And he says extra-terrestrials have visited Earth on several occasions - but the alien contact has been repeatedly covered up by governments for six decades.
Dr Mitchell, 77, said during a radio interview that sources at the space agency who had had contact with aliens described the beings as 'little people who look strange to us.'
Chillingly, he claimed our technology is "not nearly as sophisticated" as theirs and "had they been hostile", he warned "we would be been gone by now".
Preductably, NASA officials were quick to play down the comments of Mitchell.
In a statement, a spokesman said: "NASA does not track UFOs. NASA is not involved in any sort of cover up about alien life on this planet or anywhere in the universe.
'Dr Mitchell is a great American, but we do not share his opinions on this issue.'
A picture of my cave
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