Interview with Chris McKay

October 1, 2005

CI: I don’t know much about your early history, how you got into astrobiology.

CM: I got interested in astrobiology when Viking landed on Mars and sent back curious results. Here were all the elements needed to support life on a planet, and no evidence of life. I got casually interested, then more engaged. It wasn’t called “astrobiology” at the time.

CI: Apart from the ambiguous results at the biological experiments, Viking dampened a lot of the frantic speculation from preceding decades because Mars suddenly seemed like a pretty dry and sterile place.

CM: It wasn’t what people thought it would be. To me that was part of the puzzle: here was evidence that Mars had water in the past. Why it was so different now? I was intrigued. A lot of people at the time were becoming less enthusiastic about Mars, but for me it was the opposite. If Viking found life and everything turned out to be just as we expected, I probably wouldn’t have gotten interested.

CI: So it was a scientific puzzle. Were you trained as a geologist or a physicist at that point?

CM: I’d been trained as a physicist, period. I did know a microbe from a planet. It was a learning experience to work with people in geology and biology.

CI: What was the career path that took you to Ames?

CM: NASA started a program called the Planetary Biology Student Intern Program, a summer program for graduate students. Somebody pointed it out to me and I applied for it that first year. I ended up at Ames, working with Jim Pollack, and after the summer they asked me if I’d come back as an NRC student. I was excited to be at Ames because that was where the Viking mission had been put together, that was the center of NASA astrobiology. That summer was a key event for me. Then I came to the University of Arizona as a post-doc working with Jim Pollack, and I’ve been at Ames ever since. As astrobiology has grown and become more popular, Ames has continued to be heavily involved.

CI: It was a great career choice, because you started as the field was maturing and it grew around you—and now you’re at the center!

CM: Exactly. It’s been fun. People used to say, “You’re crazy, being interested in this stuff.” Now everybody’s interested in it, and you’ve got to work hard to stay on the “crazy” fringe.

CI: Did you experience disincentives early in your career that made it seem like an unwise choice?

CM: I wouldn’t say disincentives, but I did get feedback from people who thought it was pointless, especially when the Mars program started warming up again. In the early eighties people would talk about what we should do on future Mars missions, and I would push searching for life—evidence of past life early in Martian history. More than once I got a lot of grief about that: “Viking did that, it’s over, we’re doing other things now and we don’t want to hear about life.” There were some strong antibodies in the system from the Viking mission, and they took a while to go away. I got arguments against making biology an important part of future Mars missions.

CI: It sounds like you have a iconoclast or contrarian streak that meant you were headed in that direction anyway.

CM: Exactly. I didn’t care that they didn’t think it was a good idea; I thought it was a good idea and I’d argue back. It’s just a question of logic. I was positive that eventually this would be what was driving not only human but robotic exploration of Mars. I felt that time was on my side, and that has proven to be the case.

CI: So you got hooked on Mars early. I’ve seen a reference to a group that you were associated with: Mars Underground. What is that?

CM: We never chose that name—it was given to us. Viking landed on Mars when I was a grad student at Colorado. A group of us formed a little study project, its actual name was the Mars Study Project. It was a four-credit class in the Department of Astrogeophysics at the University of Colorado. The purpose of the class was to look at the Mars results and think about future missions; it was what we would now call a pre-phase-A brainstorming effort—we didn’t know enough to call it that, but that’s what it was. Against the recommendation of the head of the department, our workshop invited people from all over the place to come and talk about what was important in terms of Mars research and the search for life and human exploration. Because we were grad students, we didn’t have NASA’s bureaucratic separation between robotic exploration and human exploration. For us it was a continuum of tools that one would use to address interesting topics.

We were a little bit surprised at the response to the workshop. We called it “The Case For Mars” and we accidentally tapped into a groundswell of interest in Mars that had been suppressed by the response after Viking. This was just about the time the Planetary Society was forming. There was something called the Viking Fund, which was trying to collect money to keep Viking going, as well as space-activist organizations. People were saying, “You guys have got to do it, you’ve got to build on the momentum of this great activity and form an organization.” And we, I in particular, resolved that we did not want to do that; we would be happy to discuss science and have open forum meetings and public proceedings in a scholarly way, but we were clear that we were scientists, not a public-advocacy lobby group.

As a result, Leonard David, a reporter who was involved in helping organize the conference, started calling us the Mars Underground, because we took this attitude that we didn’t want to organize or do anything official, we weren’t incorporated and had no official standing at the university—just a bunch of grad students, and happy to keep it that way. The name stuck—I guess people thought it was cute—but we never called ourselves that.

CI: You’ve been working within NASA for a long time. It’s a pretty big bureaucracy, and it’s doing excellent things in space science. Do you ever feel that the entrepreneurial route, or the privatization of space, or opening things up to the commercial sector, might lead to more rapid advances?

CM: Yes, I’m all for that. I’d be happy to have some private rocket company do launches for a tenth the cost of NASA, that would be tremendous.

CI: Do you worry that the commercial drivers of privatized space would preclude doing good science?

CM: No, I see it as part of a bigger human activity in space. I don’t feel that the only thing worth doing in space is science and that the only metric of quality for space activities is how they contribute to science; on the other hand, I know that my contribution and my personal interest is in doing science. I didn’t pursue a Ph.D. in astrogeophysics with the goal of doing commercial ventures in space. I’m glad somebody’s doing it, but it’s not my passion. People get those confused, they think that because their personal interest is science, the only thing worth doing is science, and anything in space that doesn’t maximize our contribution to science is somehow not worth doing. That’s a mistaken view. Science is for humans; science is not an end, it’s a means to an end.

CI: It’s also possible that space tourism and all sorts of things will start to take precedence. I made a graph for a class I taught, plotting the average cost of space missions overall versus the average cost of a Hollywood movie, and they crossed going in opposite directions about seven years ago. If you call space “entertainment,” then there’s a big market.

CM: Those things will happen, and I’m happy that they will happen, but I don’t want to spend my time doing space tourism. That’s not my personal interest. It seems hard to get the point across that the world is bigger than just science, bigger than just one individual’s personal interest. I’m not quite sure why.

CI: When you give public talks, you must tap into the intense interest of the public in Mars, in life beyond Earth and so on. Do you feel a broad sense of support for the things you do, that people in general think this is a valuable activity?

CM: Definitely, especially when I say we’re out to answer these fundamental scientific questions: Is there another type of life? Did life occur twice in our Solar System? Can we find evidence of it on other planets, can we study it, can we learn how it works and compare it to life on Earth? Can we understand the history and geology of this other planet, Mars, which is different from and yet similar to Earth? People understand right away why that’s interesting and useful. It’s an easy sell.

CI: Let’s get to Mars. What have we learned about the history of Mars and how terrestrial planets can evolve? And what about the current state? We’re planning for sample-return and an ambitious new wave of missions. Is there a real prospect of existing microbial activity, and could we find it?

CM: It’s hard to say. In broad brush, what we’ve learned from Mars and the fleet of Martian missions now is that there was water activity, a lot of it, and it extended until surprisingly recently. But the planet as a whole was a dry, cold world, so the water activity was localized. I like to say it’s a planet that had rivers and lakes, but no rain. This is what I call the paradox of Mars: the evidence that there was water activity—channels, extensive erosion in these localized spots—and at the same time, evidence that, viewed on large scale, the planet is basically unweathered basaltic rock, without rain.

That’s something we’re not familiar with on Earth, but it’s not completely unprecedented—we see it in the Antarctic dry valleys. I’ve been arguing for some time that what we’re learning from these missions is that even when Mars was wet, it was cold. But that’s okay—from a biological point of view, we can go to the Antarctic dry valleys and find ice-covered lakes teeming with life; not a problem. The notion that came from Viking and the optimistic interpretation of the models was that Mars had an Earth-like phase. I describe it instead as Mars having an Antarctica-like phase. The one thing it really must have had, compared to the present atmosphere, was pressure high enough that water—melting ice or melting snow—could form a stable liquid. But the general view is that Mars had water, and that the water was there for a long time.

CI: I realize it can’t be estimated accurately, but from these evocative pictures suggesting run-off, how geologically recent could that be?

CM: In localized places, some of the so-called gulley features, water could have been flowing in the current epoch, the last million years or so—essentially now.

CI: Do we know what the census of water is on Mars, compared to Earth?

CM: No, we don’t. The only direct measurements we have are the water vapor in the atmosphere—which is very small, it’s about a cubic kilometer—the water vapor in the visible polar caps, and the direct detection of ground ice by the Odyssey neutron spectrometer, which was only sensitive to the top meter. Theories based on morphology of craters suggest that there should be massive subsurface ice deeper than one meter. The ground may be ice-saturated kilometers deep. Some theorists suggest that there’s even a system of subsurface aquifers, globally connected underneath the frozen ground. But there’s no data.

CI: What melts the subsurface ice and bubbles it up to the surface?

CM: There’s a lot of debate on that. One school of thought says it’s snow melting, not subsurface water. The other school of thought says it’s water coming out of subsurface aquifers. Exactly how that water is melting and getting close enough to the surface to come out is unclear. The evidence of these gulley features is clear; the interpretation, the theory as to what causes them, is not so clear.

CI: Does geological activity play any role in water getting to the surface?

CM: Mars is geologically quiet compared to Earth, but it’s probably not extinct. The best evidence that Mars probably has some activity now is the meteorites. Martian meteorites are volcanic rock, and the age of the youngest is only one hundred and fifty million years. These rocks, which have landed on the Earth, are evidence that there was volcanism on the surface of Mars as recently as a hundred and fifty million years ago, and that volcanism was extensive enough to be a target area for an impact. It couldn’t be a tiny fraction of the surface of the planet—the odds of half of the meteorites here being that age are way too small.

CI: You’ve been heavily involved in speculating as to what Mars might have been like 3-3.5 billion years ago. What was the planet like then?

CM: Mars used to have a thick atmosphere. We infer that from the fact that it had water flowing on the surface. Let’s start with that. We have evidence that 3.5 billion years ago there was stable liquid water flowing on the surface of Mars. That’s the direct conclusion from images from the orbiting Mars Global Surveyor. For that to be the case, Mars must have had a thicker atmosphere to stabilize that liquid. Mars now is close to the pressure at which liquid doesn’t even exist thermodynamically, the way CO₂ doesn’t exist as a liquid at the surface pressure on Earth. That’s about all we can say with confidence: water on the surface and a thicker atmosphere.

I don’t think it was necessarily that much warmer than it is today. It was certainly not as warm as the mean temperature on Earth then or now. I don’t see evidence that 3.5 billion years ago there was rain, because we see surfaces that old that don’t look like they’ve been eroded. There are some mysteries, such as the northern plains—why are they so smooth? What caused that? Was there really an ocean? There may have been an ice-covered ocean at that time.

CI: What happened to the thick atmosphere?

CM: There are three ways to lose an atmosphere, and there’s debate over which one is responsible. One is the combination of a lack of plate tectonics, the formation of carbonates from the CO₂ cycle, and then the inability to recycle those carbons. In other words, the carbon gets mineralized. That’s why people have been so fascinated with trying to find carbonates on Mars. I still think that’s the best explanation.

The other explanations are more obvious ones, that Mars has lower gravity, thus loses its atmosphere to space. Depending on the model, depending on how you treat the early solar ultraviolet flux, that may or may not be an important factor as well. Another one is the lack of a magnetic field for most of Mars’s history, and the resulting impingement of the solar wind on the Martian atmosphere and the loss of CO₂ due to the solar wind. Depending on how you model the evolution of the Sun, that can be dominant for the atmosphere. All three of those factors, in relative amounts that we can’t gauge, caused the atmosphere to thin, and as the atmosphere thinned the planet got cold. More importantly, as it got cold, the hydrological cycle stopped because the liquid water phase was no longer possible, and it became the cold desert world we see today.

CI: Is it possible that 3.5 billion years ago, given what we know about extremophiles on Earth, Mars and Earth were equally habitable?

CM: I think we could say that. In fact, looking back earlier in history to 4.5 billion years ago, Mars may have been more habitable. Earth was experiencing the catastrophic Moon-forming event; it would not have been a good place. Mars didn’t seem to have such a catastrophic early event. So there was a time when Mars was the better place to live.

CI: The presumptions about how long it takes to evolve complex life are always patterned on the only example we know. But I know you’ve made arguments that it could happen much faster.

CM: The conventional wisdom—not my idea—is that complex life arises in response to oxygen; so the timing of the Cambrian explosion is a result of the rise of oxygen. If that’s true, it’s a powerful handle on this biological event, the development of complexity. It says that if you can look at the geophysical problem of oxygen rising, then you can deduce information about complexity. There’s not a hundred percent agreement among paleontologists that oxygen and complexity have a causal connection, but it’s the dominant opinion.

CI: Didn’t oxygen-producing microbes exist several hundred million years before the oxygen content started rising?

CM: Yes. So the hypothesis hangs together. Photosynthetic algae develop—they make oxygen—and they eventually titrate out all the reductives in the atmosphere, so the atmosphere and the ocean system become oxygen-rich. That allows for the development of complex life, because of the energetic efficiency of oxygen. If you accept that hypothesis, you can then ask, “Could there be complex life on Mars?” That question’s hard to answer, but you can turn it around and ask, “Could there be oxygen on Mars?” or, “What are the geophysical factors that create oxygen?” Well, it’s simple, it’s just biology. The reason it took so long on Earth was not because biology wasn’t making it, but because the Earth was so good at getting rid of it—recycling it, bringing up reducing sediments.

An active planet like the Earth is hard to pollute. If you think of oxygen as pollution, you realize that it took life a long time to overwhelm the natural recycling and cleansing mechanisms of Earth. But on a planet like Mars, it wouldn’t be as hard. The same biological production rate on Mars as on Earth would produce oxygen in the atmosphere orders of magnitude faster on Mars than it would on Earth. I did a calculation of it, and concluded that it could be as much as a thousand times faster. In that case, you could speculate that oxygen levels and complexity of life on Mars could have arisen on a time scale of millions of years instead of billions.

CI: And we have such a potential abundance of terrestrial planets out there that if something like that could happen, it probably did happen.

CM: Exactly. So we have to be careful when we take Earth’s history as the literal gospel truth of how life evolved. With complexity, we have a mechanism for timing. We don’t have such a mechanism for the origin of life, and we don’t have such a mechanism for the origin of intelligence—the other two big events in the history of life on Earth—but we do have a handle on the origin of complexity, and we can extrapolate from that.

CI: I’ve seen arguments that plate tectonics played a pivotal role in the evolution of atmospheres and the development of life—what’s your thought on that?

CM: Peter Ward and Don Brownlee, in their book Rare Earth, make the best summary of the arguments for this. The Earth’s habitability over billions of years was maintained by plate tectonics. The history of this idea is interesting. In the sixties, Sagan and Mullen published a paper pointing out the young Sun paradox, which is: “How could the Earth have been habitable 3.5 billion years ago if the Sun was so much different then than it is now?” And they said, “The gases here must have had a different composition, with a thicker, stronger greenhouse gas.”

Then Jim Lovelock said, “That’s curious, that as the Sun has changed brightness, the Earth has changed its atmospheric composition in just the right way to compensate for that. That’s too much of a coincidence.” Lovelock argued there must be a feedback mechanism, there must be a thermostat. He looked around and said, “I think the thermostat is biology,” and he coined the Gaia hypothesis. But the geophysicists, in particular Jim Walker, reacted by saying, “You’re right, there’s got to be a thermostat, but I don’t think it’s the biosphere.” He pointed out in an important paper that it was the feedback cycling of plate tectonics, and the carbon cycle, that controlled the atmosphere of the Earth. The CO₂ in the atmosphere controls the temperature, and what controls the abundance of CO₂ in the Earth is the balance between weathering and recycling in volcanoes. The carbon cycle is very temperature-dependent in the weathering-rate term. As the temperature got colder, the weathering rate would go down, so the concentration of CO₂ would go up in the atmosphere, which would tend to make it warmer. If it got warmer, the weathering rate would go up, which would draw down the CO₂ in the atmosphere. There is a temperature dependence in the carbon cycle, and particularly in the weathering rate, that tends to stabilize or buffer the Earth at temperatures near the temperatures for liquid water to exist, and that weathering requires liquid water. That was an important conceptual breakthrough, and it has made plate tectonics the dominant paradigm for how the Earth has maintained its habitability over four billion years.

CI: Since “rare Earth” became a widespread hypothesis, pieces of the argument have been deconstructed. But you think this aspect is still a strong argument?

CM: Ward and Brownlee go on to conclude that no other planet in the universe will have plate tectonics. That book has a very good introduction to habitability of the Earth, and then it draws what I think are erroneous conclusions from that. They point out how plate tectonics works and how it maintains the habitability of the Earth. And then they conclude, with essentially no additional evidence, that no other planet in the Solar System or the universe is going to have that kind of tectonic activity, so that’s all she wrote for life.

CI: Astrobiology seems littered with such situations because of the limited evidence. That must be a pitfall for everyone who works in this field.

CM: It’s easy to jump to the conclusion you want from the one data point you have and how you interpret it. For some reason, people neglect their duty to point out all the other alternatives that are consistent with the data. It does seem to be a particular danger in astrobiology.

CI: What would a “dream” NASA mission in the near future do?

CM: If the NASA administrator came to me and said, “Here’s a couple of billion dollars, do what you think is the best thing to do on Mars,” I would send a mission to the south polar region—in fact, to the crash site of the Mars Polar Lander, 76 degrees south, in that ancient ice ridge crater terrain with the crustal magnetic features. I would send a sterilized deep drill to go down into that ancient ice and bring back samples of the ancient permafrost material. Then search it, not just for fossils, but for actual preserved, frozen, dead Martian lifeforms.

CI: Given the uncertainties of subsurface water aquifers and so on, do you think the door is still ajar on continuing microbial life?

CM: It’s an open possibility that there’s a subsurface ecosystem. The problem is that if that same NASA administrator gave me those few billion dollars, I wouldn’t know where to send that mission now. I couldn’t point to a place on Mars and say, “Drill here, and we’re going to find an aquifer.” If we had evidence from ground-penetrating radar or some other tool that there was indeed an aquifer on Mars, then that would become my number-one choice. But until we have direct evidence of subsurface aquifers, I think our better bet would be to drill in the permafrost, where the water is frozen, because it’s holding a record of the early history.

CI: Scientists have been heavily primed to the possibility of frozen microbes, and the public has got some of that as well. If we got our first tangible evidence of an alternative biology, would it be a pivotal event in the consciousness of the world?

CM: I think it would be headlined, just like an ocean on Europa was headlined, but I don’t think people are going to find it a big deal. It wouldn’t be as big a deal as a space ship landing on the White House lawn, or alien invaders attacking Los Angeles. It would be a big deal in the science community because, for the first time, we would have another example of biology.

CI: And it’s either identical to ours or it’s not. Either way we’d learn something huge.

CM: Exactly. If it’s different from ours, then it’s really going to be interesting. Pick up any issue of Science or Nature and you can see that most scientists in the world are biochemists, molecular biologists who work with genes and DNA and all that stuff. Most of those scientists don’t care a whit about the space program; they’re off doing biology. If we brought back to them another example of life that was a completely different way of doing all the things life on Earth does, they would be fascinated. They might learn something that would help them in their day job, from curing cancer to controlling pests. I think the biggest impact, the revolutionary impact, would be on biological science.

CI: While we’re talking about potential biologies: you’ve also worked on Titan’s atmosphere. Apart from the fact that it pries open the idea of a habitable zone, what might we learn about the pre-biotic chemistry on Titan?

CM: It’s hard to predict what we’ll find on Titan. Here is a world with organic molecules and organic energy stored up, produced by sunlight raining down on the surface, and it has a liquid—the liquid’s not water, but it has a liquid. I think those are interesting ingredients. Maybe there could be life on Titan that is not water-based. Life on Earth would have to be described as carbon-based, water-based. You could imagine life on Titan that’s carbon-based, liquid methane-based. It’s a little bit hard to imagine because water is such a good solvent. We take it for granted, we accept the notion of the high solubility of organics and the role of water as a prerequisite for life. But we don’t know if that’s a prerequisite or if it’s just that life on Earth has taken advantage of it.

CI: There’s always a tendency to assume that Earth is the best of all possible worlds, but the parameter space of astrobiology may be larger than we imagine.

CM: Right. And the counterpoint is that just because we can’t think of how it works, we assume it can’t work. When I give a seminar and say that we might find an alternative to our type of biochemistry on Mars, somebody often raises their hand and asks, “What would that alternative biochemistry look like?” And I say, “Well, I don’t know.”

CI: It’s not invalid just because you can’t specify it. This is a field where induction is very difficult.

CM: Yes. This is not a question that will be resolved by theory. It will be resolved by observation. It would be like answering the question, “What are the New World plants like?” If you were a European scientist sitting around in pre-Columbian Europe, you couldn’t deduce from logic what the nature of New World animals and plants would be. You would have had to go there and look, and I think that’s the same for life beyond the Earth. We don’t know enough to deduce what it could be like. We have to go there and look.

CI: As an empiricist, I’m sure you’d love to have a ticket to Mars, but I know you also spend as much time as possible visiting the Mars proxies on Earth. Maybe you can talk about your fieldwork and its role in framing research on Mars.

CM: I find it useful going to places on Earth that are Mars-like, in the microbial ecology sense. The most interesting places are the dry valleys of Antarctica, which are very cold and relatively dry. And the Atacama desert, which as far as we know is the driest place on Earth—the absolute driest place, incredibly dry to the point that when I first took my instruments out and recorded two years of data, I thought something must have failed because the signal was so flat in terms of water, rain, or moisture. [Laughs] The Atacama desert is the only place on Earth where Viking could have landed, scooped up soil, and failed to find evidence of life. It would have gotten the same results: no organics, no life, but the presence of some kind of chemical reactions in the soil. Yet we know that if we walk or drive a hundred kilometers south, there are a million bacteria in a gram of soil. This core region of the Atacama desert is a little bit of Mars on Earth. In a sense, we’re hoping to understand the boundary between them.

CI: I presume our biosensors for the upcoming missions are much more sensitive, so there’s no place on Earth where they could land and not find life.

CM: The answer right now is no, they’re not more sensitive. One of the problems for Viking was that it didn’t heat the samples hot enough to look at refractory organics, it only heated up the samples to five hundred degrees. In the Atacama, we don’t see anything at five hundred degrees, all the volatile organics are gone; we have to heat it up to seven hundred and fifty. Several of us on the Atacama team are part of the instrument team for the next generation of organic analysis. We’re trying to push for capabilities that would at least be able to detect what we see in the Atacama. That doesn’t guarantee that we’ll find something on Mars, but we want to up the capabilities compared to Viking.

CI: I guess it’s not just a problem of detectability. It’s also, as with Viking, whether the evidence you get is unambiguous.

CM: Yes. There are oxidants in the soil that can mimic biology.

CI: It sounds like this fieldwork is a pacing item on preparing for these upcoming missions.

CM: That’s the way we view it. If you don’t know how to do it in the Atacama desert, if you can’t identify the oxidants, if you can’t detect the organics there, then you’re not going to do it on Mars. The converse isn’t necessarily true: just because you can do it in the Atacama doesn’t guarantee it’ll be a success on Mars.

CI: The stakes are getting pretty high. In the upcoming fleet of Mars missions, which is the one that will have the most sophisticated biogenic experiments?

CM: In the U.S. it’s the Mars Science Laboratory, which is being finished, the instruments have been selected. It will have a gas chromatic mass spectrometer. That’s got the best capability. The Europeans have a mission called ExoMars, which will also have some organic capability. Those instruments will be the next chance we have to analyze samples on Mars for organics. Both the European team and the U.S. team are pushing hard to use the Atacama experience to learn how to do that right.

Another issue in addition to temperature is the use of pyrolysis as way of liberating organics. It’s done on spacecraft because that’s an easy instrument to build, you have an oven and you heat up the sample. On Earth that’s not how any good organic chemist would extract organics. They would use liquid extraction. We’re finding that in soils containing a lot of iron, the efficiency of liquid extraction is a thousand times higher than pyrolysis. So we’re trying to push the capabilities of these instruments so they can successfully detect something on Mars as rich as the Atacama.

CI: Do any of these instruments have something like Polymerase Chain Reaction so they can replicate pieces of DNA and see what’s there?

CM: None of them do. I would like eventually to do something like that, even though in my heart of hearts I hope it would fail. I’d hope that if there’s life on Mars, it doesn’t amplify with PCR. Because if it does, then it’s just the same as us. But PCR is so sensitive that we can’t move forward without having done that. We’ve got to deploy it on Mars in any serious biological search.

CI: I also read that you go to Siberia or Mongolia. You seem to like isolated places—what’s particular about that type of setting?

CM: The interesting thing in Siberia and also in the Canadian Arctic is the old ice. If I could do a mission to Mars, I would drill down into the ancient ice and look for organisms preserved there. The Earth-based lesson for that comes from Siberia and the Canadian Arctic, and also now more recently in the Antarctic, where we find ancient ice. And in that ancient ice, we find organisms preserved. Now on Earth “ancient” means three million years or eight million years; on Mars “ancient” means three billion years, so it’s a lot longer. But we take what we can get on Earth and we study the survival of organisms in Earth ice, and then try to extrapolate to Mars.

CI: Which of these very remote places is the most challenging to work in?

CM: The most challenging physically to work in is Siberia.

CI: More than the Antarctic?

CM: Yeah, more challenging. The Antarctic is rather easy going because we have such good support—the equipment’s good, the support’s good, the helicopters fly on time. The U.S. has this incredible infrastructure working in the Antarctic. When we work in Siberia, the Russians have much less capability.

CI: You’re on your own.

CM: Yes. The last time I went, I brought $9,900 in hundred-dollar bills in my shoes so I could help them pay for helicopter time, so we didn’t have to walk to the field. It’s challenging, not because of the environment but because of the sociology. Wherever there are people, it’s more challenging because you have to interact with them. In Antarctica there’s nobody and we have excellent support from the NSF program; it’s quite easy to work there. Often when I’m working someplace else I think, “Boy, I wish we had the kind of support we get in Antarctica!”

CI: It sounds like you handle the physical side pretty easily. Have you ever had any difficult or dangerous experiences in the field?

CM: We’ve had our share of close calls. I have to admit I’m very, very careful—careful to the point of being a real chicken, because the last thing I want to do is fall off a cliff or die in a diving accident in the middle of nowhere. We’ve never had serious injuries on our field trips because we are so careful. There have been a few times where I think, “Boy, if that had been just a little bit worse, there could have been trouble”—a dive tank bursting open underwater, some equipment rolling down a ramp towards people but missing them. There’s been stuff like that, but we’ve been lucky and careful.

CI: Do you go out every year?

CM: Several times a year. In fact, if I didn’t say no, I’d be gone continuously. Between the summers in Antarctica, Boreal summer in the Arctic, fieldwork in the Atacama, the work we’re now doing in Africa—it’s like going to conferences, you could easily string together so many trips that you did only that. What I have to do is not go on every trip that our project supports. We have a team working in the Arctic, and I’ve just had to say “no” the last few summers. I went up there the summer before, but this summer and last summer I turned it down because I went to the Antarctic for a month, and I was doing fieldwork in the Atacama, and at some point you do have to stay home and write up the results.

CI: Most of us live our professional scientific lives endlessly distracted by e-mails and colleagues good or bad, and general interruptions. Do you find it a fruitful way to think more deeply about your subject when you’re out in the wild?

CM: Yes, but not so much because I’m cut off from e-mail. One of the things I really like about fieldwork, and you probably get the same thing observing at telescopes, is that you have all these scientists who come together, so we’re all out in the middle of nowhere sitting around the campfire or sitting around the dinner table and we have such excellent discussions. We’re all focused on this particular problem, this ecosystem, and we’re getting results we’ve never had an opportunity to share. We basically have mini-workshops out there in the field. I find it incredibly stimulating and enjoyable, and that’s where we make most of our breakthroughs in understanding, sitting out there in the field, talking about it.

CI: It’s a weird connection, but you’re reminding me of Heisenberg’s autobiography, where he described how the theory of quantum physics emerged in a series of walks in the woods by people like Bohr and Heisenberg and Born and so on, and how that quiet solitude, isolation, and close proximity to other smart people just talking about one thing was what broke the log jam and got all the ideas flowing.

CM: It’s really fun. I had my first experience of that working in Antarctica when I was a grad student, being in the bio lab there, with all these different teams doing different things. It was so stimulating. In addition to enjoying fieldwork, I like that aspect of it.

CI: I wanted to finish with Mars. You’ve alluded to the issue of robotic missions, but we also have the eight-hundred-pound gorilla of a manned mission to Mars on the table. Where do you stand in the debate that’s played out in the space community for decades over manned versus unmanned missions?

CM: I think it’s a false debate. Especially the way the science community likes to set it: “Science is obviously the metric, and human missions should be judged by how they contribute to science.” I think that’s a category mistake. Science is not the metric of all human activity. Instead we should be asking, “How can science contribute to the human understanding and the human experience of our world and of our universe?” By my view, exploration by actual humans is part of that human experience; it is an end in itself. Of course one of the things that humans will do is science, but we don’t exist to do science. When that debate comes up, I basically say that I don’t accept the terms of the debate, which is usually cast as: how much science do you get per robotic mission per dollar and how much science do you get per human mission per dollar: ipso facto, there’s your answer. That’s the wrong approach. The sum total of human existence is not to contribute to science, it’s the other way around. Science is part of the contribution to the sum total of human existence.

CI: Beyond a sample-return mission and a manned mission, do you foresee the motivation and the will to eventually have a settlement and learn an awful lot more about that planet?

CM: I think so. I think the history of Mars exploration will follow Antarctic exploration. I don’t know when, but I think we will establish a permanent research base on Mars that will be operated somewhat like the permanent research bases in Antarctica. They’re small, people don’t live there in any real sense, they work there for a certain period of time, a year or less on Antarctica, on Mars maybe two or four years. They will go there on field assignment, and there won’t be families; there’ll be scientists and engineers doing exploration and staying for a certain amount of time.

That will probably continue for ten or maybe fifty years. The main U.S. station in Antarctica has had scientists continuously since it was established in 1955 at the beginning of the IGY. Nobody lives there in any real sense of the word, we haven’t colonized Antarctica. I wouldn’t even call it a settlement; it’s a research outpost, and I think that’s what we’re going to establish on the Moon, and that’s what we’re going to establish on Mars. With Antarctica, the motivation for establishing the base was political activity in the IGY, which was in 1957 at the height of the Cold War. We’ve learned about ozone holes, killer whales, and penguins, and science has grown as the base has grown; now that research base is operated essentially as a scientific activity. The political motivations faded long ago.

I think that will happen on Mars too. Undoubtedly right now there’s still a big political motivation for human exploration. But as that activity matures, a base is established, science returns start coming in, and people find interesting things and new results, the base will be viewed as a scientific research outpost. Graduate students will sign up to go there to do their Ph.D. thesis, just as I had two grad students do their Ph.D. in the Arctic—each of them spent, on average, about one year cumulative time up in the Arctic during their four years of graduate work.

CI: It’s a nice perspective. The visionaries have had a hard time lately. It’s been thirty-five years since we’ve been to the Moon, the space shuttle’s old and creaky, but you believe we have a future in space?

CM: Yes, absolutely. I don’t think it will be soon. It will be when the cost goes down. When a graduate student can do research on Mars as part of his or her thesis, it’ll mean that the cost for transportation and support there will have gone down by maybe an order of magnitude. Maybe in thirty years, maybe in a hundred years. You could say, “What’s the rush?” For me, the rush is that I’d like to see it.