Aliens astronomy Physics

Wow! mystery signal from space finally explained

Forty years ago a signal–called the Wow! signal–was obtained from space. Some speculated that it might be from an intelligent alien source. Read Wow! Communications from little green men?

Now it is argued that that it was not from little green men, but from a comet. Such is the hype around detection of a signal from aliens that common sense is ignored. Well, time, real science and cool heads have won out. The original source has been found.

Wow! mystery signal from space finally explained
Location of the two comets shown on the sky by pink ellipses. Credit: The Center for Planetary Science

The comets, P/2008 Y2(Gibbs) and 266/P Christensen, which were not known back 40 years ago when the Wow! Signal was first obtained, appeared again in the night sky from November 2016 through February of 2017.

An online news site reports from the astronomy team.1

The team reports that radio signals from 266/P Christensen matched those from the Wow! Signal 40 years ago. To verify their results, they tested readings from three other comets, as well, and found similar results. The researchers acknowledge that they cannot say with certainty that the Wow! signal was generated by 266/P Christensen, but they can say with relative assurance that it was generated by a comet.

Back in 1977, the now-dismantled Big Ear telescope was looking for alien signals, as part of the early work in the search for extraterrestrial intelligence (also known as SETI). The Telescope detected the radio burst, which the astronomer Jerry Ehman, back then, labelled “Wow!” with a red pen, because no one expected to hear anything like it. Despite searching such a signal was not found again. Without a repeat signal, it was impossible to tell what it was or where it came from.

In January (2017), Antonio Paris, an astronomer at St. Petersburg College in Florida, directed a radio telescope to point at Comet 266P/Christensen as it passed through the region of the sky where the Wow! signal was seen. The comet passed near, but not exactly, where the Wow! signal was — about 2 degrees north of the Wow! signal location.

Paris has also explored mechanisms whereby comets might emit radio signals in the 1,420-MHz range from neutral hydrogen. This is the frequency at which the Wow! signal was obtained.

Others are not so sure

Other astronomers do not believe the explanation that the signal came from a comet. One of them most notably is Jerry Ehman, who discovered the Wow! signal in 1977. He told Live Science:2

“We do not believe the two-comets theory can explain the Wow! signal.”

Yet several astronomers, including Ehman, think Paris is wrong about the comet. But Ehman isn’t convinced it’s aliens, either. There are many phenomena that show sudden appearances and disappearances of radio signals, including fast radio bursts (FRBs), which are mysterious radio bursts that generate irregular signals that last only milliseconds.

These type of signals have unknown yet astrophysical origins. However, the explanation maybe more mundane and not astrophysical in origin at all. Paris said:2

“There is some data out there to suggest the issue is at the telescope end and not the phenomenon itself.”

So it’s possible that the signal could have been caused by a glitch in the Big Ear telescope.

The other issue is the frequency of transmission. Paris said he has shown that comets can emit in that range, but Seth Shostak, a senior astronomer at the SETI Institute, is skeptical. Shostak used to study emissions from neutral hydrogen in the 1,420-MHz range, and is less sure the emission would look right. Comets may not generate enough hydrogen to make a bright enough signal like Wow!.

“I don’t think anyone ever found such emission from comets,” Shostak told Live Science.

This highlights the problem of a one-off event. Operational science depends of repeatability of events and observations. Without that it is often just conjecture about the origin of a past event. It then become historical or forensic science and that science is weak. Thus the debate continues.

The SETI scientist wants to believe it could have been from an alien intelligence because, unless there is evidence to the contrary, that is what his worldview demands. Also it is what justifies his employment at the SETI Institute.  However, Occam’s razor would indicate that it is more likely it came from a comet (or two comets) as they passed a certain location in the solar system.


  1. Bob Yirka, Wow! mystery signal from space finally explained,, June 7, 2017.
  2. Jesse Emspak, Comet Likely Didn’t Cause Bizarre ‘Wow!’ Signal (But Aliens Might Have), Live Science, June 12, 2017.

By John Gideon Hartnett

Dr John G. Hartnett is an Australian physicist and cosmologist, and a Christian with a biblical creationist worldview. He received a B.Sc. (Hons) and Ph.D. (with distinction) in Physics from The University of Western Australia, W.A., Australia. He was an Australian Research Council (ARC) Discovery Outstanding Researcher Award (DORA) fellow at the University of Adelaide, with rank of Associate Professor. Now he is retired. He has published more than 200 papers in scientific journals, book chapters and conference proceedings.