What is the Wow! Signal?
Everyone remembers the Steven Spielberg’s 1977 classic sci-fi film “Close Encounters of the Third Kind,” which depicted an imagined first contact with an alien civilization. But most probably don’t realize that a few months before the movie came out, real-life scientists believed—at least for a few exciting moments—that they might have detected an actual message sent by extraterrestrials.
It was mid-August 1977, and across the U.S., many if not most people were focused on the shocking death of rock-and-roll great Elvis Presley at age 42. But in Ohio, a 37-year-old man named Jerry Ehman was transfixed by another startling event that—at least for searchers for extraterrestrial intelligence—potentially was even more momentous.
Ehman, a volunteer researcher for Ohio State University’s now-defunct Big Ear radio observatory, pebrused data from the telescope’s scan of the skies on August 15, a few days earlier. In those days, such information was run through an IBM 1130 mainframe computer and printed on perforated paper, and then laboriously examined by hand. But the tedium was shattered when Ehman spotted something surprising—a vertical column with the alphanumerical sequence “6EQUJ5,” which had occurred at 10:16 p.m. EST. He grabbed a red pen and circled the sequence. In the margin, wrote “Wow!”
Ehman’s excitement over that bit of arcane information stemmed from the Big Ear’s mission at the time, which was searching space for radio signals of the sort that might be emanated by extraterrestrial civilizations, if they were attempting to make contact with intelligent life elsewhere in the universe. To Ehman, this signal, which had come from the direction of the constellation Sagittarius, looked an awful lot like it could be such a message. Observatory director John Krauss and his assistant Bob Dixon, who subsequently examined the data, were similarly astonished by it.
But was it? More than three decades later, the Wow Signal, as it has come to be known to SETI researchers, remains both the first and best potential evidence of communication from extraterrestrials, and one of the most perplexing mysteries in science. Over the years, Ehman and colleagues worked to rule out other explanations—such as satellites, aircraft or ground-based transmitters on Earth. But by the same token, researchers have yet to prove that it actually is message from space. “It’s an open question.” Ehman told the Columbus Dispatch in 2010. Or as the late science-fiction author Arthur C. Clarke once put it in a 1997 interview with New Scientist magazine, “God only knows what it was.”
To grasp the significance of the Wow Signal, it helps to understand what Ehman and his colleagues were looking for. Back in the early 1960s, Cornell physicists Philip Morrison and Guiseppe Cocconi had tried to figure out how a distant extraterrestrial civilization, if one existed, might try to contact others in the universe. First, they hypothesized, aliens would use a radio signal, since such transmissions require relatively little energy to generate and can travel huge distances across space. Second, they assumed that the aliens would be smart enough to pick a message that other intelligent species might understand, even if they spoke a very different language. Chemicals, they noted, emit distinctive electromagnetic frequencies, or signatures, which is how astronomers can determine the composition of distant planets and stars from their light. Since hydrogen, the most common element in the universe, emits a signal with a frequency of 1420 megahertz, they reasoned that aliens might send out a signal that mimicked it.
But the signal spotted by Ehman was the first that seemed to fit that description almost exactly.
Each digit on the printout represented the intensity of a radio signal, from zero to 35, with intensities over nine being represented by letters. Most of the signals on the printouts were ones and twos. But this one, as signified by the “U” in the middle, was extremely powerful—about 30 times greater than the ordinary ambient noise of deep space. Indeed, it was the loudest, longest signal that the Big Ear, which was shut down and dismantled in 1997, would ever pick up. And the signal was narrowly focused and extremely close to 1420 megahertz, the frequency of hydrogen. In contrast, natural sources of radiation, such as planets, usually send out a much broader range of frequencies.
While that all has seemed so tantalizing to SETI researchers, they’ve never been able to prove that the Wow Signal actually was such a message. And much about it was difficult to explain. Scientists also were puzzled when they traced the signal to a location northwest of the globular cluster M55—a spot where there apparently was no star or planet. SETI researcher Paul Shuch told New Scientist in 1997 that if the signal did come from an alien civilization, it would have required some amazingly advanced equipment. Assuming that the extraterrestrial beacon was the size of the biggest radio telescopes on Earth, the aliens would have required a 2.2 gigawatt transmitter, vastly more powerful than any existing terrestrial radio station.
But the most puzzling thing about the Wow Signal was that it lasted approximately 72 seconds, and never was detected again, even though in the 20 years that followed, scientists conducted more than 100 studies of the same region of sky. If aliens were trying to contact us, wouldn’t they keep repeating their message? Back in the early 2000s, researchers tried once more with a 26-meter radio telescope in Hobart, Tasmania, which was smaller than the Big Ear but more advanced technologically. Despite their ability to detect signals only five percent as strong as the Wow Signal, the Astrobiology Magazine reported in 2003 that they found nothing that resembled it.