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Planetary News: SETI (2001)The "Wow!" Signal Still Eludes DetectionBy Amir Alexander17 January, 2001
Whatever happened to the "Wow!" signal, the most promising transmission from space ever detected by SETI? Ever since it was recorded almost a quarter of a century ago, SETI enthusiasts have speculated about its origin and wondered whether it could be a beacon from an alien civilization. The latest attempt to relocate the signal, reported in the January 10 issue of the Astrophysical Journal, was led by longtime SETI researcher Robert Gray with funding from The Planetary Society. But although Gray and his team used the entire Very Large Array in New Mexico, and although they detected many faint objects in the signal's general vicinity, they found no trace of an alien transmission. As of now, the "Wow" signal remains as enigmatic as ever.. The most famous signal in SETI history was detected on the night of August 15, 1977 at the Ohio State University Big Ear Observatory. As on every other night, while Big Ear was searching the skies for an alien signal, its observations were being recorded on a printout sheet. A long list of letters and numbers was continuously being churned out, one long string for every one of the fifty channels scanned by the telescope. A series of characters appeared recording an unusual transmission at the frequency of channel 2: "6EQUJ5" the list read. This startled Big Ear volunteer Jerry Ehman, a professor at Franklin University in Columbus, who was monitoring the readings that night. He circled the code for later reference and added a single comment in the margins" "Wow!" The signal entered SETI lore as the "Wow!" signal. The series "6EQUJ5" described the strength of the received signal over a short time-span. In the system used at the time at Big Ear, each number from 1 to 9 represented the signal level above the background noise. In order to extend the scale, the staff added letters, with each one from A to Z representing increasingly stronger signal levels. 6EQUJ5 represented a signal that grew in strength to level "U," and then gradually subsides. In more familiar notation, the signal increased from zero to level 30 "sigmas" above the background noise, and then decreased again to zero, all in the span of 37 seconds. Two aspects of this signal immediately caught the attention of Ehman and project director John Kraus, who saw the results the following morning. First of all, 37 seconds was precisely the time it takes the Big Ear scanning beam to survey a given point in the heavens. Because of this, any signal coming from space would follow precisely the "Wow!" signal's pattern - increasing and then decreasing over 37 seconds. This practically ruled out the possibility that the signal was the result of Earthly radio interference.
Secondly, the signal was not continuous, but intermittent. Kraus and Ehman knew that, because Big Ear has two separate beams that scan the same area of the sky in succession, several minutes apart. But the signal appeared on only one of the beams and not on the other, indicating that it had been "turned off" between the two scans. A strong, focused, and intermittent signal coming from outer space: could it be that Big Ear had detected an alien signal? For a month following the discovery the Big Ear crew tried repeatedly to relocate the signal, but to no avail. In 1987 and again in 1989 Robert Gray led "Wow!" searches using the 84 foot radio telescope of the Planetary Society-funded META array at the Oak Ridge Observatory in Massachusetts, but found nothing. For his latest "Wow!" hunt Gray managed to secure the services of the entire Very Large Array in New Mexico, composed of twenty seven 25-meter dishes. This, according to Gray, was a first: "Contrary to popular belief since the movie Contact," he emphasizes, "the prestigious $80 million telescope hardly ever listens for broadcasts from the stars." During two observing sessions in 1995 and 1996 Gray and his colleague, Kevin B. Marvel, used their telescope time to investigate several scenarios. One possibility was that the "Wow!" signal in fact represents a weak but steady transmission that momentarily gained in strength due to interstellar scintillation. The high sensitivity of the VLA guaranteed that such a source would be easily detected by Gray's survey. But despite identifying several radio sources hundreds of times weaker than the "Wow!" signal in the vicinity, nothing resembling a steady transmission was found. Another scenario assumed that "Wow!" was a brief powerful signal designed to attract attention to a weaker continuous one. Such a strategy would be more energy efficient than sending a continuous powerful beacon. But again, the VLA could detect no signal even 1000 times weaker than the
Finally there is the possibility that the signal is there, but is only broadcast intermittently. Because of their limited telescope time, Gray and Marvel could only devote less than an hour to any given position. It could be that the signal is on at other times, when no one is listening. The problem is in fact unavoidable from any location in the Northern Hemisphere, since the "Wow!" locale is below the Northern horizon during most of the day. To account for that possibility, Gray joined forces with Simon Ellingsen of the University of Tasmania, who will be able to track the area for 14 hours at a time. To this day we do not know the source of the strongest and clearest signal ever to come through on a SETI search. Since it was undoubtedly artificial, and almost certainly of celestial origin, Jerry Kraus speculates that it may have come from a space probe (human space probe, that is…) that he and the Big Ear staff were not aware of. That would certainly make it an intelligent celestial signal, but not an alien one. And still, there is always the possibility that it was something else - a true signal from an alien civilization. Unless the signal is detected again, we may never know for sure. To learn more about Robert Gray's search for the "Wow!" signal, see his article in the January/February 2001 issue of The Planetary Report. |
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