Alien probes from far away worlds could already be in our solar system - but we're just too dumb to spot them.
This is essentially the gist of a study by mathematicians from the University of Edinburgh who used massively powerful computers to simulate a multitude of scenarios.
Among their scenarios, was the idea that fleets of hi-tech alien probes invisible to our relatively primitive technology could have explored our galaxy by using a 'slingshot' technique. And the odds, suprisingly, aren't against it.
The researchers said: "Interstellar probes can carry out slingshot manoeuvres around the stars they visit, gaining a boost in velocity by extracting energy from the star's motion around the Galactic Centre,."
Humanity's Voyager space probe uses this technique, but use planets as the slingshot rather than stars meaning the speeds achieved are not as great.
In order to search the entire Milky Way in 10 million years (not long in space terms) our aliens would have to travel at 1/10 the speed of light.
Duncan Forgan and Arwen Nicholson suggest that's entirely possible - and add that the robots could 'self-replicate', re-building themselves from space rocks and dust.
So why have we not spotted them? It could be because they are too well 'cloaked' or, more likely, they're just not here.
Forgan said: "The fact we haven't seen probes of this type makes it difficult to believe that probe building civilisations have existed in the Milky Way in the last few million years."
The findings once again highlight the 'Fermi Paradox' which postulates: Given that alien technology has had time to develop sufficiently within the timeframe of the universe, why have we not seen it yet?
Or more simply: Where is everybody?
The researchers also drew on other previous work in their findings including a 1983 study by Nasa space expert Robert Freitas.
Forgan said: "The probe camouflages itself so as to set up a threshold test of the technology or intelligence of the recipient species, where the test must be met before the species is allowed to communicate with the device."
Dr. Anders Sandberg, of the Future of Humanity Institute at Oxford University, had a more downbeat explanation.
Speaking at the launch of the UK Search for ExtraTerrestrial Intelligence (SETI), he said: "If life or intelligence is rare, it must be millions or billions of times rarer; if advanced societies wipe themselves out, or decide to not go exploring, they need to converge to this outcome with extremely high probability, since it only takes one that escapes this fate to fill the universe."