In 1977, an astronomer looking for alien life in the nigh sky above Ohio spotted a powerful radio signal so strong that he excitedly wrote 'Wow!' next to his data.

The 72-second blast, spotted by Dr Jerry Ehman through a radio telescope, came from Sagittarius but matched no known celestial object.

Conspiracy theorists have since claimed that the 'Wow! signal', which was 30 times stronger than background radiation, was a message from intelligent extraterrestrials.

But a researcher has now found that the signal, which has perplexed scientists for 40 years, was in fact just the trace of two comets as they shot past Earth.

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The Wow! signal was detected by a radio telescope in Ohio in 1977 as a 72 second-long burst of powerful radio waves during a project searching for alien signals. It earned its name after astronomer Dr Jerry Ehman circled the signal data and wrote' Wow!' in the margin (pictured)

THE STORY OF THE 'WOW!' SIGNAL The Wow! signal was detected on 15 August 1977 with a radio telescope known as Big Ears at the Ohio State University Radio Observatory in Delaware. Dr Ehman, who had been working on a project for the Search for Extraterrestrial Intelligence (SETI) Institute, noticed the surprisingly strong signal in a column of alphanumerical data. With a red pen he scrawled the word 'Wow!' in the margin and circled the sequence. Astronomers ruled out that the signal came from Earth and could find nothing in our solar system to have produced it. It is thought to have come from a region of space to the northwest of the globular galaxy cluster M55 in the constellation Sagittarius. Although Dr Ehman himself has remained sceptical, the signal has led to claims that it may have been a radio beacon or broadcast coming from far beyond our own solar system. Advertisement

Professor Antonio Paris, an astronomer at St Petersburg College in Florida, has spent the past year investigating the bizarre signal.

Using celestial records he found that two comets, unknown to scientists at the time, were passing by Earth on August 15, 1977 - the night the Wow! signal was detected.

Those comets were discovered in 2006, and last year Professor Paris suggested that a cloud of hydrogen gas in the wake of the celestial objects triggered the signal.

But the scientist had to wait until this year, when the comets flew past Earth again as part of their synonymous six-year orbits around the sun, to prove his theory.

In a paper published in the Journal of the Washington Academy of Sciences, he has now proven once and for all that the signals were not caused by aliens.

When the comets passed by this year, the signal they produced was exactly the same as that seen in 1977.

Speaking about the theory before its confirmation, Professor Paris admitted that he had wanted to be wrong.

'There's still a bit inside of me that hopes it was aliens,' he said.

When he first published the theory last year, Professor Paris said the comets produced a cloud of hydrogen gas in their wake which released radiation.

The frequency of the signal spotted by Dr Ehman in 1977 matches the emissions produced by hydrogen atoms, he said.

The clouds of hydrogen that surrounds them as sunlight breaks up the frozen water on their surface extends millions of miles around the comets, meaning they could produce a powerful signal.

Previous research has found that two comets were in the right region of the sky at the time the signal was received. A study of the comets as they passed Earth this year has revealed that the comets gave similar radio signals to those detected in 1977 (stock image)

THEORIES FOR WHAT CAUSED THE 'WOW!' SIGNAL There have been many theories over the years for what could have been the source for the short-lived, narrow band radio signal that became known as the Wow! signal. At the time, it was seen has having all the traits of having come from a distant planet, but the inability to pick it up again has frustrated astronomers. While some have taken it to be a radio message broadcast by an alien beacon into space, others have looked for other astronomical sources. Theories have included collisions between asteroids and stars, flares from stars, merging white dwarfs and colliding neutron stars. Advertisement

'Several investigations into the "Wow!" signal have ruled out the source as terrestrial in origin or other objects such as satellites, planets and asteroids,' Professor Paris said at the time.

'From 1977 July 27 to 1977 August 15, comets 266P/Christensen and P/2008 Y2 (Gibbs) were transiting in the neighborhood of the Chi Sagittarii star group.

'Ephemerides for both comets during this orbital period placed them at the vicinity of the "Wow!" signal.

'These two comets were not detected until after 2006, therefore, the comets and their hydrogen clouds were not accounted for during the signal emission.'

The Wow! signal was detected on 15 August 1977 with a radio telescope known as Big Ears at the Ohio State University Radio Observatory in Delaware.

The Wow! signal was detected as coming from a region of space close to the M55 galaxy cluster close to the constellation Sagittarius (illustrated), but new research suggests the signal may have been produced by two comets, undiscovered at the time

THE COMETS BEHIND THE WOW! SIGNAL Comet 266P/Christensen was first discovered in 2006. It orbits the sun every 6.79 years. The closest it passes to Earth is 125 million miles. P/2008 Y2 (Gibbs) was first discovered in 2008. It passes much closer to Earth, at a distance of 61 million miles and orbits the sun every 6.8 years. Advertisement

Dr Ehman, who had been working on a project for the Search for Extraterrestrial Intelligence (SETI) Institute, noticed the surprisingly strong signal in a column of alphanumerical data.

With a red pen he scrawled the word 'Wow!' in the margin and circled the sequence.

Astronomers ruled out that the signal came from Earth and could find nothing in our solar system to have produced it.

It is thought to have come from a region of space to the northwest of the globular galaxy cluster M55 in the constellation Sagittarius.

Although Dr Ehman himself has remained sceptical, the signal has led to claims that it may have been a radio beacon or broadcast coming from far beyond our own solar system.

By training radio telescopes (Very Large Array pictured) onto the part of the sky where the signal was detected, the comet theory was confirmed as the two celestial objects passed by Earth in January 2017

Some have taken it as evidence of alien life as the frequency is widely thought to be one that could be used by extraterrestrials to communicate.

The mystery surrounding the signal has only been compounded by the inability to pick up the signal again, despite repeated attempts by increasingly more powerful radio telescopes.

However, at the time, researchers did not know of the existence of comets of 266P/Christensen and P/2008 Y2 (Gibbs). The pair was only discovered after 2006.