The list of those who subscribe to the theory that alien life forms and UFOs have visited Earth amid a massive government cover-up is long and varied. It includes cranks, paranoid delusionals, editors of the Daily Star (and sometimes all three).
But a NASA astronaut who is the sixth man to have walked upon the Moon?
The profile of Edgar Mitchell does not conform to that of your common or garden UFO aficionado. He holds two bachelor of science degrees and a doctorate in aeronautics from the prestigious and not exactly tree-huggy Massachusetts Institute of Technology.
Along with his co-astronaut Alan Shepard, he holds the record for the longest moonwalk - for nine hours on February 9 1971 as part of the Apollo 14 mission.
Put all that together and it is no wonder that an interviewer with a UK radio station almost fell off his seat this week when he lobbed Mitchell what he thought was a throwaway question: Did he believe in life on other planets?
"Oh yes," came the reply. "There's not much question at all that there is life throughout the universe. I'm totally sure we are not alone."
A deep intake of breath could be heard from the presenter for Birmingham-based Kerrang radio. But there was more. Mitchell said he had intelligence "that we have been visited on this planet and the UFO phenomenon is real - though it's been covered up by governments for the last 60 years or so".
In hindsight, there had been earlier clues that Mitchell was to become one of the most distinguished and unlikely members of the club of UFO believers that, had they been taken on board, might have made this week's revelation a little less astonishing. He has mentioned extra-terrestrial beings in obscure American outlets in the past, though never before given as much detail about his convictions.
There was his claim to the culture magazine Cabinet a few years ago that he had conducted unofficial experiments in extrasensory perception during the Apollo 14 mission, trying to make contact via telepathy with collaborators back on Earth. (The experiment failed, but let's not dwell on that.)
More recently he revealed that he had been cured of a bout of kidney cancer by a man called Adam Dreamhealer who, though based in Canada, did all his healing from a distance and managed to effect a complete recovery through the power of consciousness.
So his comment this week that Roswell, the 1947 appearance of an alien, really did happen, and his description of extraterrestrials as harmless "little people," can be seen to fall in the same tradition.
For NASA, which has been struggling in recent months with the fall-out from its female astronaut who drove across America to confront a love rival wearing a nappy, there was a tone of "here we go again" to its response. In a statement, the agency said: "Dr Mitchell is a great American, but we do not share his opinion on this issue."
