“To be on my very first spacewalk, to be outside, and to have contamination in my suit to the point that I couldn’t see in either eye – that, I think, would cause some people to lose control.” -Chris Hadfield
Sure, you probably laughed about it when you first heard that NASA had a Planetary Protection Officer, as though Earth actually needed protection from non-existent alien invasions. Perhaps, you thought, this might have been relevant back in the 1960s, before we realized how barren the Moon was, or how woefully insufficient the Solar System is for harboring some type of doomsday, Andromeda-strain-like bacterium.
Although that NASA office is responsible for external biological threats to Earth, the main function of planetary protection is quite different: protecting other worlds from Earth. Which is to say, every time we launch a mission into deep space, we need to ensure that Earth-based life doesn’t compromise an otherwise pristine environment. There are big questions about the Solar System that we can only answer if we don’t contaminate those other worlds; one screw-up can override billions of years of natural history.