A veteran of the Apollo 14 mission, Mitchell also says world governments are aware of the alien visits, but have covered them up.
NASA denies it is involved in an alien conspiracy or cover up.
Here's more of the story in Dr. Mitchell's own words from Reuters News.
Let's set aside for today whether you or I think extraterrestrials have already visited Earth. We won't solve anything with opinion and we are still short of irrefutable proof more than 60 years since the modern flying saucer era began on 24 June, 1947 near Mt. Rainier, Washington, just a few miles south of where I am sitting right now.
Here's the question on my mind today. Why would he lie? What explanation can there be for an American hero, one of only twelve humans to have ever walked on the moon, to make up stories like this? Would he really risk his reputation - his legacy - on a hoax? What do you think?