Astrobiology Magazine: NASA's long-range plans call for sending a human mission to Mars some time later this century. It seems likely that the most interesting places to go would be where scientists thought there was a possibility of finding life. But just by growing food, breathing and excreting, humans would produce a lot of contamination. So if safeguarding possible life on Mars is a goal of planetary protection, how could humans ever be allowed to go there?

Cassie Conley: There's actually been quite a bit of work done on this over the past 8 or 10 years within the planetary protection community, trying to figure out how it would be possible to let humans go to Mars. There is an international effort in planetary protection to try and figure out how we could send them.

The proposal is that, since we know that there are many regions on Mars where contamination from Earth is not going to be able to survive if it's left on the surface, we will allow humans to go to carefully selected spots that we acknowledge are contaminated, but are restricted such that you're not going to get winds blowing the contamination from the acceptable spots to the special regions, or have other modes of transport that might spread the contamination.

So when humans are going to go to Mars - not before, but when humans are going to go to Mars - we will allow small local regions, carefully selected regions of Mars to become somewhat contaminated with associated human commensal organisms, and organisms required for food growth.

We know that it's impossible to sterilize a human and still have the human be alive, given that humans are obligately required to have commensal organisms. It would kind of defeat the purpose to send a dead human to Mars. So we know that we're going to have to allow some level of contamination. But we're going to do it in such a way as to minimize the impact to Mars.

Any time you want to collect a sample from a special region, you will have to send a sterilized robot to that special region, have it bring the sample back and then give it to the human. But if the human is teleoperating the robot from Mars, that's still a lot better than the teleoperation that we're doing from Earth with the rovers that we have now on Mars. AM: Does that mean the human habitation site will have to have the equivalent of a JPL clean room?

CC: Yes, there will be facilities where the robots are allowed to go in one side, and the humans are allowed to go in the other side. Those specifics haven't been decided yet, but it's certainly true that you're not going to allow a sterile robot to wander into the human habitat and then imagine that it would be sterile after it did that.

There definitely will be levels of containment, so the robot can only be in the sterile region, and then there will be some kind of facility where it does the pass-off to the less sterile, the more contaminated region, where the humans are.

In fact, I believe part of the protocol that's been set up is to have the initial screening of the sample somewhere that's not near the human habitation, because you don't want backwards contamination, you don't want some martian microbe infecting the astronauts that go to Mars. So there's going to be a number of levels of containment where you test the samples progressively before you decide they're safe enough to allow humans to get at them in person.

AM: When people talk about sending humans to Mars, one of the arguments they make is that a geologist or a biologist walking around on Mars could notice all kinds of things that a robot would never discover. If you're going to fly all the way to Mars and never let the humans go where the good stuff is, what's the point?

CC: There's lots of interesting things that humans could do in appropriately contained spaces, walking around in non-special regions. There's an enormous amount of geology and other planetary science that we can do on the surface of Mars with humans instead of robots that don't involve investigating the special regions.

What we're protecting are the current special regions; we're not protecting places that might have had life 4 billion years ago. Finding fossil life from 4 billion years ago is something that would be absolutely thrilling to any scientist who wants to go to Mars - and, hopefully, to a lot of people back on Earth, too, since they paid for it.

AM: Does the moon have the same restrictions as Mars?

CC: No, the moon as a planetary body is considered Category 1, which is for places that we're really not worried about. Basically, if somebody from NASA sends me a letter saying they want to go, I write them back a letter saying okay, fine. There's some degree of documentation required of what they're taking with them, but it's pretty much a rubber stamp.

AM: So we can mess up the moon as much as we want?

CC: The COSPAR (Committee on Space Research) Panel on Planetary Protection currently considers the moon Category 1. There is some discussion that, perhaps, certain regions of the moon ought to be considered special. For example, the volatile deposits: where the sun never shines, there are these chunks of what people hope is water ice. It may be some other kind of deposit, but there are quite likely volatile materials in the very, very cold regions at the poles that might have organic material in them, which potentially would be of interest to science. So they may be declared by COSPAR to be special regions that would require additional care when studying them. But most of the moon is Category 1 and you can go there and more or less do whatever you want.

That's what makes it so good in terms of developing habitats for Mars. The moon is a completely sterile location. You can bring a habitat there, and start out knowing that it is completely sterile, and then measure the amount of contamination that is produced by the humans. That makes it incredibly valuable because you can't go to Mars until you can document that you can maintain low levels of contamination being released from your habitat.

AM: Is there a push to make planetary protection for the moon more stringent than what is strictly required by COSPAR?

CC: The planetary protection subcommittee of the NASA Advisory Council has made strong suggestions that we should consider planetary protection requirements when building lunar habitats, and using moon buggies and building lunar space suits. A lot of research is being done on how spacesuits, in particular, spread contamination, because in the air that gets released there's going to be microbes. If you build a set of habitations for the moon, all of these facilities and all of these technologies, and you don't worry about contamination, you can't take them to Mars, because they will undoubtedly be spewing more contamination than will be allowed.

+ Keeping It Clean: Interview with Cassie Conley, Part I
+ Containing ET: Interview with Cassie Conley, Part II

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