Aliens Up To 200 Light-Years Away Could Find Earth Thanks To Our Airports

The first experience that an alien civilization might have of us may not be telecommunications – no ETs watching early The Simpsons episodes. Astronomers have found that up to 200 light-years away, the strongest radio emissions that Earth emits come from airport radar, especially that used by the military. Alien astronomers with similar radio astronomy capabilities to us could be getting the pings from your flight to Ibiza. 

Airport radar systems sweep the skies looking for planes. Doing so, they leak radio waves into space, and it is not an insignificant amount; there are over 40,000 airports in the world, and while not all of them have radar, the ones that do create a combined radio signal of 2x10¹⁵ watts. If aliens within 200 light-years have a telescope comparable to the Green Bank Telescope in West Virginia, they would pick it up.

If we consider just military radar systems, then things are even more interesting for an alien SETI (Search for Extraterrestrial Intelligence). These radars are more focused and directional, creating very specific and different patterns, more similar to a lighthouse sweeping across the sky. The peak emission is just 5 percent of the total combined, but its peculiarity would make it obviously artificial to alien observers.

If we have a civilization out there we the same capabilities in radio domain, could they detect our own radio footprint?

Ramiro Caisse Saide

“Civilizations can actually transmit signals without wanting to do that, unintentionally,” lead researcher Ramiro Caisse Saide, from the University of Manchester, told IFLScience. “We have technology here and produce radio emissions. We want to understand if a civilization with enough technology could detect our own radio emission.”

Saide has previously found that signals from mobile phone masts could be detectable up to 10 light-years away. The radar from airports can reach further afield.

The team simulated how the signal would appear to certain nearby stars. The power will be variable, as the distribution of airport radars is not equal across the surface of the planet. The profile of this space leakage would also depend on from which direction a star is looking at Earth.

The closest star (and exoplanet) to the Solar System is Proxima Centauri, around 4.2 light-years away. The distances between stars might make it feel that 200 light-years is a small distance when it comes to the galaxy (the Milky Way is over 100,000 light-years across), but it is still a big enough volume for over 120,000 stars to exist within that range.

“SETI is a field of study which uses scientific methodologies to assess the question whether we are alone or not in the universe; and we use technology as a proxy for intelligence,” Siade explained. “The idea of my research is to try to understand this: if we have a civilization out there we the same capabilities in radio domain, could they detect our own radio footprint?”

This work was presented at the Royal Astronomical Society’s National Astronomy Meeting 2025, held July 7 to 11.