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.