There’s a reasonable explanation after all.
On 15 August 1977, nearly 40 years ago, the Big Ear radio telescope at Ohio State University picked up a mysterious signal from space. As there was no explanation for it at the time, many believed it to be an alien broadcast. Now, Antonio Paris, a professor of astronomy at St Petersburg College in Florida, says he has a more reasonable explanation to propose: a comet.
As Jerry Ehman, the astronomer who detected the signal, listened to it over the course of 72 seconds, he scribbled a note to himself on a piece of paper — Wow! — which is how it came to be known as the “Wow! signal.” The signal gained popularity as an extraterrestrial transmission since it came in at a frequency of 1420, one of the main frequencies at which hydrogen absorbs and emits light. As it is the most common element in the universe, it would be a likely candidate as an element used in a transmission.
More likely sources for the signal were a satellite or a reflected signal from Earth’s surface, but both options were ruled out because transmissions at that range are forbidden.
Paris suggests two comets as likely culprits: 266P/Christensen and P/2008 Y2 (Gibbs). “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,” he told NewScientist.
Comets, made up of ice and dust, release lots of hydrogen as they pass near the sun and heat up. Since the telescope watched a fixed area, a comet passing in front of it with its extended tail of gas and dust would have created the type of signal that was observed. By tracing these comets’ paths backwards in time, Paris says that they would have been in the right vicinity. However, neither comet was known about at the time — not until 2006, in fact — so nobody thought to consider them.
The comets will return to the same region, one in 2017 and the other in 2018, at which point an analysis of their hydrogen signals will prove or disprove his theory.
Doubt about Paris's theory stems from some researchers who don’t believe that comets release enough hydrogen to create that type of signal that was observed. James Bauer of the Jet Propulsion Laboratory in Pasadena, California, told NewScientist that “[i]f comets were radio-bright at 21 centimeters [8.2 inches], I would be puzzled as to why they aren’t observed more often at those wavelengths.”