Before Apollo 11 set out, NASA couldn't be positive that, if bits of dust or potential microorganisms got loose back home, life on Earth would be safe. Needless to say, accidentally setting a lunar plague loose on the inhabitants of Earth would have erased all the good publicity garnered by accomplishing the
moon landing in the first place. Just in case, in addition to the protections they were establishing to make sure the moon rocks remained free of terrestrial contamination, NASA decided to establish a three-week quarantine for the crew of Apollo 11.