UFO's? Alien Extraterrestrials? Is there some THING on the Moon?

In 1971, Apollo astronaut Dr. Edgar Mitchell walked on the Moon.

Mitchell is one of only twelve humans to have explored the lunar surface.

Recently, I contacted Dr. Mitchell by email, after reading about the forthcoming fictionalized lunar mission film 'Apollo 18' -- "there's a reason we've never gone back to the moon" -- concerning what he may or may not know about an alleged alien presence.

(Meanwhile, questions have been raised about when 'Apollo 18' will be landing in theaters. Currently the film is said to be on schedule for a September 2, 2011 release date.)

Are there extraterrestrial aliens based on the Moon? And how much does NASA, or anyone else in the US government, know?