The signal from the stars arrived at the Big Ear radio observatory in Ohio at 11:16 p.m. on the night of August 15, 1977. It came in loud and crisp, reaching at least 30 times the volume of the background noise and occupying a single 10 kilohertz-wide band on the observatory’s receiver. Its middle part lasted 38 seconds – the time it takes Big Ear’s radio band to traverse a single point in the sky – and it landed almost precisely at the frequency at which SETI scientists were hoping to find it: 1420 megahertz, the emission frequency of hydrogen. It was exactly what SETI scientists had been waiting for – a seemingly artificial signal from the stars, one that could carry a message from alien beings light-years away.
No one was there to receive the signal when it came in. The telescope’s beam silently scanned the skies, the receiver and spectrometer registered and analyzed the data, and a printer rattled in the darkness, recording it all in a continuous stream of numbers and letters. But when Big Ear volunteer Jerry Ehman looked over the printout a few days later, the sequence recording the signal leaped off the page at him: 6 E Q U J 5. Ehman circled the sequence and in the margins jotted a pure, barely articulate, expression of wonder: “Wow!” That was the first time the Wow! signal was detected. To this day, it is also the last.
Strong and clear though it was, the Wow! signal disappeared almost as soon as it was found. It was received by one of Big Ear’s two beams which follow each other across the sky in close succession, but not by the other. This alone means that it was not a long continuous signal, but an intermittent one. Even an intermittent signal should be found again eventually, and Big Ear’s team returned to the location in the sky where the Wow! signal originated more than 50 times hoping to catch it. They found nothing. To most SETI scientists the Wow! is the single most intriguing result ever produced by the Search for Extraterrestrial Intelligence. But with no follow-up detections there is simply no way to know whether it was truly a signal from the stars.
No one has spent more time and energy searching for the Wow! signal than Bob Gray, author of The Elusive Wow: Searching for Extraterrestrial Intelligence. Gray is not a professional astronomer, the kind that works in an academic department and receives a steady paycheck from a university or an observatory. Gray makes his living as a data analyst, which means that in radio-astronomy he is technically an amateur – in the best sense of the word: one who does his work as a labor of love. But when it comes to the nuts and bolts of mounting a search for extraterrestrial intelligence, he is as professional as they come.
The Big Ear Observatory
Gray first heard of the Wow! signal a few years after its detection, and was fascinated by its potential implications. He contacted the Ohio team, visited Big Ear, and had long conversations with Jerry Ehman, as well as with Bob Dixon, who was the director of the SETI project, and John Kraus, the telescope’s designer. The discussions convinced him that the Wow! was not a hoax or a case of terrestrial interference, and most likely originated from the stars. But he also learned that apart from the Big Ear team’s own sporadic efforts no one else had actually tried to find it again.
Gray was surprised. Given the momentous nature of what the Wow! signal could reveal, he expected astronomers to be clamoring for a chance to study it. But this was clearly not the case. The reason, he came to realize, is that observing time on the world’s great radio telescopes is a rare and much sought-after commodity. Once scientists secure a few hours or days on one of those great dishes, they understandably use every minute of it to pursue their own research projects. They simply have no time for romantic pursuits like a search for aliens.
But as an outsider, Gray was not burdened with the usual pressures of academic life. He didn’t have to worry about publication counts, grant applications, or review committees, and was free to pursue what he saw as the most important question of all: Are we alone? Not willing to wait for the professionals to get around to it, he came to a decision: He would search for the Wow! signal on his own.
In the first part of The Elusive Wow Gray tells the story of his 22-year quest for the Wow! signal. His first idea was to build his own radio-telescope from scratch, and point it to the celestial coordinates where the signal originated. This was not as far-fetched as it sounds: Gray had considerable experience with electronics, having built radios as a teenager. He calculated that even a relatively small dish would be sensitive enough to detect a signal as strong as the one received at Big Ear, and besides, no one else was looking! If there was a regular signal emanating from the locale of the Wow!, Gray reasoned, he might catch it.
Building the radio-telescope turned out to be more challenging than Gray had expected. At a swap meet for ham radio operators he found a 12-foot dish that had belonged to a communications tower, and a steerable mounting from a World War II-era radar set. He hauled the big loads at night to avoid the police, and then rolled the dish on its side to his home in Chicago. He tried to build a receiver and spectrometer by himself but in the end had state-of-the-art equipment donated by private companies and university labs. Beginning in 1983 and for the next fifteen years Gray’s compact radio observatory operated regularly, and sometimes continuously for months at a time. It did everything that he asked of it, but it did not find a trace of the elusive Wow!
The 25-meter radio telescope at the Oak Ridge Observatory in Massachusetts, used in Project META. In 1987 Bob Gray used the dish to search for the "Wow!" signal.
In 1987 Gray took a break from his own search and travelled to Oak Ridge Observatory near the town of Harvard, Massachusetts. It was there that Harvard physicist Paul Horowitz was running a Planetary Society-funded SETI search called META (Million channel Extra-Terrestrial Assay), using the 25 meter (84 foot) Harvard Smithsonian Radio Telescope. Horowitz agreed to hand over the controls for several days of a concerted Wow! search, and Gray set to work. The giant dish and the advanced automated controls allowed Gray to observe with a far greater sensitivity and for more extended lengths of time than the relatively simple equipment he had at home, but once again the search came up empty.
Gray’s next stop was one of the great wonders of the world of radio astronomy – the Very Large Array in the New Mexico desert. The VLA, as it is known, is not just one dish; it is a set of 27 dishes, each 25 meters (82 feet) in diameter and as high as a ten-story building. The giant antennas are not stationary but are mounted on rails, and can be arranged in different configurations depending on the needs of different types of observations. When spread most broadly, the VLA simulates a single humongous dish with a diameter of 22 miles.
To use this futuristic machine it is not enough to have the ear of a sympathetic professor such as Paul Horowitz. Competition for VLA observing time is fierce, and the only way to get it is to go through the proper official channels. So Gray (with a little help from his academic friends) submitted a proposal and, much to his surprise, was granted four hours of observation in September of 1995. He drove deep into the desert night just to be on the spot when the great dishes turned towards the Wow! locale.
When Gray returned home and analyzed the results, it seemed to him that there were indeed some unknown radio sources very close to where the Wow! had originated, but it was not clear whether they were natural or not. The difference is that natural sources are spread over a wide frequency band, whereas – so far as we know – only artificial signals are strictly narrow-band. To test this Gray returned to New Mexico for four more hours of observation in May 1996, searching the same location but at a higher frequency. The radio sources, he found, were still present, meaning that they were not limited to a narrow band and therefore almost certainly natural. The hunt continued.
The VLA after searching for the Wow! signal
A portion of the VLA in its compact "D" configuration. Nine antennas in one arm recede into the distance, while parts of the two other arms extend to the left and right. The telescope has just finished searching for the Wow signal in May 1996.
Gray’s last great effort to track down the Wow! took him all the way down under, to the island of Tasmania in southern Australia. The location was remote, but the advantages were clear: the region in the sky where the signal originated rises above the horizon for only four hours in the northern hemisphere. From Tasmania it could be observed for as many as 14 continuous hours. This is particularly important if, as Gray suspects, the signal is intermittent and can only be received once every several hours. The longer one can continuously observe, the greater the chance of receiving an intermittent signal.
The radio-telescope at the Mount Pleasant Observatory in Tasmania is 26 meters (85 feet) in diameter, similar in size to Oak Ridge dish where Paul Horowitz conducted his META search. Conveniently, the dish’s spectrometer roughly replicates the channels used in the Big Ear search, making it relatively easy to compare signals between the two. To conduct the search Gray teamed up with Simon Ellingsen, who was pursuing his own research at Mount Pleasant, but was happy to donate some observation time for the Wow! search.
In October of 1998 and March of 1999 Ellingsen pointed the big dish in the direction from whence the Wow! signal came more than two decades before. When analyzing the data, it seemed that there might be something there – a signal not quite identical to the original, but still relatively strong and unusual, and emanating from a location very close by. And so, in November of 2005 Ellingsen tried once again, observing that exact spot for another seven hours. He found much more interference than he had six years before, but no trace of the Wow! signal.
The Mount Pleasant Radio Observatory in Tasmania, Australia
The 26 meter dish used in the Wow! search is in the background.
The Elusive Wow tells the story of this quarter-century quest for the Wow! signal with clarity and humor. Personal anecdotes are interlaced with clear explanations of the characteristics of different searches and the workings of low-noise receivers and spectrum analyzers. Gray is a master at explaining the technical side of the search in a way that is accessible to non-specialists and fascinating to SETI enthusiasts.
This talent for exposition is also in evidence in the second part of the book, which takes a broader look at SETI, its history, and its prospects for success. Here Gray gives a precise survey of what scientists today know about the origins of life and the high likelihood that life exists on worlds besides our own. The presence in the universe of intelligent technological life – the only kind we can hope to detect with SETI – is more doubtful, since it arose only once on Earth, and took billions of years at that. But even here Gray is optimistic, arguing convincingly that in the billions of stars and planets that populate our galaxy there could well be many technological civilizations capable of communicating with us.
Gray did not rediscover the Wow! signal, but he has not given up on it. After all, he points out, although some consider the idea that the signal originated with extraterrestrials far-fetched, no one has yet provided a better explanation. And so, despite its elusiveness, he still considers the Wow! to be “a pretty strong tug on the cosmic fishing line,” a hint of what might be out there.
On August 15, 1977, a clear signal was received at the Big Ear radio observatory that almost certainly came from the stars. Was it a message from extraterrestrial beings, a lonely beacon from an advanced civilization light-years away? The only way to find out is to keep searching.