In H.G. Wells's "The War of the Worlds," Earth's unwitting defense against the Martian hordes comes in the form of pathogenic bacteria to which the invaders lack immunity.
In reality, earthlings have created an international network whose next great mission is to protect potentially fragile Martian life, should there be any, from earthly contamination.
Catharine "Cassie" Conley, the planetary protection officer at NASA -- and possessor of perhaps the coolest title in the federal government -- is in charge of that mission for the United States, and as a result is part of a small global team charged with keeping space exploration as clean as possible.
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