Astronomers Don’t Think That So-Called SETI Signal Is Aliens—and Neither Should You
This weekend, a group of astronomers made many, many headlines after giving a presentation about “a strong signal in the direction of HD164595.” HD164595 is a Sun-like star 94 light-years away, and with the RATAN-600 radio telescope in Zelenchukskaya, Russia, pointed in its direction, the astronomers picked up a blast of radio waves about 4.5 times stronger than background static. Maybe aliens? they suggested. We should investigate.
Their presentation began circulating among astronomers in slide-deck form. Paul Gilster at the website Centauri Dreams wrote about it as “an interesting SETI candidate”—meaning perhaps it came from an extraterrestrial civilization. That set off the media storm.
But I have to tell you something: Astronomers don’t know much about that “SETI candidate” signal beyond that it’s made of radio waves. And while human beings should absolutely spend some time figuring out what this signal is, they have almost no reason to conclude it came from non-human beings. Here’s why:
They don’t actually know it’s coming from that star.
As Seth Shostak, senior astronomer and director of SETI research at the SETI Institute (how’s that for credentials?) noted, the telescope doesn’t see a fine point in the sky. Every telescope has a “field of view.”
The RATAN’s view isn’t circular, though. It catches a narrow east-west section, which in this case was centered on HD164595. But the north-south view is “highly elongated,” Shostak wrote on the Institute’s website. And the actual source of the mysterious radio waves could be anywhere inside that elongation: The telescope’s “field of view” is just one strangely shaped pixel. We normally think of pixels as small, focused dots, like the kind that come from our cameras. But all “pixel” really indicates is that all of the light from a specific area gets lumped together, and basically averaged. The radio waves “from” HD 164595, then, could be coming from a little north or south of the star’s actual position, and scientists wouldn’t be able to tell the difference.
They don’t know if it’s a narrowband signal.
Historically, SETI programs have searched for “narrowband” signals spread over just a few frequencies, because scientists think it takes technology to squish a signal like that, like we do with radio-station broadcasts (nature’s narrowest radio signals seem to span around 300 Hz). A squished signal equals “Someone might have made it on purpose.” So SETI scientists collect radio waves from the sky and split them into their constituent frequencies, to see if a strong spike shows up in one or a few bands. The SETI Institute’s Allen Telescope Array splits signals into hertz-wide chunks—a billion times smaller than the RATAN-600’s data, which was in a gigahertz-wide chunk.
Like the telescope’s single pixel, which lumps all the waves from one area together, the telescope’s electronics lump 1 gigahertz’s worth of frequencies together. Was the original signal narrowband? Wideband? These data can’t—ever—tell that story. As the [email protected] program, which uses citizens’ computers to comb through data for suspect radio waves, noted on its website, “Because the receivers used were making broad band measurements, there’s really nothing about this ‘signal’ that would distinguish it from a natural radio transient (stellar flare, active galactic nucleus, microlensing of a background source, etc.).” There is, in fact, an entire field of study devoted to signals like this: time-domain astronomy, which includes, yes, SETI, but also any other signal that appears, disappears, and reappears or doesn’t. It happens a lot. Space is busy. So are human devices.
They don’t know it’s not human-generated interference.
While astronomers don’t know if this signal is squished or spread-out, they do know the middle frequency that the telescope was sensitive to: around 11 gigahertz.
Two things: Radio telescopes are supposed to catch cool waves from space. And they do that. But they also catch less cool waves from Earth, or from Earth-orbit. Airport radar, Wi-Fi, spark plugs, cell phones, and basically anything that runs on electricity emits radio waves. And satellites use these frequencies to ping and downlink. The research team has not presented data to rule out humans as the signal’s makers. In fact, one will note that 11 gigahertz is in the exact middle of a band of the radio spectrum allocated to “fixed satellites.”
“We see signals that come and go every day, all the time,” says Gerry Harp, Director of SETI Research at the SETI Institute. “We would not have given much credibility to this signal in our survey. It would be one of so many others, and they are almost always local interference.”
They don’t know it’s not a fluke.
The team, led by Nikolai Bursov of the Russian Academy of Sciences’ Special Astrophysical Observatory, scanned the star 39 times. They saw this signal once. At the Allen Telescope Array, the automated detection system checks on a candidate signal five times in a row, performing two tests each time. Those, says Harp, plus one or two at the beginning and end, mean a suspected SETI signal has to pass 12 total tests before the software tells people to pay attention (Harp says that has only happened once in the Allen Telescope’s history). The HD164595 signal, instead of passing 12/12 tests, has passed just 1/39. “In our system, we would have just forgotten about it and carried on,” says Harp.
The [email protected] program “has seen millions of potential signals with similar characteristics, but it takes more than that to make a good candidate,” the team wrote in a blog post. “Multiple detections are a minimum criterion.” The SETI Institute hasn’t seen it again, so far, in observations their telescope began after the announcement, although they have not yet searched the full gigahertz of potential frequencies.
They didn’t tell other telescopes soon enough.
This candidate SETI signal came in more than a year ago, in May 2015. The researchers didn’t say anything until now. And if it were aliens, they may have turned their “Notice us! We’re awesome!” beacon off in June or something.
In the SETI world, one of the first items on an excited astronomer’s agenda—upon perhaps making the most meaningful cosmic discovery in the history of humans—is to ask other telescopes to look at the same star system. This can help rule out ground-based annoyances, which wouldn’t show up at an observatory following up across the country. It also rules out weird internal problems a given telescope might be having. The fact that the researchers didn’t tell anyone for more than a year, and so precluded these standard check-ups and confirmations, suggests maybe they didn’t think it was from aliens, either.
Look, I’m super pro-discovering-extraterrestrial life. It would fundamentally alter our view of the universe, ourselves, and what the two mean together. If it happens, I will cry and cry and write some article and throw a huge party, and I will invite you. But there’s almost nothing about this “candidate signal” that says “aliens,” besides that it’s a radio signal that might be from space, and it would have had to be strong to show up like this if it did come from that many light-years away.
Let’s rule out satellites and other interference; let’s cross quasars and other banging celestial objects off the list; let’s try to catch the waves again; let’s see if they look engineered or astronomical. Then we’ll talk.
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