Why the ‘Wow!’ signal probably isn’t from aliens after all

Classic science fiction makes it seem as if our first contact with aliens will be absolutely unmistakable: a huge, unearthly spaceship landing on Earth with creatures coming to greet us, or a message that we can somehow translate with ease and confidence. But in reality the search for extraterrestrial intelligence (known as SETI) is a lot more difficult.

[ Related: How scientists decide if they’ve actually found signals of alien life ]

In 1977, Ohio State’s Big Ear Telescope was listening for signals from intelligent life beyond Earth – and to everyone’s surprise, they recorded a transmission that looked like it could be real. Astronomer Jerry R. Ehman was so surprised that he wrote, “Wow!” on the printed data as you view it, giving this signal its name.

“The Wow! signal is fascinating to me because nothing so far has come close to explaining it. It is exactly the frequency you would choose if you wanted to send a radio wave very far through space,” he explains Seven Rasmussenastronomer and author of the upcoming astrobiology book Living in seven numbers. “Personally, it’s my favorite techno signature of all time,” they add. However, the Wow! signal has yet to be discovered, leaving astronomers wondering what caused this strange sighting.

Many things in space actually emit radio wavesand astronomers use all wavelengths of light (including radio!) to study the cosmos. For example, radio waves famously made possible the very first image of a black hole a few years ago. They also helped Jocelyn Bell Burnell discover a strange type of dead star known as a pulsar gas discs revealed that serve as nurseries for planets around other stars.

All these natural sources have something in common: they emit a fairly wide range of radio frequencies. One kind technosignature– a sign of technology, or equivalent, of intelligent life beyond Earth – is a so-called narrowband radio signal. While nature mainly produces broadband signals, technology can produce highly targeted messages.

“To have a truly compelling techno signature, you need something that was created, without a doubt, with intention. The intention can be a tool, or a habitat, or a message, or a work of art. But we should be sure that it cannot happen naturally,” says Rasmussen. “Nature can create right angles (pyrite, bismuth, all kinds of crystals), but not a house, for example.”

Scientists are also considering a variety of technosignatures other than radio images, from the sci-fi concept of a Dyson sphere harnessing the energy of an entire star to more recognizable technological effects such as pollution in a planet’s atmosphere. But the idea of ​​hearing a radio signal from aliens has really stuck in our minds and been immortalized the movie Contact where Jodie Foster listens to a radio telescope with old-fashioned headphones. (It’s worth noting that, unfortunately, real radio telescopes generally don’t work like this: there’s no lightning port to plug your earbuds into.)

Some astronomers are still looking for radio technosignatures (including a repeat of the Wow! signal from the direction of the constellation Sagittarius), such as the Breakthrough Listen project, use radio telescopes such as the Allen Telescope Array in California or the Green Bank Telescope in West Virginia. Yet none of these studies have found anything more compelling than the Wow! signal, which is both narrowband and on a interesting, possibly specially chosen wavelength: 21 centimeters, an important wavelength for one of the lines of atomic hydrogenthe most common component of the universe.

At the same time, other astronomers are working to explain the Wow! signal with natural astrophysics. In one recently posted preprintan international group of astronomers has searched Puerto Rico’s data archives Arecibo Observatoryformerly the largest dish telescope in the world catastrophic collapse in 2020. They found some signals that looked like Wow!, but could easily attribute them to clouds of cold hydrogen floating among the stars. As a result, they suggest that the Wow! signal may have been an astronomical signal master an eruption, a sudden brightening of one of those clouds due to a nearby cosmic explosion. Rasmussen describes this as “the most compelling hypothesis I’ve heard, but I’d like to find the magnetar/SGR responsible for the maser before I say it was definitively a natural phenomenon.”

As radio SETI searches expand, we may find more of these maser flares or other possible outside messages – or perhaps even a repeat of the famous Wow! signal itself.