One of the most enduring UFO mysteries of all-time has finally been solved.
In 1977, astronomers at Ohio State University picked up a strange 72-second long signal. It was dubbed the 'Wow! signal' after team member Jerry R Ehman wrote "wow!" on the computer printout.
The signal, which appeared to come from the constellation Sagittarius, was broadcast on a frequency associated with hydrogen gas.
The astronomers had set up their equipment to look at this frequency because hydrogen is most common element in the universe, and they assumed an alien intelligence would use this same logic if they were going to communicate across the stars.
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Further attempts to locate the signal were unsuccessful. In 2016, astronomers at the Center of Planetary Science suggested a hydrogen cloud surrounding a comet could be the source of the Wow! signal.
Two comets - P/2008 Y2(Gibbs) and 266/P Christensen - are now known to have passed through the area where the signal came from on the day it was detected. They hadn't been discovered at the time.
The two comets reappeared in February 2017, and radio signals astronomers picked up from them matched the Wow! signal.
Further testing showed other comets also beam out radio signals at the same frequency as hydrogen, so while it may not have been P/2008 Y2(Gibbs) and 266/P Christensen that sent the Wow! Signal, astronomers are now certain it was definitely a comet - not E.T.
"The results of this investigation, therefore, conclude that cometary spectra are detectable at 1420 MHz and, more importantly, that the 1977 Wow! signal was a natural phenomenon from a solar system body," said Antonio Paris of the Center of Planetary Science.
Their findings have been published in Journal of the Washington Academy of Sciences.