Back in April 2019, an Australian telescope picked up a very tantalizing radio signal that seemed to emanate from the sun's closest neighboring star. The signal didn’t have any obvious explanation. Instead, it seemed to possess the hallmarks of something created by intelligent alien life.
And in fact, that was the whole point of the research project that stumbled on the signal. Called Breakthrough Listen, the $100 million effort has spent the last five years using state-of-the-art telescopes around the world to listen in on signs of extraterrestrial life from around the galaxy.
The 2019 signal, called “blc1,” was exactly what the Breakthrough researchers were hoping to find. Detected by the Parkes Murriyang radio telescope in southeastern Australia, blc1 was coming right from Proxima Centauri, a star just 4.2 light-years away, and home to two planets—one of which is thought to be potentially habitable to life.
According to Sofia Sheikh from the Berkeley SETI Research Center, the signal was “uniquely similar to the kind of signal we would expect from space.” It was something that could only be made by technology—and technology from space to boot. It lasted several hours, which ruled out satellites or aircraft. If it had a natural origin, the signal should have repeated over time, but the team never observed it again in dozens of hours of follow-up observations of Proxima Centauri. Instead, it was the type of one-and-done signal expected from an intelligent civilization.
Over the last two years, the Breakthrough team has pored over the data and finally come back with a verdict on blc1.
Bad news: It’s not aliens.
“We can confidently say that blc1 is consistent with human radio frequency interference from some sort of ground-based technology,” Sheikh, a co-author of two new studies on blc1 published in Nature Astronomy, told The Daily Beast. “While of course we would love to find evidence of extraterrestrial life someday, the process of investigating blc1 was extremely scientifically valuable in its own right.”
Over the two years of analysis, the team found out that blc1 actually shares the same frequency as other radio interference that was picked up around the same time as blc1’s detection. A deep dive into the data found over 60 “copies” of the blc1 signal, all with very clear signs of being radio interference.
Though the team still doesn’t know exactly what created blc1, an alien origin has been ruled out.
Sheikh and her colleagues don’t consider this investigation to be a total loss. In her view, it’s an opportunity to improve the algorithms designed to weed out human interference, and improve the process designed to help evaluate this type of data more thoroughly. She’s also glad they have the type of hardware and software that can more rigorously scrutinize these signals these days. The infamous “Wow!” signal—named after scientists who observed it wrote “Wow!” on the readout of the data—was a similarly extreme blip detected in 1977 in Ohio, but scientists were unable to trace its origins.
“Without this new technology, a one-off signal like blc1 would remain in limbo as ‘maybe it was, maybe it wasn’t,’ like the Wow! signal,” said Sheikh.
The new findings are a drag, but scientists aren’t done with Proxima Centauri. NASA’s James Webb Space Telescope, billed as a successor to Hubble and launching next month, could detect signs of life on one of the star’s planets. And Breakthrough Listen’s sister project, Starshot, is planning to one day build and launch a fleet of small spacecraft to Proxima Centauri to get a glimpse of any alien life up close. That plan involves a giant laser cannon that may or may not be impossible to build, so we’ll wait to see how it pans out.