'Self replicating' robotic space probes from alien civilisations could already have arrived in our solar system - but we don't have the advanced technology to detect them, a new study has claimed.
Researchers from Edinburgh University believe alien races could have used the gravity of stars to 'slingshot' probes in order to gain speed: a technique humans already use for probes, such as the Voyager.
The Voyager space probe uses a 'slingshot' technique but uses planets rather than stars as the Scotland-based mathematicians suggest, 'The Independent' reported.
The researchers also analysed how a fleet of probes could 'self replicate' and build new versions of themselves from dust and gas while travelling through space.
The probes could be so hi-tech that they're invisible to human beings, said mathematicians Duncan Forgan and Arwen Nicholson.
"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," Forgan said.
According to the researchers' calculations, alien probes would only need to travel at one tenth of the speed of light in order to explore every part of our galaxy within 10 million years.
"We can conclude that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time...orders of magnitude less than the age of the Earth," researchers concluded.
The study was published in the Journal of Astrobiology.