Is the Wow signal a sign of extraterrestrial intelligence?

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Answered by: Brendan, An Expert in the Astronomy and Space 101 Category
In August of 1977, a SETI astronomer named Jerry Ehman discovered an unusual signal while working with a radio telescope at Ohio State University. The telescope would scan the skies at night and collect data on distant radio signals. It would print the data on a piece of paper so that on the following day, researchers could peruse the results for anything interesting. The signal Ehman found one day that August was of remarkable intensity, about 30 times that of normal space. The signal appeared to come from a region near the star cluster Messier 55. Ehman and his colleagues ruled out planets, asteroids, aircraft, and ground-based transmitters as sources for the signal.

The printout from the telescope represents the signal to noise ratio alphanumerically in intervals of 12 seconds. A blank space represents a ratio between 0 and 1, a 1 between 1 and 2, and so on with alphabetical values succeeding numerical values in magnitude. The signal appears as the string "6EQUJ5" and is by far the most intense signal recorded on the printout, with a peak intensity of "U" representing a signal to noise ratio between 30 and 31. Ehman circled the signal’s intensity string on the paper and wrote "Wow!" in the left margin, and the signal has since been known as the Wow signal. The frequency of the signal – around 1420.4 Hz – was also notable. The resonant frequency of hydrogen is 1420.4 Hz, and therefore an extraterrestrial civilization could use this frequency to send a high intensity signal.

Astronomers have since attempted many times to find the Wow signal. But alas, they have never rediscovered it. In a 2001 paper in The Astrophysical Journal, Robert Gray and Kevin Marvel tested the possibility that the signal had a continuous source "which could account for the detection by occasionally brightening because of scintillation, intrinsic variability, or some other mechanism." After scanning the area from which the signal came, they concluded that "the 'Wow' was not due to a continuous source". Perhaps it was a singular event rather than a repeating signal, or if it is a repeating signal it repeats very rarely.

So how do we know that the signal does not originate from a source in Earth's orbit? Is it a satellite? A satellite is unlikely for a couple reasons. First, the frequency of 1420.4 Hz is a protected frequency, meaning satellites are not allowed to transmit at 1420.4 Hz. Even if we assume that an unknown satellite could transmit at this frequency, its location and motion would necessarily be improbably precise to produce the shape of the intensity curve.

Although the signal exhibits many of the expected characteristics of an artificial ET source, there is no evidence that it necessarily must be artificial. Ehman himself is skeptical of an intelligent ET source, stating that "there is simply too little data to draw many conclusions" and refuses to "draw vast conclusions from half-vast data". Nevertheless, he is open to the possibility that the signal is indeed a sign of extraterrestrial intelligence. For now, the source of the signal remains a mystery.

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