and the metals precipitate out in high purity, often exceeding 99%. The carbon monoxide can be recycled. There’s minimal waste.
An alien probe using this process would leave essentially no trace. High-purity metals don’t look artificial. They look like naturally occurring metal deposits that happened to have unusually low impurity levels.
The same problem applies to rock processing. The mineral olivine reacts with water at 200-315°C to produce magnetite, silica, and hydrogen. All three are useful. Magnetite is magnetic, perfect for various applications. Silica makes glass and has a dozen other uses. Hydrogen is fuel. The reaction occurs naturally in certain geological settings, so finding the products wouldn’t prove artificial activity.
You can extract other useful materials through similarly clean processes. The paper walks through the chemistry in detail. The pattern is consistent. Efficient industrial processes that maximize output and minimize waste would produce byproducts that look natural or would produce no byproducts at all.
There’s one exception worth mentioning. If you found porcelain products on an asteroid, that would be definitively artificial. Porcelain requires deliberate processing at high temperatures in controlled conditions. It doesn’t form naturally. But finding a piece of alien porcelain on a random asteroid would require absurd luck. Space is vast. Asteroids are numerous. The odds are essentially zero.
Some scientists have suggested looking for waste dumps from chemical processing. The idea is that even efficient operations might stockpile certain materials that have limited use. The problem is that any civilization capable of building self-replicating space probes would have mastered efficient manufacturing long before. They wouldn’t generate much waste. And even if they did, millions of years of micrometeorite bombardment would have either buried it or scattered it across the asteroid’s surface beyond recognition.
There’s another issue with asteroids as manufacturing sites. Resources are distributed across thousands of different space rocks in different orbits moving at different velocities. Mining them would be like trying to run a steel mill by gathering raw materials from hundreds of different locations scattered across two continents, except everything is moving at thousands of miles per hour relative to everything else and there’s no gravity to help you keep things organized.
You could do it. But there’s a much better option available closer to home.

The Moon as Factory

NASA hosted a Technosignatures Workshop in Houston, Texas in September 2018, and their 70-page report discussed the potential for extraterrestrial probes to have accidentally or intentionally landed on planets or natural satellites in our solar system Time For Disclosure. NASA explicitly states it is even possible that the Earth itself hosts such artifacts Time For Disclosure.
Ellery makes a compelling case that our Moon would be the logical choice for manufacturing operations if alien probes visited our solar system.
The Lunar Reconnaissance Orbiter has mapped the Moon’s surface to 0.5 meter resolution ScienceDirect. That’s detailed enough to spot objects the size of a small car. Although there is only a tiny probability that alien technology would have left traces on the moon in the form of an artifact or surface modification of lunar features, this location has the virtue of being close and of preserving traces for an immense duration ScienceDirect.
The Moon has gravity. Not much, just one-sixth of Earth’s, but that’s enough to keep materials from floating away during processing. It makes handling solids and liquids manageable instead of nightmarishly difficult like it would be in the zero gravity of an asteroid.
The Moon is stable. It’s been orbiting Earth in essentially the same configuration for over 4 billion years. It has no atmosphere, no weather, no plate tectonics, no volcanic activity to speak of. Build something on the Moon and it stays put essentially forever unless a meteorite hits it directly.
The Moon also offers an excellent selection of raw materials. The bright highland regions you see through a telescope are rich in a mineral called anorthite. That mineral contains aluminum, silicon, calcium, and oxygen. The dark regions called maria (Latin for “seas,” though they’re actually ancient lava plains) contain a mineral called ilmenite with iron, titanium, and oxygen.
Aluminum deserves special mention because of how versatile it is. It’s lightweight but strong enough for structures. Alloyed with silicon, it becomes hard enough for tools. It conducts electricity well, so it works for wiring. It reflects heat efficiently, making it good for thermal management. It’s highly reflective, so you can make mirrors and solar concentrators from it. The oxide form, alumina, is nearly as hard as diamond and works as an industrial abrasive. One element, dozens of critical applications.
The paper describes what it calls a lunar industrial ecology. The concept is a closed-loop system where waste from one process becomes feedstock for another. You extract aluminum from highland rocks using one set of chemical reactions. The byproducts from those reactions are inputs for extracting silicon. The byproducts from that become inputs for the next process. Very little gets discarded because everything is valuable for something.
To supplement what the Moon provides naturally, you could use electromagnetic catapults called mass drivers to soft-land asteroids on the lunar surface. This solves the problem of accessing materials the Moon lacks, particularly certain metals like nickel, cobalt, and tungsten that are common in asteroids but rare on the Moon.
The paper goes into significant detail about specific chemical processes, temperatures, pressures, and reaction sequences. The technical complexity is real, but the key point is simpler: all of these processes use relatively straightforward chemistry and materials that are common in space. An advanced civilization could build a sophisticated, self-sufficient industrial base using nothing but lunar rocks, ice from permanently shadowed craters, and supplemental metals from captured asteroids.
If alien probes did exactly this millions of years ago, what evidence would remain today?

Atomic Fingerprints

Long-term manufacturing operations on the Moon would require reliable, continuous power. Lots of it. Nuclear fission reactors would be the obvious choice.
Solar power works during the lunar day, but the Moon’s day-night cycle lasts 28 Earth days. That means 14 consecutive days of sunlight followed by 14 consecutive days of darkness. You’d need enormous battery banks to store power through the two-week nights. Nuclear reactors eliminate that problem by generating power continuously regardless of whether the Sun is up or down.
The Moon has uranium and thorium scattered through its rocks at low concentrations. Uranium averages about 0.3 parts per million. Thorium averages 1 to 2 parts per million. Those sound like tiny amounts, and they are, but they’re enough.
There’s a region on the Moon’s near side called Oceanus Procellarum where thorium concentrations reach 7 parts per million. One particular spot, Compton-Belkovich, has 9 parts per million. Scientists have mapped these concentrations using gamma-ray spectrometers on lunar orbiters that can detect the characteristic radiation from radioactive decay.
Thorium-232 is nearly perfect as nuclear fuel for our purposes. It has a half-life of 14 billion years, so virtually all the thorium that existed when the solar system formed is still around. When you expose thorium-232 to neutrons in a reactor, it undergoes a series of transformations and becomes uranium-233, which is fissile. That means it can sustain a nuclear chain reaction.
The British built a series of reactors in the 1950s and 60s called Magnox reactors that used natural uranium without any enrichment. Enrichment is the difficult, expensive process of separating uranium isotopes to increase the concentration of uranium-235. Magnox reactors skipped that step entirely by using natural uranium and surrounding it with graphite to slow down the neutrons, making the chain reaction possible.
You could build essentially the same design using lunar materials and thorium-232 instead of uranium-235. The fuel rods would be clad in a magnesium-aluminum alloy. The neutron moderator would be graphite blocks. The coolant would be carbon dioxide gas.
All of these materials can be extracted from lunar rocks and carbonaceous asteroids. Magnesium comes from a lunar mineral called forsterite through a series of chemical treatments. Aluminum comes from anorthite, abundant in the highlands. Carbon comes from asteroids. You heat the organic compounds and they release carbon dioxide and other volatiles. Iron comes from ilmenite through a simple hydrogen reduction reaction. Nickel comes from metallic meteorites that have fallen on the Moon over billions of years.
You could, in principle, build the entire reactor from scratch using only materials available on or near the Moon. No Earth-supplied components required.
When you run a nuclear reactor burning thorium-232, the fission process produces specific isotopes as waste products. Two notable ones are neodymium-144 and barium-137. These isotopes wouldn’t exist in high concentrations naturally. They’re signatures of nuclear fission.
We actually have an example of a natural nuclear reactor on Earth. In 1972, French scientists analyzing uranium ore from Oklo, Gabon discovered that the uranium isotope ratios were wrong. There was too little uranium-235 compared to uranium-238, indicating that some of the uranium-235 had been consumed in fission reactions. There was also an excess of thorium-232. Further investigation revealed that about 1.8 billion years ago, uranium ore had been concentrated by groundwater to the point where it reached critical mass and sustained a natural nuclear chain reaction for thousands or even millions of years.
Scientists discovered the Oklo reactor because the isotope ratios were anomalous. The same principle would apply to ancient artificial reactors on the Moon. If alien probes ran nuclear reactors there millions of years ago, we would find anomalous ratios of thorium-232 to neodymium-144, or thorium-232 to barium-137. These ratios would deviate significantly from what natural decay produces.
Detecting these anomalies would require landing spacecraft on the Moon, collecting samples from promising locations, and analyzing them with sensitive mass spectrometers. We can’t do this from orbit. But it’s within our current technological capability. The measurements aren’t science fiction. They’re just expensive and require going to specific locations on the lunar surface.
The paper calculates the scale of operations we’re talking about. To seriously industrialize the Moon, you’d need roughly 1.5 million factory modules, each one producing materials and building new modules. Each module would require about 2 megawatts of electrical power. Total power generation: 3 terawatts.
That’s approximately equal to human civilization’s current global electricity consumption. The isotopic signature from that much nuclear power generation over years or decades would be spread widely across the lunar surface, particularly concentrated in regions with the highest thorium deposits. We’d have a reasonable chance of detecting it even with limited sampling campaigns.
A reactor running for decades or centuries would leave a clear mark. The signature wouldn’t fade quickly. Radioactive isotopes with half-lives of thousands or millions of years would still be detectable today even if the reactors shut down millions of years ago.

Economics, Trade, and Gifts

Ellery’s paper takes an interesting turn into economics and game theory. These topics might seem out of place in a discussion about robot space probes, but they’re actually fundamental. Economics is really just the rational distribution of scarce resources to achieve goals, and that principle is universal. It applies to any intelligent system, whether biological or artificial, whether alien or human.
Research on primates has shown that even non-human animals understand concepts like fairness and reciprocity. Capuchin monkeys react negatively when they receive unequal rewards for equal work. Give one monkey a grape for completing a task and the other monkey a cucumber slice for the same task, and the cucumber-recipient gets upset. They understand they’re being treated unfairly. Chimpanzees will actively work to equalize reward distribution when they notice inequality.
This isn’t cultural. It’s evolved. Fairness and reciprocity are biological adaptations that emerged because they’re useful for survival in social groups. Game theory explains why. The optimal long-term strategy in repeated interactions is tit-for-tat: start by cooperating, then mirror what the other party does. If they cooperate, continue cooperating. If they defect, punish them but give them opportunities to return to cooperation. This strategy outperforms pure cooperation (which gets exploited) and pure defection (which leads to endless conflict).
Now apply this to alien probes arriving at our solar system. The probes need resources. They’re going to take some. But what if there’s an intelligent species already living here? The probes have several options. They could try to hide and take resources stealthily. They could use force to take what they need. Or they could negotiate a trade.
Trade is the most stable long-term strategy. It establishes a cooperative relationship that both parties benefit from. The probes get the resources they need. The resident species gets something valuable in return.
So imagine a self-replicating probe landing on the Moon while intelligent life is developing on Earth below. These humans aren’t spacefaring yet, but they show potential. What should the probe do?
One option: take the needed resources and leave something valuable in exchange. Scientific information. Maps of the galaxy. Technical blueprints. Or most valuably, a complete copy of itself—a universal constructor that can build anything, including copies of itself.
This would be the ultimate gift. It’s like giving someone a 3D printer that can print copies of itself, along with the feedstock to get started and the instruction manual for how to use it. With that technology, the recipient civilization could industrialize their solar system exponentially and potentially join the community of spacefaring civilizations.
But there’s a critical constraint. The gift needs to be hidden where only a civilization at a certain technological threshold can find it. Giving advanced technology to a primitive civilization that can’t understand or use it responsibly is pointless at best and potentially harmful. The gift needs to remain hidden until the discovering civilization demonstrates the capability to use it safely.

The Perfect Hiding Spot

Among missions outlined by researchers, there are proposals to search for evidence of impact sites or other artifacts that might be present on the Moon, which might have resulted from intelligent probes or other extraterrestrial flotsam and jetsam that might have made its way there over the course of the last several millions or even billions of years The Debrief.
Ellery suggests that the ideal location for hiding such a gift would be in association with metallic asteroid deposits buried beneath the lunar surface. The logic is elegant.
The Moon has been hit by asteroids throughout its history. Small ones make small craters. Large ones make enormous impact basins. Sometimes a large metallic asteroid made primarily of iron and nickel slams into the Moon at a shallow angle. Instead of vaporizing completely on impact, chunks of the asteroid survive and get buried under ejected lunar material.
These buried metal deposits are valuable. When humans start seriously mining the Moon, we’ll specifically target these areas because they contain concentrated sources of iron, nickel, cobalt, and other metals essential for industry. Getting metals from these deposits would be easier than extracting them from lunar rocks where they’re dispersed at low concentrations.
Finding these deposits requires sophisticated prospecting. You look for magnetic anomalies because iron and nickel are ferromagnetic. You look for unusual elemental signatures in the rocks using spectrometers. You drill exploratory holes and analyze core samples. All of this requires significant technological infrastructure.
The South Pole-Aitken basin is particularly intriguing. It’s an enormous impact crater on the Moon’s far side, measuring about 1,600 miles across and 8 miles deep. It formed approximately 4.3 billion years ago when something absolutely massive hit the Moon. Orbital studies suggest there are iron-rich deposits there from the impactor or from subsequent asteroid strikes in the region.
Some areas within South Pole-Aitken show weak magnetic anomalies around 10 nanoteslas in strength. That’s ten billionths of a tesla, incredibly faint but detectable with sensitive magnetometers. These anomalies suggest buried metallic material beneath the surface.
Spacecraft with infrared and gamma-ray sensors have attempted to detect metallic iron in the top few inches of regolith at South Pole-Aitken. Results have been ambiguous. The instruments couldn’t detect metallic iron within the top 10 centimeters.
But absence of evidence in the top 10 centimeters isn’t evidence of absence deeper down. South Pole-Aitken formed 4.3 billion years ago. Over that immense timescale, countless small meteorites have peppered the surface. Each impact pulverizes rock, mixes the soil, and buries older material under fresh ejecta. This process, called impact gardening, operates continuously at a slow pace. After billions of years, it would have buried any ancient surface features under meters of well-mixed regolith.
If you wanted to hide something on the Moon and ensure it remained hidden until a civilization reached a specific capability threshold, burying it 10 to 100 meters deep in association with asteroid metal deposits would be perfect. From orbit, the deposits would look completely natural. You’d only find the hidden artifact once you started actual mining operations in the area.
Access would require serious infrastructure. Excavators to remove overburden. Drilling equipment to reach depth. Processing facilities to separate metals from rock. Power systems to run all the equipment. Either human crews with life support systems or very sophisticated autonomous robots. Communication networks. Supply chains.
By the time you had all that infrastructure in place and working, you’d have proven you could handle the technology you were about to discover. The gift would reveal itself at precisely the moment you’d earned the right to receive it.
Ellery calls this the Vygotsky hypothesis, named after the psychologist who studied how tool use and cognitive development are interconnected. The hypothesis is straightforward: mastering self-replication technology on the Moon demonstrates you’re ready for interstellar technology. The skills required overlap almost completely. Advanced manufacturing. Artificial intelligence. Closed-loop resource recycling. Long-term reliability. Systems integration. If you can build self-replicating lunar factories, you can build interstellar probes. If you can’t, you’re not ready for the gift.

Teaching Computers to See

Dr. Jacob Haqq-Misra, one of the leading figures in the scientific search for alien technosignatures, said that we cannot necessarily rule out the possibility of artifacts on the moon until we search The Debrief.
At the direction of the United States Congress, NASA opened up funding opportunities for technosignature research a few years ago, and one of the first grants related to nonradio technosignatures went to Haqq-Misra’s collaboration The Planetary Society.
The Moon’s surface covers about 14.6 million square miles. That’s roughly the combined area of North and South America. Even with high-resolution orbital photographs showing details down to half a meter, manually examining every square meter would take enormous teams decades to complete. Nobody has that kind of time or budget.
Artificial intelligence offers a solution. Researchers have developed machine learning systems that can automatically scan images looking for anomalies—things that deviate from expected patterns.
The basic approach trains an AI system by feeding it thousands of images of normal lunar surface. Craters of various sizes. Boulder fields. Slopes and valleys. The system learns what typical lunar terrain looks like, building an internal model of normal patterns, textures, shapes, and structures.
Then you feed the trained system new images and ask it to flag anything unusual. The system compares what it sees to its learned model of normal and highlights anything that doesn’t fit. Some flagged items will be unusual natural features. Some might be artifacts.
Researchers have tested these systems on Lunar Reconnaissance Orbiter images with known human artifacts. They fed the AI photos of Apollo landing sites including the lunar modules, rovers, and equipment we left behind. The AI correctly identified these human-made objects as anomalous, distinguishing them from the natural background.
Four different AI approaches all worked successfully: variational autoencoders, kernel density estimation, isolation forest, and farpoint algorithms. The technical implementation details differ, but they all achieved the same goal of spotting artificial objects on natural terrain.
SETA researchers hope to check whether any artificial structures larger than 10 meters exist on any solid surfaces within the Solar System, and to search thoroughly for any waste heat that might be emitted by technological artifacts on these worlds The Planetary Society.
Ten meters is about the size of a school bus. That’s the current practical detection threshold. Anything smaller becomes difficult to distinguish reliably from natural features even with our best cameras.
There’s a fundamental limitation to orbital searches. We’ve mapped the surfaces of various moons and planets at high resolution, but we’ve barely scratched beneath the surface. The Earth and Moon have been photographed thoroughly enough that we can be confident no school-bus-sized alien artifacts are sitting exposed on the surface in plain view. We would have noticed them by now.
But that doesn’t rule out buried artifacts. Our subsurface exploration of the Moon consists of a few meters of drilling at six Apollo sites and a couple of Soviet robotic sample return missions. That’s negligible compared to the Moon’s total volume. There could be entire buried facilities that we simply haven’t encountered yet because we haven’t dug in the right places.

Questions Without Answers Yet

Ellery’s paper acknowledges its limitations openly. The analysis focuses primarily on the inner solar system—Mercury, Venus, Earth, Mars, the Moon, and the asteroid belt. This perspective is somewhat human-centered. We’re familiar with this region. We’ve sent probes there. We understand the resources and conditions.
But as the British scientist J.B.S. Haldane observed, the universe is not only stranger than we imagine, it’s stranger than we can imagine. An alien civilization might approach exploration completely differently than we would. They might prefer the outer solar system for reasons we haven’t considered. They might use technologies we haven’t thought of. They might follow logic that seems bizarre to us.
The moons of Jupiter and Saturn offer their own advantages. Some have liquid water oceans beneath ice shells. Some have organic compounds that could serve as feedstock for industrial chemistry. The outer solar system is cold, which is actually beneficial for certain kinds of manufacturing and computing that generate heat. There are arguments for focusing on the outer solar system instead of the inner one.
Still, the paper makes a case worth considering seriously. If self-replicating probes visited our solar system, they would have left traces we could potentially detect with current or near-future technology. The traces wouldn’t be obvious. No abandoned bases with fusion reactors still running. No monoliths with alien writing. Nothing that dramatic.
Instead, we’d be looking for subtle chemical signatures. Isotope ratios that fall outside natural ranges. Perhaps buried structures or equipment waiting to be discovered by mining operations. The signatures would be there if we knew where to look and what to measure.
We’re going to the Moon anyway. Multiple nations are planning permanent lunar bases over the next few decades. Private companies are developing technologies for lunar mining. We’ll be excavating, prospecting, drilling, analyzing samples, and studying the Moon in unprecedented detail.
Consider a historical parallel. The Chicxulub crater in Mexico, the impact that killed the dinosaurs 66 million years ago, was discovered in the 1970s by petroleum geologists. They were looking for oil deposits using subsurface surveys. They found something far more significant—evidence of a catastrophic asteroid impact that reshaped the planet’s biology. They weren’t looking for evidence of mass extinction, but they recognized the anomaly when they saw it.
The same could happen on the Moon. Mining engineers and geologists will be searching for economically valuable deposits. If they encounter anomalous isotope ratios or unusual structures buried in the regolith, they’ll notice. Scientists are trained to spot anomalies. Even if they’re not specifically looking for alien artifacts, they’ll recognize when something doesn’t fit natural patterns.
This isn’t about believing in flying saucers or conspiracy theories. It’s about following logic. Self-replicating probes are a rational way to explore the galaxy. Physics and chemistry are universal. Economic principles are universal. The mathematics of resource extraction and industrial efficiency work the same everywhere.
If we were to send self-replicating probes into the galaxy—and serious researchers are discussing exactly that—they would behave in certain predictable ways. They’d seek raw materials in asteroids and moons. They’d establish bases where gravity helps with operations. They’d use available energy sources efficiently. They’d minimize waste. They’d leave chemical signatures of their industrial processes.
The logic applies equally whether the probes are human-made or alien-made. Physics doesn’t care about the origin of the engineer. A nuclear reactor burning thorium-232 produces the same fission products regardless of whether humans or aliens built it.
So the question isn’t whether such signatures could exist in principle. The question is whether we’re looking carefully enough to find them if they’re actually there.
The probes might be silent now. Their builders might have gone extinct billions of years ago or moved on to other galaxies. But the machines they left behind might still be here, dormant in the asteroid belt or buried beneath lunar regolith, waiting for the next intelligent species to find them.
Or maybe they’re still active, watching us from hiding, measuring our technological progress against some predetermined criteria, waiting to make contact when we cross a specific threshold. Patient beyond human comprehension, content to wait millions of years for the next species to evolve and discover them.
Or perhaps they’re just ruins. Ancient factories that ran out of fuel millions of years ago. Broken machinery slowly being buried by micrometeorite impacts. Archaeological sites waiting to be excavated like Egyptian pyramids or Roman aqueducts—monuments to a civilization we’ll never meet, built for purposes we can only guess at.
The search is accelerating. AI systems are improving at spotting anomalies in images. Our maps of the Moon are getting more detailed every year. Mining operations will begin within the next decade or two. Sample return missions are planned.
Within our lifetimes, we might answer one of the deepest questions humans have ever asked: are we alone, or have others been here before, leaving their marks for us to find?
The watchers may be silent. The traces they left might be subtle. But if they’re there, we’re finally developing the tools and the motivation to discover them.
And if we don’t find anything? That’s an answer too. It would tell us something important about how rare technological civilizations are, or how short-lived they tend to be, or how different their priorities might be from what we assume.
Either way, the search is worth conducting. The question is too important to leave unanswered.

References

NOTE: Some of this content may have been created with assistance from AI tools, but it has been reviewed, edited, narrated, produced, and approved by Darren Marlar, creator and host of Weird Darkness — who, despite popular conspiracy theories, is NOT an AI voice.