A possible danger associated with space exploration is the possibility of contaminating the EARTH's environment with living (or toxic) material accidentally brought back from another celestial body by a spacecraft. Although it was fairly certain that the airless MOON was completely sterile, nevertheless precautions were taken to quarantine the returning ASTRONAYTS of the APOLLO 11 to 14 missions to guard against this possibility. By APOLLO 14 it had become apparent that no such threat existed in the case of the MOON, but it is by no means certain that such a hazard might not exist in the cases of spacecraft returning from VENUS or MARS.
