The radio signals from our planet’s airports could be detected by alien astronomers even if their level of technology is the same as our own, according to an upcoming study.
Radar systems used to track planes at aviation hubs such as London’s Heathrow or New York’s JFK could be pumping out radio waves strong enough to be seen by an extraterrestrial civilisation up to 200 light-years away, the researchers found.
The study, led by Ramiro Caisse Saide, a PhD student at the University of Manchester, looked at how radio signals from civilian and military radar operations spread as they move away from Earth, predicting how they might appear by the time they reach nearby stars.
Preliminary results, recently presented at the National Astronomy Meeting, Durham, UK, revealed the radar stations of the world's airports are blasting out their signals at a combined 2,000 trillion Watts.
That’s strong enough for the world’s most sensitive telescope, the Green Bank Telescope, to pick up on an alien planet 200 light-years away.
There are over 1,000 star systems within that distance of Earth, the nearest of which, Proxima Centauri, is just 4.2 light-years away.
Whether an alien astronomer would be able to understand what they were looking at is another matter.
The signal would appear to rise and fall over a 24-hour window as Earth's rotation brought different airports into view, meaning it wouldn't obviously be artificial.
A more obvious signal could come from military radar. Though these tend to be weaker than airport facilities, they are more focused and would appear to flash like a lighthouse in a pattern that is much more obviously not natural.
The biggest limitation on who might be able to spy on our air traffic isn’t the power of radar systems, however, but the laws of physics. The earliest radar system was first broadcast in 1935. As radio waves travel at the speed of light, even these weak, early signals have only had time to travel 90 light-years through space.
The research also helps those here on Earth looking for signs of extraterrestrial intelligence understand how far away they might be able to detect a civilisation at a similar level to our own.
“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,” said Caisse Saide.
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