The idea sounds like science fiction, yet a Canadian researcher believes it deserves serious attention. Professor Alex Ellery of Carleton University suggests that self-replicating probes from other worlds could already exist within our Solar System, possibly hidden in plain sight. His recent paper, available as a preprint on arXiv, urges the Search for Extraterrestrial Intelligence (SETI) to look for their signs.
What Are Von Neumann Probes?
In 1949, mathematician and physicist John von Neumann first proposed the idea of a “universal constructor” – a machine capable of building copies of itself. His concept was later compiled in the 1966 book Theory of Self-Reproducing Automata. Over time, scientists connected this idea to interstellar exploration, suggesting that advanced civilisations could release such machines to explore galaxies.
Ellery, an engineering professor with the Centre for Self-Replication Research (CESER) at Carleton University, has long studied this idea. His work explores how robotics, 3D printing and self-replication could one day allow humans to create similar machines. He believes such technology would offer an efficient way for intelligent life to travel across vast cosmic distances.
Why Would Aliens Use Self-Replicating Probes?
According to Ellery, survival is the main motivation. A civilisation might send out these probes to outlast its dying star, escape a threat, or preserve its species. He told Universe Today that exploration alone rarely drives such missions. Instead, the goal could include gathering resources, reconnaissance, or securing strategic advantages.
Unlike biological beings, those probes would not need air, food, or rest. They could withstand high acceleration, survive extreme environments, harvest materials from asteroids, comets, or moons, and build new copies of themselves. This ability would let them spread rapidly, exploring entire galaxies within a few eons.
What Signs Should SETI Look For?
Ellery proposes a pattern of activity such probes might follow. They would first seek out materials from asteroids and moons, then send out surveyors to explore the system in detail. Afterwards, they would set up bases, replicate more units, and conduct an in-depth, long-term exploration. These actions could result in distinctive traces or technosignatures.
He suggests the Moon is an ideal place to search. Its surface and subsurface metals, possibly influenced by ancient asteroid impacts, could attract such machines. If these probes use nuclear power, traces of isotopes like Thorium-232 or Barium-137 might remain. Ellery even speculates that alien visitors could have left “gifts” buried near lunar resources—artifacts meant to be found once humanity reaches a certain level of technology.
How Does This Change SETI’s Approach?
Traditional SETI focuses on detecting radio transmissions from distant stars. Ellery argues this may overlook what could be much closer. The Solar System itself, he says, offers many hiding spots—from lunar craters to the Kuiper Belt’s millions of icy bodies. “There could be probes everywhere,” he noted, echoing astrophysicist Gregory L. Matloff’s earlier suggestions.
As nations prepare for a new era of lunar and Martian exploration, Ellery urges researchers to include technosignature searches alongside mining and construction surveys. Future missions could investigate odd isotope ratios or magnetic anomalies that could be indicative of alien engineering.
If such probes exist, it would change humanity's understanding of life in the universe. The Moon might hold more than minerals and dust, as Ellery said; it might hold proof that we are not alone.
The study has been shared on arXiv as a preprint.
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