In 1977, a SETI researcher working at the Big Ear radio telescope of Ohio State University heard an extremely strong signal coming from the constellation Sagittarius. The signal lasted for 72 seconds, then it was never heard from again. It was dubbed the "'Wow!' signal" after its discoverer wrote the exclamatory remark on the first paper printout of the signal.

Many researchers still believe this signal may have been our first interception of an alien broadcast. But a new theory has recently emerged which, if confirmed, could finally put to rest the mystery behind this perplexing space signal, reports New Scientist.

Antonio Paris, a professor of astronomy at St. Petersburg College in Florida, has proposed a theory that suggests the signal may have come from a passing comet, not aliens. Though the idea is not quite so romantic and exhilarating as the alien theory, it can actually be tested, and soon.

“I came across the idea when I was in my car driving and wondered if a planetary body, moving fast enough, could be the source,” explained Paris.

It just so happens that two comets, 266P/Christensen and P/2008 Y2 (Gibbs), have orbits that would have put them in position in 1977 to be the possible source of the signal. Neither of these comets had been discovered yet in 1977, so nobody thought of them until now.

When comets pass close enough to the sun, they release a lot of hydrogen, and it's possible that hydrogen being shed in this way could emit at the same wavelength as the "Wow!" signal.

Comet 266P/Christensen was scheduled to return to the same region of space as it was in 1977 on Jan. 25, 2017. Comet P/2008 Y2 (Gibbs) will return on Jan. 7, 2018. This means that scientists can re-analyze both comets to see if their hydrogen signature matches the "Wow!" signal. If one of them does, that would seemingly put the issue to rest.

There's still reason for hope, though, if you're an enthusiast of the alien theory. For a comet to emit a signal as strong as the "Wow!" signal, it would have to shed a huge amount of hydrogen. It's certainly possible, but unlikely.

“If comets were radio-bright at 21 centimeters, I would be puzzled as to why they aren’t observed more often at those wavelengths,” said James Bauer of the Jet Propulsion Laboratory in Pasadena, California.

So the comets would have to be very unusual comets indeed to explain the "Wow!" signal. We'll know soon enough.

To that end, Paris started a crowdsourcing campaign to buy a radio telescope with which to test his hypothesis. The campaign started in March, and as of April 15, it had raised $14,850 of its $16,000 goal. It is now closed.

Editor's note: This story has been updated since it was originally published in January 2016.

Bryan Nelson ( @@brynelson ) writes about everything from environmental problems here on Earth to big questions in space.

Mysterious 'Wow!' signal may finally have an explanation
The famous signal from outer space may not have been sent from aliens after all.