When planning the Apollo 11 mission to the Moon, NASA thought of every possible detail, including a gloomy scenario: What if astronauts left something dangerous on Earth—and alien to science—the Moon germs?
Before Apollo 11 departed, NASA could not be positive that, if bits of dust or potential microbes returned home, life on Earth would be safe. Needless to say, accidentally setting loose a lunar plague on Earth's inhabitants would have erased all the good publicity received by the Moon's landing in the first place.
Just in case, in addition to the protections they were setting up to ensure that the Moon rocks remain free of terrestrial contamination, NASA decided to establish a three-week quarantine for the Apollo 11 crew.
After arriving in Houston on July 27, 1969, Apollo 11 astronauts Neil A. Armstrong, Edwin E. "Buzz" Aldrin and Michael Collins were confined to a mobile quarantine facility.