In 1969, as Apollo 10's orbit took it to the dark side of the moon, the astronauts on board reported hearing strange “music.”
"Did you hear that whistling sound too?"
"Sounds like -- you know, outer-space type music."
"I wonder what it is."
That was the conversation between astronauts Eugene Cernan and John Young upon first hearing the strange sounds as their ship traversed the far side of the moon, completely out of contact with Earth.
The transcripts were released in 2008 after being classified for decades, and now, the audio has been made public.
"You hear that? That whistling sound? Whoooooo," says Cernan on the recording. "That sure is weird music."
Apollo 10 astronauts Eugene Cernan, Lunar Module Pilot, Thomas Stafford, Commander and John Young, Command Module Pilot are seen in this NASA photograph.
The sounds will be explored in an upcoming show on the Science Channel, called “NASA’s Unexplained Files.”
But it is not likely that alien musicians were the source of the odd sounds.
One expert on the show says the noise was likely caused by interference between the radios on the command module, the part of the spacecraft that housed all three Apollo astronauts, and the lunar module, the insect-looking ship that landed on the moon's surface.
Here's the trailer for the Science Channel show: