You might think that the only people who believe in aliens are forum-dwelling internet conspiracy theorists.
But it turns out a lot of Nasa astronauts also think extraterrestrials are real and that they have been in touch with humanity for a long time.
At least four celebrated spacemen have become famous for their outspoken beliefs about the existence of extraterrestrials.
Some have seen UFOs soaring through the sky, while others claim to have been tipped off about alien contact by military top brass.
Here are four Nasa astronauts who believe aliens are real.