Humans might not know of any intelligent beings beyond Earth, but if they exist, they might already know about us. New research shows that radar systems at commercial and military airports are inadvertently announcing our presence to any aliens with the ability to listen.
Preliminary results from a study led by Ramiro Caisse Saide, an astrophysics PhD candidate at the University of Manchester, suggest extraterrestrials up to 200 light-years away could theoretically detect electromagnetic signals leaking from global airline hubs such as John F. Kennedy International Airport in New York and Heathrow Airport in London. Military radar systems are also detectable, and thanks to their unique pattern, these signals would look “clearly artificial to anyone watching from interstellar distances with powerful radio telescopes,” Caisse Saide said in a statement.
“In fact, these military signals can appear up to a hundred times stronger from certain points in space, depending on where an observer is located,” he added. “Our findings suggest that radar signals—produced unintentionally by any planet with advanced technology and complex aviation system—could act as a universal sign of intelligent life.” It’s important to note, however, that it will take many more years for signals to reach any extraterrestrial civilizations located 200 light-years away from Earth. Airports and military operations have only been emitting signals of this strength since the 1950s, and therefore, the maximum distance at which aliens could currently detect them is about 75 light-years in all directions.
Seeing as we live in an unfathomably vast, ancient universe with billions of trillions of planets and moons, it stands to reason that we aren’t the only intelligent lifeforms in it. Humanity’s desire to contact extraterrestrials dates back more than 150 years. The first real communication attempt took place in 1974, when astronomers beamed a radio signal from a powerful transmitter at the Arecibo Observatory in Puerto Rico into space. This signal, known as the Arecibo message, consisted of binary code that conveyed information about the basic chemicals of life, the structure of DNA, Earth’s place in the solar system, and even a stick figure of a human. If any aliens received it, they haven’t responded.
That hasn’t discouraged scientists from trying to find them. Those working on the Search for Extraterrestrial Intelligence (SETI) do this passively, scanning space for electromagnetic signals that can’t be explained by natural phenomena. Others have taken a more active approach by intentionally transmitting signals or messages to space, like the Arecibo message. These efforts are called METI (Messaging to Extraterrestrial Intelligence) or CETI (Communication with Extraterrestrial Intelligence). Not everyone believes this is a good idea. Detractors point out that telling aliens where we are could have disastrous consequences if these beings are capable of harming us or our planet.
That’s a scary thought. Perhaps even more frightening is the fact that Earth is unwittingly shouting out our existence and location to any radar-detecting extraterrestrial civilizations within earshot. To get an idea of just how noisy our planet is, Caisse Saide and his colleagues simulated how radar signals from airports proliferate across time and space, then analyzed how detectable they would be from stars such as Barnard’s Star and AU Microscopii. These stars are located roughly 6 and 32 light-years away from the Sun, respectively.
They found that airport radar systems, which sweep the skies for airplanes to inform air traffic control, send out a combined radio signal strong enough for aliens to detect it from up to 200 light-years away using telescopes similar to the Green Bank radio telescope in West Virginia. That’s a vast distance. The nearest potentially habitable planet outside our solar system—Proxima Centauri b—is just over 4 light-years away, and it would still take humanity’s most advanced spacecraft tens of thousands of years to get there. Signals from Earth’s military radar systems are weaker, but more focused and directional, creating an obviously artificial pattern similar to a lighthouse beam sweeping the sky.
It’s important to note, however, that it will take many more years for signals to reach any extraterrestrial civilizations located 200 light-years away from Earth. Airports and military operations have only been emitting signals of this strength since the 1950s, and therefore, the maximum distance at which aliens could currently detect them is about 75 light-years in all directions. But the point of the study stands; aliens located on a planet 200 light-years away should be able to detect airport signals—but not for another 125 years.
Understanding how intelligent extraterrestrials might become aware of our existence can also help guide our search for them, according to Caisse Saide. Identifying and characterizing our own planet’s technosignatures, or detectable signs of technology, can tell astronomers what to look for from other planets, he said. At the same time, “we gain valuable insights into how to protect the radio spectrum for communications and design future radar systems,” said co-researcher Michael Garrett, a professor of astrophysics at the University of Manchester, in the statement. “The methods developed for modeling and detecting these weak signals can also be used in astronomy, planetary defense, and even in monitoring the impact of human technology on our space environment.”
“In this way, our work supports both the scientific quest to answer the question ‘Are we alone?’ and practical efforts to manage the influence of technology on our world and beyond,” Caisse Saide said.
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