Astrobiology Magazine: Chris McKay of NASA Ames has proposed sending a biological experiment to Mars to see if a rose could grow in Marian soil. As the planetary protection officer, can you imagine approving an experiment like that?

Cassie Conley: That would be a lot easier to approve than it would a mission that was sending a microbial organism or ecosystem to Mars. Many plants, such as Arabidopsis and petunias - and roses - are grown in tissue culture in labs on Earth, and the only living things inside the box are the cells of the rose plant or the Arabidopsis plant.

There are no microbial contaminants. Of course when the rose is growing outside in the soil it's got all kinds of microbial contaminants. But if you wanted to send a rose that was a completely sterile monoculture, the only living thing you're sending is a rose that has cells with rose DNA in them, and there are no other cells reproducing, nobody else's DNA, in that culture system, that is something that I could envision that, with appropriate consultation with COSPAR and various other agencies, might be permitted to be flown to Mars.

You could send sterilized Arabidopsis seeds, plant them in martian soil in an appropriately contained hardware system, water them and watch them grow on Mars, if you were able to guarantee, not only when they left the Earth, but also as they went along, that you had no microbial contamination, and that you could sterilize the whole system if you were to detect microbial contamination at some point during the trip. I could envision something like that being approved.

You might even send a culture of small soil worms, nematodes, that can be grown in completely sterile conditions, where the only living things in the culture are the nematodes themselves and there's no other DNA being reproduced.

AM: What do they eat?

CC: They eat chemical soup, essentially. All of the components they need for nutrition are supplied to them as pure chemicals. This was a set of experiments that I did, developing a model system for spaceflight experimentation in low-Earth orbit. This chemical system with nematodes is a monoculture; the only living organisms are nematodes. Something like that, because it's a monoculture of multicellular organisms, which certainly wouldn't be able to survive on Mars without the shelter of the habitat we provide for them, would be much more likely to be approved, rather than a microbial organism that might be able to break out and survive on Mars.

AM: Nematodes don't have any microbes living in them?

CC: They do when they're in their natural environment, but it is possible to keep them alive without any microbial symbionts. Fruit flies that is not true, many insects required microbial symbionts, just like humans do, but for some reason, some nematodes don't.

AM: Let's look at the other side of the problem, sample. Suppose we brought back a sample from Mars that contained a form of life that we failed to detect because it was so different from Earth life that we couldn't recognize it. How do you know that once it got here, it might not start to thrive and compete with terrestrial life?

CC: Any time we bring back samples from places where there is considered to be even a remote possibility of life having developed, we are required to contain that sample at higher than the highest containment level that would ever be used on the most pathogenic Earth organism. So we're required to contain a return sample coming back from a place where there might be life at a higher level than we contained Ebola virus. That is done because we don't know. And until we are sure that there's nothing harmful in that sample, we're going to treat it as if it were extremely dangerous, more dangerous than anything we've already got on Earth. That's the conservative stance, that's the stance that planetary protection has taken.

Now, there have been samples returned to Earth that spacecraft have collected, but none of those samples have been collected from a place that we think has any potential for life. So we've collected samples of cosmic dust: cosmic dust is exposed to the radiation environment in space, and there's tons of cosmic dust that falls to Earth every year. So we're pretty sure that couldn't contain any harmful life, or we already would have experienced it. We've also returned samples from cometary tails, comet dust, and those samples, again, were considered by the best experts on the planetary protection subcommittee of the NASA Advisory Council, to be sufficiently unlikely to contain life that we're not going to worry about it.

We actually had the National Research Council of the National Academies of Science put together a report advising NASA planetary protection on how to treat samples from small solar system bodies, which involves a set of questions you should ask when you consider whether a sample should be allowed to be unrestricted-Earth-return, or restricted and contained at the highest level. Samples from Mars would be contained, but samples from Mars's moon Phobos would probably not need to be contained, because it's unlikely that life ever evolved or originated on Phobos. The sample return that Russia is proposing from Phobos will require the Russian planetary protection people to perform a careful analysis of whether that sample needs to be contained or not.

AM: You mentioned that a sample returned from Mars would have to be restricted to a high-level containment facility. Does such a facility exist?

CC: We have no containment facilities yet built for a restricted sample that might be returned to Earth. Building those facilities would require quite a lot of money, and they really should be put in progress about 10 years before you actually plan to get a sample back that would be restricted-Earth-return. So starting that process is a rather large investment, and with all the budgetary constraints and the other constraints that are imposed on us at the moment, we don't really expect to have any rapid progress in building a sample-return facility.

AM: Back in the late 1990s, when NASA had plans to do a sample return in 2008, was the agency getting ready to build one of these facilities?

CC: They were, indeed. In fact, we had contracts put out to several different corporations that build bio-containment facilities for disease, to put together proposals and give us ideas as to what they would do if we asked them to build a bio-containment facility for return samples. So we've been working on this for a number of decades, ever since people have started to propose sample return, we've been having workshops and putting together documents to understand what would happen to the sample when it got back.

We've actually got a full draft protocol that describes how you would go about looking life in the sample, what you would do to make sure there's not other harmful constituents in the sample, what you would have to do if you wanted to release different parts of the sample to go out to different scientists who wanted to study it, what kind a facility you need to contain it - we've done a lot of work preparing for exactly this question, because obviously a Mars sample return is something that many people have been wanting to do for a very long time.

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