Because we understand so little about it, there are a ton of rumors and conspiracy theories about outer space. Some people think the moon is hollow, others believe the Earth is flat, and thousands - perhaps even millions - are convinced that, somewhere out there in the universe, aliens exist.

But not all of these things are based on pure speculation. In fact, very few of them are. Most of the time, a seemingly crazy idea is put forward after something genuinely bizarre and unexplainable happens. Something like the creepy sounds heard by astronauts way back in 1969.

During the Apollo 10 mission, the crew - Thomas Stafford, John Young and Eugene Cernan - had been circumnavigating the moon when they heard what they described as a strange kind of "music" coming from the dark side of the satellite. A tape from the mission recorded the exchange the astronauts had at the time.

"You hear that? That whistling sound?" says one of the men, before mimicking the noise: "Whooooooooo!"

"That music even sounds outer spacey, doesn’t it?" he says.

He isn't the only one to hear it, either, as another astronaut then chips in, saying: "Boy, that sure is weird music."

Over the course of an hour, the crew hear the sound several times, and even comment at one point that, "We’re going to have to find out about that. Nobody will believe us."

The sounds can be heard shortly after the two-minute mark in this video:

Al Worden, a former astronaut who took part in the Apollo 15 mission, said that the noise was eerie enough to scare anybody who heard it - let alone three men who were alone in outer space.

"If I were to hear something back there . . . it would freak me out," he said. "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."

By this point, nobody had landed on the moon, either, so what was down there was really a mystery to everyone.

However, before you run off to some internet forum on the deep dark web and tell everyone you've found conclusive evidence of the existence of aliens, you might want to hear out NASA's explanation for the strange phenomenon.

A couple months after the sounds were originally heard, Neil Armstrong and Buzz Aldrin set off on their famous mission to become the first two men on the moon. However, a third man - Michael Collins - stayed in orbit while his companions made history. While up there, he said he heard the sounds too.

But, unlike his predecessors, Collins had been warned by radio technicians that the sounds were actually caused by interference between the radio in the Lunar Module and the one in the Command Module. So, it was nothing extraterrestrial, after all.

Then again, that could just be what they want you to think.

Because we understand so little about it, there are a ton of rumors and conspiracy theories about outer space. Some people think the moon is hollow, others believe the Earth is flat, and thousands - perhaps even millions - are convinced that, somewhere out there in the universe, aliens exist.

But not all of these things are based on pure speculation. In fact, very few of them are. Most of the time, a seemingly crazy idea is put forward after something genuinely bizarre and unexplainable happens. Something like the creepy sounds heard by astronauts way back in 1969.

During the Apollo 10 mission, the crew - Thomas Stafford, John Young and Eugene Cernan - had been circumnavigating the moon when they heard what they described as a strange kind of "music" coming from the dark side of the satellite. A tape from the mission recorded the exchange the astronauts had at the time.

"You hear that? That whistling sound?" says one of the men, before mimicking the noise: "Whooooooooo!"

"That music even sounds outer spacey, doesn’t it?" he says.

He isn't the only one to hear it, either, as another astronaut then chips in, saying: "Boy, that sure is weird music."

Over the course of an hour, the crew hear the sound several times, and even comment at one point that, "We’re going to have to find out about that. Nobody will believe us."

The sounds can be heard shortly after the two-minute mark in this video:

Al Worden, a former astronaut who took part in the Apollo 15 mission, said that the noise was eerie enough to scare anybody who heard it - let alone three men who were alone in outer space.

"If I were to hear something back there . . . it would freak me out," he said. "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."

By this point, nobody had landed on the moon, either, so what was down there was really a mystery to everyone.

However, before you run off to some internet forum on the deep dark web and tell everyone you've found conclusive evidence of the existence of aliens, you might want to hear out NASA's explanation for the strange phenomenon.

A couple months after the sounds were originally heard, Neil Armstrong and Buzz Aldrin set off on their famous mission to become the first two men on the moon. However, a third man - Michael Collins - stayed in orbit while his companions made history. While up there, he said he heard the sounds too.

But, unlike his predecessors, Collins had been warned by radio technicians that the sounds were actually caused by interference between the radio in the Lunar Module and the one in the Command Module. So, it was nothing extraterrestrial, after all.

Then again, that could just be what they want you to think.