Previously unreleased recordings have revealed the crew of an Apollo space mission heard "strange, otherworldly music" on their radios while on the "dark" side of the moon.
The three astronauts experienced the weird noises for around an hour despite being out of radio contact with Earth.
Nearly 40 years passed before recordings of the incident emerged which reveal the following conversation as they debated whether or not to tell mission control.
"It sounds like, you know, outer space-type music."
"You hear that? That whistling sound? Whooooooooo!"
"Well, that sure is weird music!"
"It's unbelievable! You know?"
"Shall we tell them about it?"
"I don't know. We ought to think about it."
The Apollo 10 mission flew in 1969 two months before Apollo 11 landed man on the moon..
Apollo 15 astronaut Al Worden told the Science Channel program: "The Apollo 10 crew was very used to the kind of noise that they should be hearing. Logic tells me that if there was something recorded on there, then there was something there.
"NASA would withhold information from the public if they thought it was in the public's best interest."
The transcripts of the Apollo 10 mission were classified and remained in NASA's archives until 2008.
"You don't hear about anything like that until years after the incident occurs, and then you kind of wonder, because it's such an old memory of those things that you get concerned about if they were making something up or was there something really there? Because you never really know," Worden told The Huffington Post.
"If you're behind the moon and hear some weird noise on your radio, and you know you're blocked from the Earth, then what could you possibly think?
"We'd had a lot of incidents where guys who flew in space saw and heard things that they didn't recognize, and you wonder about all of that. I have a very open mind about what could've happened. It's somebody's hearsay evidence -- it's only a visual or audio event, which is hard to pin down. Recollection is one thing, but actual proof is something entirely different."