It may not have been Mozart, but it sure was eerie.
At least that’s how Michael Collins described the strange noises he heard while flying around the dark side of the moon in 1969 as the pilot for Apollo 11, as his fellow mission mates Neil Armstrong and Buzz Aldrin took their first steps on the lunar surface.
"There is a strange noise in my headset now, an eerie woo-woo sound," Mr. Collins wrote in his book.
But it wasn’t the first time a NASA crew had encountered the sounds. Just two months earlier, Apollo 10 astronauts Eugene Cernan and John Young marveled over the cacophony as they traversed the lunar orbit. During their mission, their spacecraft was completely cut off from any communication with Earth for an hour. Nobody could see or hear them.
Then, according to the transcript, the astronauts heard something:
Cernan: “That music even sounds outer-spacey, doesn’t it? You hear that? That whistling sound?”
Cernan: “Whooo. Say your –”
Young: "Did you hear that whistling sound too?"
Cernan: "Sounds like -- you know, outer-space type music."
Young: "I wonder what it is."
The transcripts remained secret for more than four decades, to be released only in 2008. But the otherworldly sounds were not made public until now.
According to a new Science Channel series called "NASA's Unexplained Files," the taped recordings of this moment contained "strange, otherworldly music coming through the Apollo module's radio.” It lasts for more than an hour.
The sounds had been so strange that the team wasn’t sure if they should discuss their experience with mission control.
Cernan: "You know that was funny. That's just like something from outer space, really. Who's going to believe it?"
Young: "Nobody. Shall we tell them about it?"
Cernan: "I don't know. We ought to think about it some."
Meanwhile on Earth, NASA had no idea.
But nearly half a century later, an explanation emerges.
According to space historian Andrew Chaikin on the show, the strange music was the interaction between the radios in the spacecraft.
"The radios in the two spacecraft [the lunar module and the command module] were interfering with each other,” he said. “And that was the source of the sound.”
Not everyone is on board with this answer, however. Apollo 15 astronaut Al Worden suggests on the Science Channel program show that there may have been something more.
"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," he says. "NASA would withhold information from the public if they thought it was in the public's best interest."
Since the transcripts of the Apollo 10 mission were unclassified in 2008, there has been an ongoing discussion over the possible origins of the “outer-spacy” music heard by the astronauts.
"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?” Mr. Worden told The Huffington Post. “Because you never really know.”
But Collins, in his book "Carrying the Fire: An Astronaut's Journeys,” affirms Mr. Chainkin’s explanation.
"Had I not been warned about it, it would have scared the hell out of me,” he wrote. “Fortunately the radio technicians (rather than the UFO fans) had a ready explanation for it: it was interference between the LM's and Command Module's VHF radios."
When his Apollo 11 mission landed on the moon, the noises stopped after all.