Planetary Protection is an effort to prevent inadvertent biological or organic contamination in solar system exploration. That effort cannot be perfect in actual exploration missions, but the price of not attempting it can be seen in numerous actual contamination events on Earth (e.g., kudzu and starlings in the US, Australia-released rabbits) and the more fanciful, but possibly valid, works of fiction (The War of the Worlds, The Andromeda Strain). Extraterrestrial contamination spread by Earth missions is known as forward contamination, while backward, or back contamination refers to contamination brought to Earth. Both robotic and human missions may be affected by planetary protection practices, which strive to apply the most current science to those efforts, but it is clear that those same missions may discover new information (the hope of most missions) that could argue for new and potentially altered requirements on the next mission, or on the ongoing missions themselves.
