Here on Earth, scientists use huge radio telescopes to scan the skies for signs of advanced alien civilisations hiding out in space.
But what if the aliens are doing the same thing?
Scientists have revealed that radar systems at airports and military bases would shine out like cosmic beacons for any watching civilisations.
This means airports like Gatwick and Heathrow could be revealing our presence to aliens.
Research presented at the Royal Astronomical Society’s National Astronomy Meeting simulated how Earth would look to an alien civilisation if they had state-of-the-art radio telescopes like our own.
This revealed that a civilisation would not need to be particularly advanced or particularly nearby to spot the signals leaking from Earth’s airports.
Professor Michael Garrett, an astrophysicist from the University of Manchester and director of the Jodrell Bank radio telescope, told MailOnline: ‘I don’t think they need to be more than a few hundred years more advanced than we are.
‘So they don’t need to be something like a “Star Trek civilisation” way more advanced than us, just to detect our signals.’
Humanity might be revealing its presence to the universe by leaking radio signals into space, according to new research (stock image)
Scientists say that radar dishes at airports like Gatwick (pictured) could be giving away our presence to alien civilisations
Aliens within 200 light years would be able to pick up radio waves emitted from Earth, even if they were only 100 years more advanced than us (stock image)
Radar systems, like those used at airports, detect planes by sending out beams of radio waves and measuring how they bounce back from distant objects.
But as radar systems look for planes, those beams of radio waves also leak out into space.
Professor Garrett and lead author Ramiro Caisse Saide, a PhD candidate at the University of Manchester, looked at how this invisible electromagnetic radiation would look from beyond the planet.
They found that Earth’s civilian airports alone reach peak emission intensities of two billion megawatts.
This is so strong that a radio telescope comparable to the Green Bank Telescope in West Virginia could pick up the signal from 200 light years away.
For context, the nearest plausibly habitable world to Earth is Proxima Centauri B, located just four light years from Earth.
Although it would still take thousands of years to get there with our current technology, it is well within the range needed to pick up our radio signals.
The radar signals emitted by military installations would be an even stronger giveaway of humans’ presence in the universe.
Researchers simulated what Earth would look like to an alien radio telescope located at Barnard’s Star, located about six light-years from the Sun
3Even as far as AU Microscopii, a star located 31.7 light-years from the sun, Earth’s airports would light up like cosmic beacons to any watching civilisation
Unlike civilian radar, military systems have a much more focused beam which sweeps the sky like a lighthouse.
Depending on where the observer is located, these signals can be up to 100 times stronger than those emitted by an airport.
Mr Saide says that these would look ‘clearly artificial to anyone watching from interstellar distances with a powerful radio telescope.’
To any alien civilisation who might be watching, this ‘technosignature’ would be a clear sign of intelligent life on Earth.
‘Our findings suggest that radar signals – produced unintentionally by any planet with advanced technology and complex aviation systems – could act as a universal sign of intelligent life.’
However, the researchers say there’s no need to start shutting down the airports over fears of an alien invasion.
Professor Garrett says: ‘The likelihood is that technical civilisations are quite rare and perhaps they don’t persist very long. Civilisations rise and fall, and if you are bound to a planet, resources are limited.
‘So the Universe is big, it’s also really old, and if technical civilisations are short-lived, they can come and go in our own Galaxy all the time, but never overlap long enough to detect each other.
Military radar systems were particularly obvious due to their clearly artificial sweeping patterns. This would be a clear sign of intelligent life to a watching alien
A telescope comparable to the Green Bank Radio Telescope in West Virginia (pictured) could pick up Earth’s radio signals from up to 200 light-years away
The nearest potentially habitable planet, Proxima Centauri B (artist’s impression), is just 4.24 light-years away. This means we would be able to spot any signals of intelligent life by their leaking radio waves
‘So I’d say, we shouldn’t worry too much about radar powers – of course I might be wrong!’
The more exciting implication of these findings is that Earth’s radio signals might give us a hint at what to look for in our own search for extraterrestrial life.
Generally, most research projects looking for alien technosignatures scan for powerful signals in narrow bands of the electromagnetic spectrum.
These simulations show that weaker broad-band signals like radar emissions can also be a clear sign of intelligent life.
The only issue is that an extra 100 years of advancement might give aliens forms of technology we struggle to detect or even recognise.
However, Professor Garret remains hopeful that spotting intelligent life remains possible.
He says: ‘I think AI will push our own civilisation further forward by a huge amount in the next 30 years, the detection of an extraterrestrial signal might just be around the corner.’
