After forty years of speculations ranging from exotic particle decays to advanced alien civilizations, the famous 6EQUJ5 signal has now been explained, and the explanation is embarrassingly rather basic.

In August 1977, astronomers at the Big Ear observatory at Ohio State university were scanning the sky for radio signals from space. There are numerous sources of radio waves in the galaxy, and a lot of interesting science can be done using a map of the sources of radio signals. And of course many scientists believe that if alien civilizations do exist, they will be sending radio signals into space either intentionally or accidentally, and we might find evidence of their existence through their electromagnetic signals.

However on this particular night they detected something very odd. While studying the signals, astronomers suddenly detected a 72 second long burst that was several orders of magnitude stronger than anything else in the sky. It was so strong and brief that Jerry Ehman, one of the team members, immediately scrawled the word "Wow!" next to the signal on the printout.

For the next (almost) forty years astronomers and astrophysicists have studied that one short signal and tried to determine its origin. At first it was thought to be pollution from the Earth getting reflected back, but that theory was quickly disproven. Others suggested a new phenomena from a nearby planet or asteroid, but those theories also did not hold up under scrutiny. Still others started to quietly discuss the possibility that the origin of the signal was an alien civilization, but such an extreme hypothesis would only be taken seriously if all natural phenomena were first excluded.

Then about a year ago scientists at the Center of Planetary Scientist developed a new explanation that held more promise. A few years ago astronomers discovered two new comets, dubbed P/2008 Y2(Gibbs) and 266/P(Christensen), which we now know were in the region of the sky that this signal came from on that particular night. Both of these comets are producing a cloud of hydrogen gas in their tails, and coincidentally the mystery signal had the same frequency as the emissions from hydrogen gas. And since the comets were moving quickly through the sky, it would be expected that there would be a brief pulse that wouldn't reappear in future searches of that particular region of the sky.

The test of this theory came over the past winter, from November 2016 to February 2017. The same two comets were in the night sky and accessible to telescopes on Earth, and so astronomers from the CPS obtained signals from a radio telescope that was pointed at 266/P(Christensen).  What they found was a brief pulse of radio waves of the same frequency and intensity as the 6EQUJ5 signal forty years ago.

Whether the original signal was from this comet or another one cannot be proven, but it is quite clear now that it was generated by a passing comet. After forty years of study, the final explanation turned out to be rather mundane, but still quite interesting. 

Another mystery solved!