On Aug. 15, 1977, a signal was received from space unlike any astronomers had ever received. And then it was gone. For years some postulated that it could have been alien in origin, but now two astronomers believe that there is a more likely explanation: passing comets.
The Wow! signal, as it’s known, was detected by Ehman while he was working on a SETI project at Ohio State University’s now defunct Big Ear radio telescope. While scanning the skies for evidence of extraterrestrial radio messages, he focused on a portion of the radio spectrum that resembles hydrogen. On 15 August 1977, he documented an extraordinary 72-second sequence of unusual intensity. Intriguingly, the signal appeared to have emanated from a M55, a globular cluster located in the constellation Sagittarius.
Follow-up analyses ruled out satellite interference, or that the signal was reflected from the Earth’s surface. Naturally, some people insisted it was an extraterrestrial message, a claim that’s never been proven. (For what it’s worth, Ehman never believed it was caused by aliens.)
The only thing scientists have been able to agree on is that the signal definitely came from space. But from where? It’s a mystery that has lasted nearly 40 years. New Scientist reports the latest theory is that the signal may have been produced by comets.
According to Antonio Paris, an astronomer at St. Petersburg College in Florida, the Wow! signal could have been produced by one or two passing comets, namely 266P/Christensen and P/2008 Y2 (Gibbs). It sounds weird, but Paris says that comets are known to release considerable amounts of hydrogen when passing near the Sun. As they make their way into the inner Solar System, ultraviolet rays disturb the comet surface, releasing a cloud of hydrogen that extends like a tail for millions of kilometres. It could have been this cloud of hydrogen, says Paris, that caused the Wow! signal.
“To test his idea, Paris proposes looking at the same region of space when the comets are back,” says Emspak. “Comet 266P/Christensen will transit the region first, on 25 January 2017, then P/2008 Y2 (Gibbs), on 7 January 2018. An analysis of the hydrogen signal of the comets should reveal if he is correct.”
His research has been approved for publication in the Journal of the Washington Academy of Sciences.
So we basically have to wait a couple of years for these comets to give us the evidence we need to prove or disprove Emspak’s idea. But even now, the explanation has its critics. “If comets were radio-bright at 21 centimetres, I would be puzzled as to why they aren’t observed more often at those wavelengths,” astronomer James Bauer from the Jet Propulsion Laboratory told New Scientist.