Did We Just Get a Signal from Extraterrestrials and Not Realize it?

 If extraterrestrials on a distant planet tried to signal us, how would they do it?

We're betting big it will be through an electromagnetic signal. Specifically, we're listening for microwaves. Higher in frequency than your typical FM radio, they travel easily across interstellar distance and don't need all that much energy to make the trip. There's an enormous global effort to monitor the skies for these waves in the hope we hear that first signal from a distant world announcing, "you are not alone." 

The umbrella term for the search is SETI ("Search for Extraterrestrial Intelligence). And there are many well-funded, independent groups around the world focused on this mission. The most well-known might be the SETI Institute the U.S., operating the Allen Telescope Array in Northern California, which combines data from 42 huge radio antennas (each one is 20 feet in diameter) into a single stream able to cover multiple star systems at the same time. But there are many others. In addition to the SETI Institute, there's The Breakthrough Listen at the University of Oxford, the UC Berkeley SETI Research Center, and the COSMIC major radio array in New Mexico. Millions of stars and galaxies are covered - ten times more sky than when SETI began in 1960. 

No single SETI operation is listening 24 hours a day. But all combined, nearly every hour of every day someone on Earth is listening for a microwave signal from an extraterrestrial.

As of today, we've heard absolutely nothing. And it might be because we're listening for the wrong signal. In fact, it might be wrong to "listen" at all.

In 1961, around the same time SETI launched, two men who invented the laser (R. N. Schwartz and Charles H. Townes) had a radically different idea about how aliens might communicate with us. Instead of radio transmission, they proposed lasers could be used to send short, intense pulses of laser light as a form of signaling. The thought was, lasers could be highly directional, less affected by interstellar noise, and potentially carry more data. Advanced civilizations on distant worlds might use visible or infrared light that could be detectable with modified telescopes.

No one jumped on the idea at the time. It remained just an interesting theory for the next thirty years. It wasn't until 1998 that Harvard started an Optical SETI project. In 2001, Lick Observatory followed, targeting stars with large photodetectors looking for this optical way of communicating. And similar to the SETI program listening for radio waves, they found nothing.

Until the night they did.

In 2019, astronomers were operating a 30 inch telescope at the Shay-MEO Observatory in Big Bear, California. The team was led by Richard Stanton, a retired NASA engineer who devoted his time searching for extraterrestrial intelligence. His work was focused on one thing: finding optical pulses from Sun-like stars. 

On this night, Stanton's efforts were rewarded. His team was observing a star known as 51 Pegasi. It's similar to our sun in size, mass, temperature, and age. There's at least one planet orbiting it, and likely more. Maybe one that supported life. On this night, they patiently watched the star, part of their ongoing survey of the skies.

Suddenly, it happened. A pulse. The light from 51 Pegasi increased, then decreased. Then, 1.2 seconds later, it happened again. Two distinct pulses of light sent from 50 light years away.

Stanton reported the find, but it was widely dismissed. Scientists figured it was from passing birds reflecting light from Earth, or atmospheric shock waves -- anything but a signal from extraterrestrials. 

On May 14, 2023 it happened again. Stanton later called it "the only clear, unambiguous signals found to date". These were no birds. Stanton observed two fast, identical pulses of light, separated by 4.4 seconds. They came from another sun-like star, cataloged as HD89389. Several features of the first pulse were repeated almost exactly in the second, including "fine-structure light" observed between the peaks, reproduced exactly in the second pulse. This could not be due to noise or distortions across interstellar space -- the two pulses were the same in intensity and color.

A 95-second exposure photograph of the star-field surrounding HD89389 showed nothing moving past the star as they observed the pulses. After years of methodically searching sun-like stars, Stanton had found his signal. This was the real deal.

In a paper published this year for Acta Astronautica, Stanton makes a plea that we should be constructing arrays of optical telescopes like SETI has done to capture microwave signals. According to Stanton, a single telescope misses the speed of the pulses - you need multiple points of contact. If extraterrestrials are using this method to send us signals, we may not be set up to understand them.

Turns out, we'd better get our act together fast. On January 18, 2025, Stanton and his team observed a third double-pulse event in the light of star HD12051, this time separated by 1.52 seconds.

What are the extraterrestrials trying to tell us? Is it a friendly "hello"? Or a warning? We clearly need different systems set up to truly understand.

We may have been listening for the wrong signal this whole time.