For decades we’ve been listening out for a message from space. Organisations like Seti analyse unusual radio signals to catch potential transmissions from an intelligent alien civilisation. But what would happen if they really heard one?

Nearly 40 years ago, radio astronomer Jerry Ehman was scanning a part of the sky hoping to detect a signal from an alien civilisation. All of a sudden, he picked something up. The signal was incredibly short, just a burst, but it registered as a distinct spike – a sort of momentary broadcast. On a print-out, he circled the blip in red pen and wrote one word: “Wow!”.

The “Wow! signal”, as it became known, has never been explained, and nothing quite like it has ever been heard again. But an organisation called the Search for Extraterrestrial Intelligence (Seti) Institute has continued listening for signals that might be created by intelligent life forms out there in the galaxy and beyond.

What would happen if Seti heard such a signal? How would it confirm the broadcast really was sent to us by aliens? A new Science Channel documentary has explained how astronauts on the Apollo 10 mission heard strange “space music” in their earphones when orbiting the far side of the moon. Many scientists believe the cause to simply be radio interference. However, the episode has raised the question of how we are able to distinguish one space sound from another in our search for a sign of life.

“Hearing something and discounting it is highly regular,” says Dr John Elliott at Leeds Beckett University in the UK. “Stuff that gets to the Post-detection Task Group is rare.”

Seti’s Post-detection Task Group is a small council of scientists primed to analyse interesting radio signals detected by radio telescopes around the world. Dr Elliott is a member – and he has spent a lot of time thinking about what would happen if we ever did hear an alien broadcast.

He’s been involved with the organisation since 1999, he says, and in that time the task group has only had to evaluate one signal every couple of years or so. There are many other detections daily, but they are quickly discounted as interference or man-made signals. Reports could come from anywhere. There is even a network of volunteers with their own receivers, called the Seti League, keeping an ear out for evidence.

It’s unlikely we’d know what aliens were actually saying to us immediately

“If there’s a repeating pattern in there, that would be of high interest,” explains Elliott. “We would ask, does that repeating pattern demonstrate a complexity that would be akin to someone sending me a language, or mathematics, or something with information in it.”

It’s unlikely we’d know what aliens were actually saying to us immediately – but we might be able to work out that they were saying something.

Seti keeps a list of “candidate signals” and there is even a system known as the Rio Scale  for classifying the significance of any signal. The ranking is based on a signal’s characteristics, how it was detected and from where it originated.

The Apollo 10 astronauts kept the “space music” that they heard to themselves for many years. In fact, their experience was only made public very recently, in 2008, when recordings of the incident were released by Nasa.

Any really interesting signals picked up by Seti would be made widely public – but not before a strict procedure of verification had been carried out. In fact, Seti has a special list of detection protocols for such an event. These involve disseminating data so that it can be analysed by third-parties. Dan Werthimer at the University of California, Berkeley – who is also a member of the Post-detection Task Group – points out that the team has to be wary of potential hoaxes.

“It might be a bug in our software or a grad student playing a prank on us so the goal is to get independent confirmation,” he says.

Interest in any potential alien signals would certainly be huge. In 2004, astronomers had to cool the hype over erroneous online reports that an “ET signal” had been discovered. And last year, Seti picked up more in a series of “fast radio burst” signals that have puzzled scientists for some time. There’s no known explanation, which has led many to wonder if the signals come from an alien civilisation.

There’s still divided opinion on what to do – Dr John Elliott

How, then, could we ever be sure? One important thing to establish would be the distance the signal has travelled. Obviously, if it’s just bounced off a satellite or space debris orbiting Earth, then it won’t be an indicator of alien communications. To do the analysis, Seti would enlist a second telescope to take its own reading.

“When you have two telescopes looking at a signal you can triangulate on it and measure its distance to figure out if it’s something nearby,” says Werthimer.

Still, there’s never yet been an urgent case.

“We’ve never had anything that we’re so excited about that we call up the director of an observatory and say, ‘We’ve got to get on the telescope now’.”

Another lingering question that Elliott and many others have considered is what would we do in terms of responding to a signal that we really did think had been created by an alien civilisation. Would we want to respond at all?

The Seti protocols state, “No response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place.”

“There’s still divided opinion on what to do – the two main camps being yes, you do respond and the other being no you don’t,” says Elliott, adding he believes that it would be a missed opportunity if we didn’t try to reply.

That, though, leaves yet another problem – how to communicate with no shared language? Elliott points out that we would have to try and establish signals for things in the universe common to both civilisations.

I think it’s going to be a while before we learn whether we’re alone or not – Dan Werthimer

“We can point to phenomena that we would know they would be witness to and use that as a key to start our dialogue,” he says.

That could mean establishing a common signal that represents “star” or “galaxy” or counting astronomical bodies, for instance. But we’d have to take into account the delay in transmissions – the nearest star system with a planet is 10.5 light years away. That’s 21 Earth years to send a message and get a reply.

Dan Werthimer says that all “interesting” signals have so far turned out to either be inexplicable, like fast-radio bursts and the Wow! signal, or simply caused by natural phenomena like supernovae.

“I’m optimistic. I think the universe is probably teeming with life, but Earthlings are just getting in the game, we’re learning how to do this,” he says.

“I think it’s going to be a while before we learn whether we’re alone or not.”

Still, there are more than enough radio signals bouncing through space to keep a check on. Someone may be out there, trying to get in touch. 

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