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.’
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.
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.
