On August 15th 1977, a radio telescope located at Ohio State University detected something strange. The telescope was scanning the stars searching for possible signals from alien civilizations as part of the SETI project, and on that date it found something. The telescope recorded an incredibly strong signal appearing to come from somewhere in the direction of Sagittarius; the signal only lasted about a minute and was never detected again.

The signal was so strong that astronomer Jerry Ehman, who first spotted it, circled it in red pen and wrote "Wow!" in the margin. The "Wow! signal," as it would come to be known, became the best evidence ever obtained for extraterrestrial life.

At least, until now. One astronomer believes he's figured out what really caused the Wow! signal and—spoiler alert—it's not aliens.

The Wow! signal, spotted and annotated by astronomer Jerry Ehman. The strength of the signal ranges from 1, low, to Z, high. Ohio State University

Astronomer Antonio Paris has been studying the Wow! signal for a long time. In 2016, he released a paper along with fellow astronomer Evan Davies suggesting that the signal could have been caused by a comet orbiting in the inner solar system. Specifically, the 2016 paper identified two comets, 266P/Christensen and P/2008 Y2 (Gibbs), that were both in the area where the Wow! signal was detected.

Both of these comets have large hydrogen clouds surrounding them that could produce the kind of signal detected in 1977. Paris spent about four months in late 2016 and early 2017 with a telescope pointed at comet 266P, and found strong signals of the same type as the Wow! signal.

Paris also examined several other similar comets and found the same type of hydrogen cloud and the same type of signal, which means that even if comet 266P wasn't the specific source of the Wow! signal, another comet is most likely the culprit.

This is bad news for anyone holding out hope that the Wow! signal would be aliens, but it's a solid conclusion to one of the biggest mysteries in astronomy. Now that we know comets can create these otherworldly signals, any future signals we get will have to be vetted much more carefully.

Update: A spokesperson from the OSU Radio Observatory, where the Wow! signal was detected, has reached out to express skepticism of this discovery. Specifically, the spokesperson notes that both comet 266P and P/2008 were too far away to have caused the signal, and that there's no prior evidence suggesting that comets can create the type of signal spotted in 1977. In particular, the Wow! signal only lasted for a little over a minute, which would be unusual for a comet.

This study is far from the last word on this subject, but it does raise serious questions that future studies will have to examine. We might not be able to close the book on the Wow! signal after all, but at the very least we have new questions to ask about a mystery that has gone unsolved for four decades.

Source: The Center for Planetary Science

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