Nearly four decades after it was received, astronomers still can’t say with 100% certainty that the ‘Wow!’ signal was not an interstellar radio beacon from some far-flung extraterrestrial civilization. But the signal --- which got the Wow! moniker after an astronomer first scribbled those letters in the margins of the incoming data --- was never reacquired.
Even so, Bob Dixon, Ohio State University’s (SETI) Search for Extraterrestrial Intelligence program director at the time, once told me that the signal had to have at least originated at a distance from beyond the Moon.
What is known is that the signal was received just after 11 PM local time on August 15, 1977, at OSU’s now defunct Big Ear Radio Observatory. Its position on the sky came from the direction of the star cluster M55 in the constellation of Sagittarius. Yet more importantly, it closely-matched the narrow emission line of hydrogen at 1420 megahertz , a radio-quiet spot long touted as a potential interstellar hailing frequency for E.T. civilizations. And at the time, it was also the strongest such SETI (Search for Extraterrestrial Intelligence) candidate signal ever seen.
“So, ‘Wow!’ was appropriate,” Dan Werthimer, chief scientist at the University of California at Berkeley’s SETI program, told me. But he says it would be more convincing if the signal had appeared one after another along the Big Ear’s two different radio observing beams.
That, says Werthimer, would be more of an indication that it was an artificial radio beacon from an interstellar point source. But we occasionally see Radio Frequency Interference (RFI) that's modulated in just the right way that makes it look like it is consistent with a distant point source, says Werthimer. But as he emphasizes, if the signal were really from E.T. and was in the telescope’s observing sights for at least a few minutes, the source of the signal should have moved from one beam into the other.
“It didn't,” said Werthimer. “So, I'm 99% confident that the signal the OSU guys saw was RFI.”
Still, there’s another possibility and that is that the signal did originate from beyond the moon, but was produced by two active comets orbiting within our solar system. That is, within the vicinity of the ‘Wow!’ signal’s position on the sky.
A 2015 paper published by The Washington Academy of Sciences proposed that during that summer of 1977, comets 266P/Christensen and P/2008 Y2 (Gibbs) “were transiting in the neighborhood of the Chi Sagittarii star group” and produced by a large hydrogen cloud around their nucleus. Because the frequency for the ‘Wow!’ signal fell close to the radio emission for hydrogen, the paper noted that these local cometary hydrogen clouds would be strong candidates as the signal’s source.
The comet hypothesis sounds somewhat plausible, but I still don’t buy it. If this cometary phenomena were at all statistically frequent, researchers would likely have picked up something similar over the last 50 years. And to my knowledge, this is the first time that anyone has argued that such narrowband emission is from a comet.
My personal best guess is that the signal was not RFI. But more likely, it was the product of some very distant or unusual and/or poorly-understood astrophysical phenomenon.
That’s not to say that E.T. isn’t out there somewhere. But the likelihood that we would only receive a lone radio beacon, that’s never repeated and could never be reacquired, also seems implausible.
Most people can live with the fact that there may be no one out there. Some prefer the notion that we are the ultimate undiscovered country in a cosmos teeming with intelligent life. But few like the idea that we narrowly missed E.T.’s one-off phone call.
Werthimer, however, says either the ‘Wow!’ signal’s rise and fall in strength was actually intrinsic to the signal, in which case he says it would have to be RFI. Or if the signal were from a distant source, he says, then it would be constant in power and its rise and fall in strength would be due to Earth’s rotation.
The remote possibility that it’s the real thing is what makes the ‘Wow!’ signal so haunting . You can dismiss it as Radio Frequency Interference (RFI) until the cows come home. But as Werthimer himself reluctantly acknowledged: “We can't rule out E.T.”
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