Wow! Signal: The Greatest 'Extraterrestrial Signal Candidate' Ever Detected

On August 15, 1977, the Big Ear radio observatory at Ohio State University detected a signal that would forever change the search for extraterrestrial intelligence. Days later, astronomer Jerry R. Ehman discovered the record of the signal and was so impressed that he wrote "WOW!" next to it, essentially naming the event. It lasted only 72 seconds, but more than four decades later, the scientific community still has doubts about its origin. Was it a terrestrial creation, or did something out there try to contact us?

The Story Begins in 1959

In 1959, two physicists from Cornell University, Philip Morrison and Giuseppe Cocconi, published a study suggesting that an extraterrestrial civilization wanting to communicate by radio would probably use a frequency of 1420 megahertz, following the natural spectral line of hydrogen, the most abundant element in the universe (and, by extension, familiar to any advanced species).

Fourteen years later, with the completion of the "Ohio Sky Survey" program, Ohio State University decided to reassign its Big Ear radio observatory (decommissioned in 1998) to SETI tasks. In 1977, astronomer Jerry R. Ehman was one of the volunteers in that program, and his work focused on manual analysis of data processed with an IBM 1130 computer and a printer. At 22:16 on August 15 (02:16 UTC), Ehman discovered a signal that he could only represent in one way.

Decoding the Signal

From a technical point of view, the sequence 6EQUJ5 is not a coded message in the signal (something that has been incorrectly repeated endlessly), but rather describes variations in its intensity. The scale is easy to analyze: A blank space represents an intensity between 0 and 1, from 1 to 9 corresponds to the respective number, and for intensities of 10 and above, letters are used. The maximum peak of the Wow! signal (and, by extension, its most important element) is the letter U, with an intensity 30 times greater than the background noise.

As if that were not enough, the reported frequency (including differences in reports and the margin of error in an oscillator) was 1420.4556 +/- 0.005 MHz, remaining just above the hydrogen spectral line. Regarding its celestial location, certain characteristics in Big Ear's design prevented precise identification, since only one of its two feed horns detected the signal, and the data processing method could not determine which of the two it was. Calculations suggest two possible origins to the northwest of the globular cluster M55, in the constellation Sagittarius. The nearest star in that constellation is Tau Sagittarii, at 122 light years.

The Best Hypothesis?

So, what is the best hypothesis? The first thing to note is that all attempts to relocate something similar to the Wow! signal were in vain. At the time, Ehman believed the signal originated on Earth and "bounced" off a piece of space debris, but that is still unlikely, since the 1.420 MHz band is a protected part of the spectrum (reserved for astronomical uses), and no terrestrial transmitter can use it, although that does not rule out the possibility of a military experiment or similar. In 2016, a professor named Antonio Paris proposed that the hydrogen cloud of two comets, 266P/Christensen and 335P/Gibbs, which were in the same region of the sky, could have been the source of the Wow! signal, but both the original Big Ear team and other astronomers reject that hypothesis.

Celebrating the 35th anniversary of the Wow! signal, the Arecibo radio telescope (which will finally be dismantled after the massive damage it suffered this year) sent in 2012 a signal in the general direction of WOW!, with a total of 10,000 tweets at the request of NatGeo, using 20 times the power available in the best commercial transmitter...