Earth hears a possible signal: We are here, we are here, we are here

In a year that has brought an impeachment, a raging pandemic, far too many tragic deaths, a hopeful election, and months of increasingly aggressive sedition aimed at overturning the government of the United States, could there still be a story to top them all. Well … maybe. 

The biggest story of 2020 might be one that didn’t hit the press until mid-December. Or it could be nothing. Because back in April and May, for a combined period of 30 hours, scientists at the Parkes Observatory in Australia listened in on a signal. A radio signal. One that they believed to be coming from the sun's nearest neighbor, Proxima Centauri. The nature of that signal could rock humanity’s beliefs about the universe and introduce perhaps the most groundbreaking discovery in history. Or it might have been someone warming a burrito. Despite what the wild-haired guy says on cable, it’s not aliens, because it’s never aliens. But the longer people have looked, the more of the “easy explanations” have been eliminated.

The story first leaked to The Guardian on Dec. 18. That the researchers involved, and those carrying out the analysis, sat on the data for eight months without spilling the beans makes it clear they understood exactly the reaction that comes any time someone pops up claiming to have discovered a possible sign of intelligent life in space. There will be jokes. The words “little” and “green” will be used. And skepticism tends to run right past the bounds of appropriate into dismissive.

There are very, very (and … very) good reasons to be skeptical. Not least of all because several past natural phenomena have first been thought to be potential signals of intelligence before astronomers and physicists figured out just how “clever” nonliving matter could be. In the most cited example, pulsars—regular points producing rapidly repeating patterns of “signals” at both radio and other wavelengths—turned out not to be either massive transmitters or some spectacular variety of space pharos. Instead they are the rapidly spinning neutron star cores left behind by exploded giant (but not supergiant) stars. Which kind of makes it not all that surprising that it took a bit for someone to find the explanation.

In another famous (or infamous) case, what had appeared to be a set of signals recurred so frequently that they were given a name: perytons. These signals kept returning over and over for 17 years, baffling scientists until the installation of a new instrument revealed that the mystery signals actually came from a microwave oven at the facility. And what facility would that be? Why, Parkes Observatory in Australia. That was just five years ago.

Oh yeah. You better believe they are checking everyone’s lunch schedule.

Another good reason to be skeptical of this report is that the researchers involved seem to have found exactly what they were looking for. This data was collected by the Breakthrough Listen project, a SETI (Search for Extraterrestrial Intelligence) project founded in part by Stephen Hawking and funded primarily by Israeli-Russian tech billionaire Yuri Milner. The signal itself was first detected by a student, Shane Smith, who tagged it as BLC1, for “Breakthrough Listen Candidate 1.” That’s right. This is the first candidate they’ve found.

Anyone who stumbles across the very thing they hoped to locate, and does so practically in their own backyard, has to be held to quite a high standard of proof.

However, as Scientific American reports, after months of wading through the data, searching for possible sources of interference, and reviewing the contents of the signal, the scientists involved remain hopeful. The signal appears to come from a point source at distance rather than something close at hand. It also appears to be quite narrow in bandwidth, which would be somewhat unusual for a natural source. Finally, not only does the signal appear to originate from the area of Proxima Centauri, the researchers believe it shows signs of a regular shift that might be expected if the source was actually a planet orbiting that star.

As it happens, Proxima Centauri is quite a complex little system. It’s a red dwarf star, the most common kind of star in the universe, quite a bit smaller and cooler than our sun. In fact, it’s so small and cool that, despite being the nearest star to our own, it can’t be seen by the naked eye. (It also can’t be seen at all from the Northern Hemisphere, so plan a trip and bring at least a good pair of binoculars.)

This small star is believed to  orbit around the binary star Alpha Centauri A and Alpha Centauri B. (Proxima is also known as Alpha Centauri C.) Those stars are larger yellow stars, more similar in size and temperature to the sun. Exactly what that orbit looks like, or how long it’s been going on, is the cause for a lot of computation and a lot of frustration. (Read Three Body Problem from Chinese science fiction writer Liu Cixin if you want to understand more about why this is so difficult to suss out.)

Little red Proxima is known to have at least two planets which, for perfectly sound planet-hunter reasons, are known as Proxima B and Proxima C. Proxima C is about 7 times the mass of Earth, making it roughly the same size as Neptune. However, it’s not clear if the planet is actually a gas giant or just the kind of oversized rocky world known as a “super Earth.”

Proxima B is where it really gets interesting. The planet is located very close to the star, much closer than Mercury is to the Sun. So close, in fact, that Proxima B’s “year” is just 11 days long. However, because Proxima Centauri is so much smaller and cooler than our sun, this close orbit places Proxima B squarely in the “habitable zone.” Which means nothing except that the level of radiation received by the planet is such that it could potentially have liquid water on the surface. Water is something that scientists believe is critical to everything we understand as life. Proxima B is also not a lot larger than Earth—about 1.17 times the mass of Earth. As far as Earth-like exoplanets go, Proxima B is a pretty decent candidate.

And, in interstellar terms, it’s right next door. Like right next door. This is absolutely the closest star out there. Why, it’s so close that if the Voyager 1 probe happened to be aimed in the right direction (it’s not), it would pass by Proxima in just … 71,000 years. 

Space: It’s big.

There are reasons to be dismissive of the idea that there could be life on Proxima B. For one thing, red dwarf stars may be smaller than yellow stars like our sun, but they also tend to be rather grumpy. Red dwarf stars have frequent storms and eruptions that would hit a close-orbiting planet like Proxima B with so many energetic particles it might quickly strip away any atmosphere. Not all scientists think this is the case, but if there’s going to be life around red dwarf stars, it would take some mechanisms we don’t yet understand. In Proxima’s case, there is also the complication of that maybe-orbit around the Alpha Centauri binary star, which could cause serious instability over time both for the red star and its planets.

Breakthrough Listen has been going to sites around the globe, buying up time on radio telescopes, and listening in for signals like what seems to have been detected at Proxima. It is definitely the hottest show in the whole of the many decades of SETI. So, as might be expected, is … completely skeptical. Their latest news release contains what amounts to a sneering dismissal of the possible signal from Proxima Centauri. 

Besides emphasizing that this is only a candidate, the biggest thrust of the article is just how unlikely it would be to encounter intelligent life at the next system over. Not just intelligent life, but life at a technological stage so similar to our own that it’s using radio signals that we can detect and possibly identify. All of which is a pretty good point. In fact, the director of Breakthrough Listen has announced that the signals are “likely interference” that will soon be explained. 

Still, as SETI researcher Franck Marchis says in his conclusion … 

2020 has been a crazy year on so many levels, even in the field of SETI. After the mysterious appearance of monoliths and the announcement of the galactic federation, we now have BLC1, a curious and mysterious signal that might—or might not—have come from Proxima Centauri. It’s probably not alien and we will confirm this soon. Of course, as a SETI Institute scientist, nothing would please me more than to be proven wrong.