Astronomers Are Keeping a Close Watch on the Next Star Over

Last month, as 2020 drew to a close and we on Earth completed one of our strangest orbits around the sun, news broke that astronomers had picked up a mysterious signal from another star.

Astronomers could tell, from the specific properties of the beam of radio waves, that it wasn’t made by an act of nature, such as a cosmic explosion. The signal coming from the star’s direction was produced by technology.

The signal, known as BLC1, was intriguing, but when news of its detection leaked to The Guardian, the astronomers who detected it—and others in the field—were quick to point out that although the transmission came from some kind of technology, the technology probably belonged to us. In the weeks since the news emerged, the researchers have done more work, and they believe that although the signal is artificial, it’s probably not the work of aliens.

“There’s nothing about it that says it’s clearly some alien intelligence trying to send us a message,” Sofia Sheikh, a graduate student at Pennsylvania State University who is leading the team studying the signal, told me recently. Sheikh is a member of Breakthrough Listen, a program funded by a Russian billionaire that searches for evidence of alien communications. “There’s no information carried in the signal. It’s just a single tone, like a foghorn. In fact, it looks very much like the things we produce on Earth.”

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But in at least one sense, the news is different from similar findings made in recent years. The star, known as Proxima Centauri, is too faint to see with the naked eye, but it is the closest star to Earth. If human beings ever leave the bounds of their star and head toward another, they will probably go to Proxima. There might be nothing there, not a colony of microbes nor a community of advanced beings. But as far as listening goes, in the effort to search the cosmos for a sign of something both familiar and extraordinary, Proxima might be a sensible target.

Proxima—Latin for “nearest”—is located just 4.2 light-years away, in a triple-star system known as Alpha Centauri. Since its discovery in 1915, Proxima has regularly appeared in science-fiction tales of interstellar arks and alien empires. When the field of SETI—the “search for extraterrestrial intelligence”—began in earnest in the 1960s, Proxima was one of the first places researchers considered. When your search spans the observable universe, proximity certainly matters.

Unlike its two sibling stars in Alpha Centauri, Proxima is not like the sun. It is smaller, cooler, and dimmer. But it does have at least two planets. One of them, known as Proxima c, orbits farther from the star, like a miniature Neptune. The other, Proxima b, is closer in—so close that its year lasts only 11 days. Proxima b is rocky, about the same size as Earth, and within the star’s habitable zone, a region where temperatures might allow water to flow on its surface.

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We don’t know what Proxima b looks like, and the astronomers studying BLC1 aren’t suggesting that the beam originated there. Contrary to some early sci-fi tales, Proxima b would make a terrible second home for us, and might not be an easy place for any kind of life to take hold, despite its potentially balmy climate. Stars like Proxima Centauri are known to unleash torrents of radiation, enough to strip a nearby planet of its atmosphere over many years.

The public’s enthusiasm about BLC1 might have been premature, but if humankind ever does hear from an advanced alien civilization, the call could come from nearby. It might sound presumptuous to suggest that, out of the hundreds of billions of stars in the Milky Way, we could discover intelligent life on the next one over. And, well, it is pretty presumptuous. But it’s not impossible. “It’s probably slightly more likely that we would find intelligent life on Proxima than anywhere else,” Sheikh said. “Assume that aliens are everywhere, [that] every star has a humanlike civilization, then they might all be saying hi. But the one we’re gonna see first is the closest, because that will be the one that we’re able to detect.”

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Let’s say an advanced civilization on one star wants to reach the inhabitants of another star many light-years away. To communicate over such vast distances, it might establish a network not unlike cellphone towers, allowing it to bounce radio signals from star to star. “Point-to-point communication among stars is very hard, because the signals get weak so quickly in space,” Jason Wright, an astronomer at Penn State and a member of Breakthrough Listen’s advisory board, told me. “It’s not at all unreasonable that, under this scenario, Proxima would be the first place—maybe the only place—that we would see signals coming from.”

This scenario assumes that our sun is just one stop in a giant, invisible network whose creators are unaware of our planet’s existence. What if the message were addressed directly to us? “If aliens were trying to get our attention,” Wright explained in a recent blog post, “they’d have to guess which stars we’d guess to search for their signal. There are a lot of stars to choose from—which is the most obvious place for us to look?” Hello, Proxima.

Listening for signals from Proxima Centauri is one thing; going there would be quite another. The missions that have traveled farthest into space, NASA’s Voyager spacecraft, won’t even leave our own solar system for tens of thousands of years. If we dispatched another set of those spacecraft right now, it would take them more than 70,000 years to reach Proxima Centauri. Yet another exploration program, backed by the same Russian investor, is seeking to send tiny, laser-propelled spacecraft to study the Alpha Centauri system within the first half of this century—a journey it hopes will take a mere 20 years. “We do not know how to travel there yet, but it’s the first system where it’s not crazy to actually say that you’re thinking about interstellar travel,” says Lisa Kaltenegger, an astronomer and the director of the Carl Sagan Institute at Cornell who was not involved in the new research.

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Sheikh and her colleagues plan to publish an official report soon, and BLC1 will likely join a group of other once-tantalizing signals that turned out to have a far more mundane source, such as a Russian military satellite or ordinary cosmic dust. Terrestrial sources of radio waves, from kitchen microwaves to high-flying satellites, can easily sneak into observations. Sheikh and her team are closely examining the radio environment around the Parkes Observatory in Australia on the day its telescope caught the signal, looking for a potential explanation—even something as simple as radio waves wafting through an open door, Sheikh said. In 1998, astronomers at the same observatory started detecting strange radio signals in their observations that went unexplained for 17 years until a new receiver was installed and uncovered the source: a microwave the staff used to heat up their lunch.

Despite the allure of Proxima’s, er, proximity, the cosmos is brimming with stars worth investigating. A decade ago, Jill Tarter, an astronomer and the co-founder of the SETI Institute, calculated that astronomers had searched a volume of space equivalent to only one glass of all of Earth’s oceans combined. Others have updated the estimate; it’s a hot tub now. SETI is a long game. “You don’t get up in the morning and say, ‘Today’s the day I am going to find a signal,’” Tarter told me recently. “Because odds are, that night, you will go to bed disappointed.”

Yet Tarter is hopeful. Finding the real deal would not only help us understand our place in the cosmos; it would also suggest that if we play our cards right, our civilization could survive for many more orbits than we can imagine. Making contact now would mean that they—whoever “they” are—are close enough to our cosmic neighborhood not only in space, but also in time. They’re transmitting while we’re searching. “The only way that’s going to happen in a galaxy that’s 10 billion years old is if, on average, technological civilizations are long-lived,” Tarter said. “So if we succeed in SETI, it tells us that we can have a long future. Somebody else figured out how to make it through, so we can figure it out too.”