Astronomers searching for signs of life beyond Earth have spotted something strange. An as-yet unexplained radio signal appears to be coming from the direction of the star closest to the sun—a small red star roughly 4.2 light-years away called Proxima Centauri. Adding to the excitement, at least two planets orbit this star, one of which might be temperate and rocky like Earth.

While researchers continue to analyze the signal—and experts caution that there is almost certainly an ordinary, terrestrial explanation—even a remote hint of life beyond Earth has people excited.

“There’s a lot of talk about sensationalism in SETI,” says Andrew Siemion, Breakthrough Listen’s principal investigator. “The reason we’re so excited about SETI, and why we dedicate our careers to it, is the same reason why the public gets so excited about it. It’s aliens! It’s awesome!”

Six decades of searching for extraterrestrials

Scientists have been scanning the skies for radio signals that could be artificial in origin for 60 years—starting with Project Ozma, a search conducted in 1960 by my dad, Frank Drake.

Unlike radio waves the cosmos produces naturally, these whispers from extraterrestrials are expected to look a lot like the transmissions humans use to communicate. Such signals would cover a very narrow range of radio frequencies. They would also have a characteristic “drift” indicating that the source is moving toward or away from Earth—a clue that the radio source is coming from a distant cosmic object, such as a planet orbiting a star.

“Only human technology seems to produce signals like that,” Sheikh says. “Our WiFi, our cell towers, our GPS, our satellite radio—all of this looks exactly like the signals that we’re searching for, which makes it very hard to tell if something is from space or from human-generated technology.”

Over the decades, astronomers have detected numerous candidate signals. Some turned out to come from previously unknown astronomical sources such as pulsars, the rapidly rotating corpses of dead stars that beam radio waves into the cosmos. The first known fast radio bursts—brief blasts of radio waves that are still somewhat mysterious—initially seemed as though they could be artificial signals. Signals called perytons, which are less energetic bursts of radio emission, also raised eyebrows until scientists determined their origin: a microwave oven.

BLC-1 could be beaming from an object that isn’t transmitting as expected: a satellite that hasn’t been identified yet, a plane traveling overhead, a transmitter on the ground near the telescope’s line of sight, or perhaps something even more mundane, like faulty electronics in a nearby building or a passing car.

“We’re looking for something else out there, someone else out there,” Tarter said at the time. “To suddenly see interference, and think it might be what we’re looking for, and then figure out what we have to do to be able to discriminate and to have confidence in any result that we might get—that’s a good lesson.”

Already, Siemion says that evaluating BLC-1 has taught the team a lot about testing their data. Follow-up observations of Proxima Centauri will be valuable for understanding how such stars behave—as well as for achieving a comprehensive SETI search of a nearby star system with known planets, even if it isn’t populated by technologically savvy aliens.

“Ultimately, I think we’ll be able to convince ourselves that [BLC-1] is interference,” Siemion says. “But the end result will certainly be that it will make our experiments more powerful in the future.”