NASA's Office of Planetary Protection has just one officer, Catharine Conley. Her job is to ensure that nasa and other U.S. organizations that journey into space adhere to the regulations put in place by the International Outer Space Treaty of 1967, which aims to preserve scientists' ability to study other worlds in their natural states, avoid biological contamination of environments we explore and protect Earth's biosphere in case alien life exists. You could say the future of our solar system rests in her hands.

It's evident why we would want to protect Earth from alien life, but why should we care about keeping Earth's organisms off other planets?
If we want to study the potential of biology on other planets, we have to control the level of contamination. When you're doing experiments looking for life, you have to be really careful about which one you believe.

How do you ensure that there's no cross-contamination between Earth and other planets?
On the Viking missions, the landers were packaged and put inside a bioshield and baked in an oven to kill all organisms—a “full-system sterilization,” we call it. The landers remained in the bioshield until they got to Mars to prevent recontamination. It was the most stringent implementation of planetary protection that anyone has ever done because we needed to protect the life-detection instruments and protect the Mars environment in case it turned out to be habitable to Earth life.

NASA is planning to redirect an asteroid to an orbit around the moon in the 2020s. Are you worried about what astronauts may encounter there?
Small asteroids have been irradiated, baked by the sun and floating around in space for such a long time that any organisms would have died. We will still evaluate any asteroid that is proposed because we want to keep the system clean, especially if we eventually have regular commercial movement between Earth and the moon.

There are a growing number of commercial space activities. Is nasa able to regulate their level of cleanliness?
We've been spending considerable taxpayer money over the years to protect other planets from contamination. Now we're in the process of figuring out how the U.S. can have an appropriate level of visibility into what our nongovernmental groups are doing. In a situation in which nasa isn't providing support, who's responsible for oversight is currently open.

Will we need a new law to regulate these groups?
We have to consider that. The Federal Aviation Administration already has authority over launches and landings, so we can regulate activities within the atmosphere, and nasa has a framework for providing input into the faa process. But we're not a regulatory agency.

There are plans for nongovernmental manned missions to Mars in the next few decades. That must create a new set of problems in terms of protecting the Red Planet.
Absolutely. Will the humans be alive by the time they get to Mars? If they die on Mars, are they then contaminating the surface? [Such events could] interfere with future science.

It seems that your office's goals are less about protecting planets from humans and more about protecting planets for humans.
The purpose is explicitly to protect the activities that humans want to do. Initially that would be science, but other things will be done in the future as well. If you wanted to drill into an aquifer on Mars, it would be in the interest of future colonists that you keep the drilling clean because organisms can grow in the aquifer and change the conditions so that it is no longer available. We've seen that happen on Earth. That would be really unfortunate.