It is a mystery that has baffled scientists for years - but researchers now believe they have discovered where the famous alien "Wow!" signal originated from.

In August 1977, astronomers at Ohio State University recorded an unusual 72-second signal - activity so strong that team member Jerry Ehman famously scrawled "Wow!" next to the read-out.

As the Big Ear radio telescope was searching for signs of extraterrestrial intelligence, the immediate response was one of excitement.

However, the scientists could not get a repeat, and much of the science community said there was simply too little evidence to say it was proof of alien life.

It is a mystery that has perplexed the science world ever since.


Image: The team was able to test its idea when the two comets appeared again in November 2016. Pic: CPS

Now, however, researchers with the Centre of Planetary Science (CPS) have suggested a cause.

It was a comet, they report, but one that was unknown at the time of the signal. More specifically, the signal came from a hydrogen cloud accompanying the comet.

The movement of the comet would explain why the signal was not seen again, they said.

Two comets had been in the same part of the sky that the Big Ear was monitoring at the time, but had not yet been discovered in 1977.

They appeared once again between November 2016 and February of 2017, giving the researchers the chance to test their theory.

The team reports that radio signals from those comets matched those from the Wow! signal 40 years ago.

To verify their results they also tested readings from three other comets, and found similar results.

The researchers acknowledge that they cannot say with certainty that the Wow! signal was generated by those two comets, but they can say with relative certainty that it was generated by a comet of some sort.`