FOR OVER 40 YEARS ASTRONOMERS HAVE SOUGHT TO EXPLAIN A MYSTERIOUS ONE-OFF ‘ALIEN’ SIGNAL, BUT ARE WE NOW FINALLY CLOSE TO AN ANSWER?

REPORTED BY DAVID CROOKES

On 15 August 1977 the Big Ear radio telescope belonging to Ohio State University scanned the night sky. There was nothing unusual about this. Turned on for the first time in 1963, the telescope had long been used to search for extraterrestrial radio signals, churning out reams of computer printouts via an IBM 1130 mainframe computer that would then be looked at in fine detail by the observatory’s astronomers.

Each time someone so much as glanced at one of the jam-packed pieces of paper, they hoped to see something significant: evidence, no matter how small, that life may be out there. So when astronomer Jerry Ehman studied the data taken from that warm summer’s night a few days later, he was startled. Staring at him in a vertical line was the baffling sequence of numbers and letters ‘6EQUJ5’. ‘Wow!’ he wrote, highlighting the sequence with a circle of red ink.

Since the discovery was made, there has been much debate over the source of the signal. We know for certain that it was detected as it passed across the telescope’s field of view at 22:16 EST that night, and we know it was coming from a grouping of stars called Chi Sagittarii. We understand that it lasted for 72 seconds - and that it has never been detected since, not even in the weeks following the original discovery.

Perhaps most crucially, the frequency of this one-off signal was also very close to what is known as the 21-centimetre line, or hydrogen line. This is important because back in the 1960s and 1970s, it had been hypothesised that extraterrestrials looking to communicate would most likely use the most abundant element in the universe: hydrogen. This emits a radio frequency of 1,420MHz, which is exactly what was picked up by Big Ear.

“When this signal was detected at 1,420MHz, which indicated hydrogen being present in a part of the sky that had always been known to be quiet, it was like, ‘oh my god! It must be aliens’,” says Antonio Paris, a professor at St Petersburg College in Florida. It explains why the ‘Wow! signal’, as it quickly became known, has long been associated with the possibility that it was sent by extraterrestrial life. That it was discovered in the same year as the Hollywood releases of Close Encounters of the Third Kind and Star Wars was simply a delicious coincidence.