You might think that humanity’s best chance of finding a̳l̳i̳e̳n̳ life involves peering deep into space and analysing faraway galaxies.
But a NASA study has suggested the truth about e̳x̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳s could be lurking right under our noses.
Dozens of space scientists have teamed up to explore how our species could detect ‘technosignatures’, the name for pieces of evidence which give away the presence of advanced a̳l̳i̳e̳n̳ civilisations.
Some of these tell-tale signs are obvious. For instance, if loads of radio waves are detected coming from a distant star system, then it could be a clue which shows it’s inhabited by intelligent e̳x̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ organisms.
We could also search for a̳l̳i̳e̳n̳ societies by looking for ‘megastructures’ called Dyson Spheres, which are theoretical power stations built surrounding a star to harvest its energy.
These would be easy to spot because they are likely to be gigantic and block out starlight whenever they pass in front of their sun.
Other technosignatures are harder to identify, such as evidence that a planet has been polluted by heavy industry.
In the new report, scientists also make the fascinating suggestion that our own planet may be hiding a̳l̳i̳e̳n̳ ‘artefacts’, some of which may even have been built by extinct civilisations which lived on Mars, Venus or even Earth.
‘Because the geological, paleontological, and archaeological records on Earth are so incomplete, it is even possible that the Earth itself hosts such artefacts, although, again, this idea is often conflated with unscientific popular imaginings and science fiction stories about a̳l̳i̳e̳n̳ visitation, and so must be approached carefully,’ researchers wrote.
‘If technosignatures were discovered in the solar system, it would be worth considering whether their origin might not be interstellar.
‘Specifically, since the Earth is home to the only known species capable of interstellar communication and planetary travel (although both technologies remain in their early development), the Earth remains the only known planet fecund enough to promote technological life, and so it or an early, habitable Mars or Venus could even be the origin of such technology.’
So far, our species has only spotted one potential a̳l̳i̳e̳n̳ artefact, although most scientists believe its origins are natural rather than artificial.
A comet or asteroid or a̳l̳i̳e̳n̳ spaceship called ‘Oumuamua sped through our solar system in 2017 at high speed. It was the first ‘interstellar visitor’ to be observed in our stellar neighbourhood after traveling here through deep space.
It changed direction as it passed the sun, which may have been caused by a natural process called outgassing – although there is a very slight chance this could have been the result of it being steered somehow.
Some scientists suggested ‘Ouamuamua was an a̳l̳i̳e̳n̳ probe, whilst others went on to suggest our solar system could be full of similar e̳x̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ spacecraft.
Sadly, the consensus is that it was a comet ejected from a farway star system and sent on a long journey through the void.
In the latest study, scientists added:
‘Technosignatures in the solar system might come in the form of free-floating probes or structures — either passing through the solar system or in orbit around the Sun or other body — or in the form of structures or other signs of technologies on planetary surfaces.’