Space makes “sounds” all the time—usually due to charged particles interacting with a planet’s magnetic field. In 1979, NASA’s Voyager spacecraft picked up a noise near Jupiter (video) that sounds a lot like what the Apollo 10 astronauts heard orbiting the moon. The Cassini spacecraft recorded sounds around Saturn as well, in 2002.

The thing is, the moon has neither a magnetic field nor an atmosphere meaning the radio transmissions picked up by the Apollo astronauts couldn’t have come from the moon. So it had to be aliens, right?

Not quite. Two months after Apollo 10 heard the soundsMichael Collins, the Apollo 11 astronaut who stayed in the moon’s orbit while Neil Armstrong and Buzz Aldrin touched down on its surface, heard them too. In his book Carrying the Fire: An Astronauts Journeys, he writes that NASA radio technicians told him beforehand the sounds were the result of interference between the radio in the Lunar Module and the one in the Command Module.

Still, it must have been harrowing to hear sounds of an unknown origin while far from Earth. “Had I not been warned about it, it would have scared hell out of me,” Collins wrote. “A strange noise in a strange place.”

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