ARS: Do you know who your Planetary Protection Officer (PPO) is? Do you know what a PPO does? Two weeks ago, I would have answered "no" to both of those questions. Thanks to a session at the recent meeting for the American Association for the Advancement of Science (AAAS), that mystery has been cleared up. Basically, a PPO has two main jobs: to make sure that missions we send into space looking for extraterrestrial life don't end up contaminating their destinations with earthlings, and to make sure that anything we bring back to Earth doesn't accidentally end all life on Earth or turn out like the Andromeda Strain.