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.

Despite the imposing task, NASA's PPO is a cheerful scientist by the name of Cassie Conley. She was part of a panel at the AAAS meeting on the search for ET, where she explained how NASA does its best to make sure that any signs of life they might detect on Mars or elsewhere didn't actually travel along with the probe. The 1967 Outer Space Treaty requires that signatories that explore space don't contaminate it. In practice, this means taking a tiered approach, with different levels of precautions depending on the mission. If you wanted to land a rover on Mercury or Io, you can basically do what you want since the conditions there are far too harsh for terrestrial life. Missions to Mars, Europa, and Enceladus require much more caution, since there's a much better chance life could exist there.

For missions that just go out into space and don't come back, the most significant precautions are taken for those that involve landing probes. These are assembled in clean rooms and sterilized by baking, but as we're learning more about extremophiles, this might not always be sufficient.

Past history hasn't been that consistent. When Spirit and Opportunity were sent to Mars, we thought there was no chance of finding life, so they didn't get heat-treated to sterilize them. To avoid contaminating Europa, the Galileo probe was sent into Jupiter. Cassini, currently orbiting Saturn, is going to be flown into the planet to eliminate the possibility of it crashing into Enceladus. It'll go through the rings to do one last experiment.

But the missions that involve returning samples (or astronauts) to Earth require the most planning and precautions. Recently, several missions have returned samples from space, including Stardust, Genesis, and Hyabusa. Upon returning, their samples have been kept in biosafety level (BSL) 4 facilities, similar to the kinds of rooms we use for studying pathogens like ebola for which there is no known cure. Sadly, these kinds of precautions haven't always been followed.

During the Apollo program, NASA spent a considerable amount of time and effort to prevent possible contamination from the moon. However, when the Apollo capsules splashed down, the astronauts, covered in moondust, went from the capsule to an inflatable boat, to a helicopter, then walked across the flight deck of the waiting ship before actually entering the quarantine facility. I think on twitter we'd call that #planningfail.