Did you know that NASA has a Planetary Protection Officer? Well, they do, and her name is Catharine Conley.
Unfortunately, she does not have superpowers, and the planet she's in charge of protecting is Mars, not Earth. Also unfortunately, NASA seems to have ignored her during the preparation for the launch of the Curiosity lander, in the process violating its Prime Directive and possibly introducing terrestrial microbes to Mars. We just don't do a very good job of protecting planets, do we?