Interview with Chris Chyba
November 11, 2005
CI: I know a bit of your history, but more generally, how did you get into your field?
CC: I started out in mathematical physics at Cambridge as a Marshall scholar. I did part three of the Math Tripos on field theory and gravitation and some work in general relativity. I had a few papers in GR and realized a couple of things. One was that I was not going to see a lot of other science if I stayed on that trajectory. Also, I had a long-standing interest in foreign policy, and there was no conceivable way to get at that through a mathematical physics background.
I was frustrated in terms of wanting more breadth, and in bookstores I was spending all my time in the “origins of life” section. Planetary science seemed like a way at getting at origins of life for somebody with a physics background, so I headed in that direction. Even though there’s no obvious, direct foreign policy connection, it seemed closer than mathematical physics. Carl Sagan was one of the few people in the States doing what was then called exobiology; he had an interest in policy and arms control issues, so it seemed like a natural move for me to make.
CI: Where did you get your craving for foreign policy and public policy?
CC: I don’t have a precise answer to that, but I’d always wanted to be a scientist. I grew up in the Sixties, not that long after the Manhattan Project. There was a different model then. Black-and-white reruns of films on television presented scientists as people who were playing a part in making the world better. Even in the silly films, like monster movies, the scientist played some important role. I grew up with this sense that science was a way of understanding the world and a way of making a difference for the better.
CI: That’s interesting, because in pop culture and in those kind of movies, scientists are at the pivot of good and evil; science cuts both ways.
CC: That’s right. I know Physics Today had an article on this years ago, but I would suggest that the balance around that pivot when I was growing up had scientists working more on the side of good. It’s been something of a transition, I think the positive models were stronger when I was younger. I minored in political science in college, and I did my senior thesis in political science. So the interest was there all the way through.
CI: And your Ph.D. was in planetary science?
CC: Yes, in the Cornell astronomy department.
CI: Was Sagan your first mentor or role model? He was voracious in his interests.
CC: Carl was my thesis advisor, he was a very good friend and we remained close until his death. Carl and I had a very good, very frank relationship; we were free to disagree with one another, and did disagree about quite a few things.
CI: Was he a role model in the sense of a publicly engaged scientist, and someone who was unafraid to tackle an issue that was a consequence or an implication of silence?
CC: Absolutely. Carl made a decision not to be directly involved in government. He had been on some advisory committees early in his career and he decided that they restricted his freedom of movement. Carl was absolutely dedicated to the idea of free speech, of thinking through a topic and being utterly brave with respect to what he had to say about it. That’s enormously admirable, but I think it also has some tension with the idea of, say, working directly within the government. There are different ways of effecting change in the world; that’s one route. I have greater interest in working within the system. Carl would not have wanted to pursue that.
CI: Ann Druyan told a nice story about him in Senator Proxmire’s office, patiently debating an issue after the Golden Fleece award. He was using his personal power and charisma to engage an individual politician.
CC: He was heavily involved in the process without being inside the process. No question about it, he was quite influential.
CI: Having talked about science for good and science for evil, one of the discouraging things for scientists over the last few decades in this country is that science has sometimes seemed irrelevant in public policy. It’s been neutered in terms of access to the highest levels of the administration and bounced around like an ideological ball. Is that something that motivates you? What’s your goal in your policy work?
CC: The influence of scientists in terms of policy has been in
decline since the Kennedy administration. I see that in the evolution of the
role of the President’s science advisors. There are some powerful exceptions to
this, but the overall trend has been less influence. I see it on Capitol Hill, with
the decision in 1995 to eliminate the Office of Technology Assessment, which
was a self-lobotomy Congress performed with respect to science. These trends have
accelerated recently. I don’t see it as my job to try to solve that problem, although
it’s an important problem. I think the responsibility resides both in
I’m in a very fortunate position to have an opportunity, at whatever level, to make some impact on the human future. It would be grandiose of me to suggest it was going to be more than a very minor impact, but there’s an opportunity there, and it seems to me that I should try to make a difference for the better. Planetary exploration is one example among many of the sort of things we can do as a civilization; it represents the best that human beings can do. At the same time, we face enormous difficulties. We faced one set of difficulties last century, we face a different set this century. If I can play some role in trying to help us meet those difficulties, I’d like to do that. I’ve spent a lot of time thinking about the ocean on Europa, and the prospects for life in that ocean, which doesn’t matter much for us if human civilization continues to go to hell in a hand-basket. I’m in the happy position of spending some time on both issues.
CI: Scientists are in a strange position of thinking of processes and time scales that are completely disconnected from the time scales of politics and policy. It’s hard to present an scientific idea to a political audience when there’s not a ten year time line, but a fifty or a hundred-year time line. Global warming is the classic example, but there are others. You’ve got an enormous conceptual hurdle with people who are looking at their next election. How do scientists engage policy makers?
CC: I don’t have a general answer. There are some policy makers who
are capable of doing, and willing to do, what you’re describing, either because
they’re among the very few who are scientists—Rush Holt was a great example—or
simply because they do have some vision for the future. I think, for example,
that President Clinton had a sense that the 21st century was coming;
his overworked metaphor was “the bridge to the 21st century.” There
was a sense of trying to prepare the
Think about John Kennedy: there are the famous press conference remarks he made in 1962 looking ahead to 1975—more than a decade in the future at that point—talking about how we might be looking at a world of fifteen or twenty or twenty-five nuclear weapon states, and how that caused him great alarm. In terms of nuclear proliferation, he was thinking about what needed to be done to try to head off a world that he envisioned. There are individuals who have that kind of vision. I share your concern that too few do.
CI: Another way we impact the view of science and the process of science in public policy is through education. What are your thoughts about the state of science education?
CC: Education generally, and scientific education in particular, is enormously important. What’s challenging is that it’s only one of many things that are important. I was heartened to see an article in The New York Times saying that there’s been a substantial increase in the number of college students studying a foreign language—it’s up 17% since 1998—and a rise in language houses on campus, where people are immersed in another language when they go back to their dorm. That’s just one example. There are so many things that we need to address, and science is absolutely one of them. I don’t see how we get through this century without having a much better-educated population with respect to science, but also—this is one of the reasons it’s difficult—with respect to a lot of other things.
CI: Astrobiology is really surging; there’s an almost palpable sense of excitement as the number of extrasolar planets rises, we think we might be getting to Earths within a decade, and maybe even atmospheric diagnostics of terrestrial planets a little bit after that. What excites you about the way astrobiology has developed?
CC: Somewhere in the mid-nineties I started giving talks with the title, “The rebirth of exobiology.” Of course that word’s passé now.
CI: And it was much-lampooned by biologists at the time.
CC: George Gaylord Simpson had a famous paper in Science where he said it was a subject without a subject matter. I’d point out that the word was coined by Joshua Lederberg, who was a Nobel Prize-winning geneticist; so not all biologists lampooned it. To me it’s a strange point of view to take, since so much of what’s done in many areas of science is exactly looking for things of questionable existence. It’s not clear to me why we should respond differently when it’s biology, and not physics or material science.
You’re right that the discovery of extrasolar planets is part of this rebirth, along with the prospect that we’ll know the answer soon to a 2,500-year-old question about the existence of other Earths. Another component is the explosion in knowledge about Mars and Europa, the changing sense from the idea that liquid water might be extraordinarily rare to the notion that there might be a number of environments in the Solar System where liquid water is intermittently or constantly present—Mars, Europa, probably the sub-surface of Ganymede, Callisto. Maybe liquid water oceans are a common component of the sub-surface of most large icy moons.
There’s also the realization—it seems trite now, but when I was a grad student this was a topic of continuous debate in planetary science meetings—that organic molecules are pretty much everywhere. They’re common in the interstellar medium and they’re a common component of objects in the outer Solar System. That’s a big change. There were people yelling about this in the mid-Eighties; now everyone’s ho-hum about it—“Of course there are organics everywhere, carbon’s one of the most abundant elements, what else do you expect?” Yet for a time, it freaked people out.
The explosion in knowledge about the deep biosphere on Earth and extremophiles is another important factor. That’s partially because of what it suggests about the range of conditions under which life can survive; which is relevant to thinking about Mars. As we learn more about low-temperature organisms and the likely salt content of Mars, we’ve pushed the boundaries of habitability on Mars to the point where there may well be lots of niches that are regularly available. Those discoveries about the biosphere are also significant because they emphasize how little we know about biology on Earth. The realization that we’ve only cultured perhaps a tenth of a percent of the organisms on Earth—it’s humbling, and it suggests that there’s a lot more out there, even on our own planet, than we’ve recognized before.
None of those things demonstrates that there’s life anywhere else in the universe. It’s entirely possible that we’re it, but all of them trend in one direction, which is that things look more hopeful now than they might have looked, say, immediately after the Viking landers.
CI: How does our knowledge of extremophiles on Earth frame how we should think about habitable zones when we look beyond the Solar System?
CC: “Habitable zones” is a peculiar term and I think it’s easy to be unfair with it. I remember Jim Kasting saying to me some years ago, with some exasperation in his voice, “You know, when we gave the strict definition of habitable zones, it’s not like we didn’t know there might be sub-surface oceans on worlds like Europa.” They were trying to be precise, which was needed in the field. The idea was to have a test Earth that you could move around the Solar System the way you’d move around a test particle in a physics problem, and ask in what range of heliocentric distances a world like the Earth would be able to sustain liquid water, and so on. That concept—a world that can sustain liquid water at its surface—is still a valuable concept, but obviously that doesn’t at all define the volume in a given solar system in which life as we know it might be able to exist it.
It’s likely that there’s a fraction of the biosphere on Earth that is entirely independent of surface photosynthesis. There was probably an initial biosphere on Earth that wasn’t dependent upon photosynthesis, although that’s a little harder to demonstrate. But there’s probably a component of our biosphere now that would continue to survive if the Sun went out tomorrow. That changes the way we think about the prospects of the distribution of life in solar systems. Or for that matter, outside of solar systems—if Dave Stevenson’s ideas are right, there might be a lot of planets that have become untethered from stars, but which could nevertheless still sustain liquid water due to geothermal heating.
CI: You’re interested in Europa. Based on what we know about it
environmentally and geologically, does Europa fall within the bound of
extremophile habitats on Earth? Are analogs like
CC: Not in a strict sense. I don’t think we have an exact analog; that’s partly because we don’t know enough about the conditions in the Europan ocean to confidently make such a statement. For example, we don’t know the salt content. There’s a number in the literature that often gets cited, which is a salinity comparable to that of Earth’s oceans. But when you go deeper into the problem, there’s a range of sub-surface models in which you trade off depth of ocean and depth of the ice layer against salinity, in order to fit the observations. Without understanding things as basic as the range of possible salinity, it’s hard to point to any particular terrestrial model. Having said that, microorganisms on Earth are capable of inhabiting the entire range of salinity we know, down to extremely briny waters. Salinity alone isn’t going to rule out the prospects of habitability.
On Earth the majority of microorganisms do not depend upon molecular oxygen. There’s probably not a lot of molecular oxygen on Europa, but that’s not a showstopper. I don’t think there are any showstoppers. I think that for any hypothetical set of conditions, you could point towards an organism on Earth that in principle could live there.
However, we don’t know if there is a source of chemical disequilibrium there that could fuel the metabolism of a terrestrial microorganism. The other problem is that our understanding of the origin of life is so poor that even if life could exist in the Europan ocean now, that doesn’t mean that life could have originated in that ocean. That turns on a lot of things—whether or not solar energy is necessary for the origin of life, and the role of salinity, to name two. There are experiments at UC Santa Cruz suggesting that a number of reactions having to do with both RNA synthesis and primitive cell membrane formation are inhibited by salinity. On Earth there were a whole range of salinities to play with, presumably; on Europa, there may be only one salinity. We know so little that it’s hard to answer the question of the bottom line, but there seem to be no insurmountable barriers.
CI: What about the same question applied to sub-surface Mars, where we have more knowledge, though I don’t know how close our terrestrial analogs are. What should set our expectations, especially when biomarkers are such a tricky issue? Without sample return, do we have the prospect of identifying existing sub-surface life?
CC: I wouldn’t say that it should be there. In the absence of a better understanding of the origins of life, we can’t have that expectation. The possibility is interesting if we believe that there was primitive liquid water. Because of interplanetary transfer of microorganisms, there might be another way to have organisms on Mars, even if it turned out the origin of life didn’t take place there.
I’ve just finished chairing a committee for the National Academy of Sciences on preventing the forward contamination of Mars. We reviewed issues of potential habitability of Mars with a committee that had several Mars scientists as well as several microbiologists, and we talked about half a dozen possible habitable sites on Mars based on what we currently know. Those include periodically transient, liquid water environments in the near sub-surface—perhaps in the upper meter—over much of the surface. When you start looking at the salts that may be present, you can push liquid water down to 220 Kelvin or so. That opens up a lot of the Martian sub-surface to the possibility of permanent sub-surface aquifers, or even a complete hydrological system. The more we learn, the greater the prospects that such environments exist. I think NASA’s broadly on the right track with its exploration strategy—“follow the water.”
CI: Budgets are not looking great, and some missions are moving backwards at a rate of one year per year. If you could pick one of these future missions, which would it be? I guess Europa is barely on the manifest at this point?
CC: I chaired the science definitions team for the Europa orbiter almost a decade ago now, and in that original version we were going to be at Europa in 2003, which seemed a long way away at the time. Then we had a diversion, which I always thought was a mistake: tying the exploration of one of the highest priority objects in the Solar System to an unproven and undeveloped technology, a space nuclear reactor. Now we’re back to something called the Europa Geophysical Orbiter.
CI: You could easily have been talking about the James Webb Space Telescope, which, as the successor to Hubble Space Telescope, is an unproven and scary technology upon which we’re hanging everything.
CC: I thought the idea that Dan Goldin implemented—missions that were intended to prove technologies that could then be incorporated into exploration missions—was a wise way of proceeding. I would put Europa at the top of my list for the outer Solar System, even though it’s going to be at least ten years before we get back there. With respect to Mars, we still have a fairly ambitious exploration strategy. I was sorry about the loss of the Mars Telecommunications Orbiter, because the prospect of having routine high bandwidth returning from Mars, real-time video from the Mars Rover, would make Mars seem so real to people, particularly kids. It would have had a great psychological impact.
CI: Just the simple little web gizmos NASA put up—kids could drive the fake Rovers along pre-determined paths, with a visualization tool. That’s incredibly powerful. Teachers love that kind of capability, and it gets a huge buy-in right down to the youngest people in space science.
Let me ask about origin of life research. Compared to the breakneck pace of discovery of extrasolar planets and the exciting prospects on Mars, origin of life research seems to be in a different state. It’s never going to get easier to find old, unaltered rocks and show whether or not life started much before 3.8-3.9 billion years. It’s also difficult to simulate what happened on the primordial Earth in the lab. What do you see as the most fruitful directions in that research?
CC: Back in 1996, when I was giving “Rebirth of Exobiology” talks, a bullet on those slides would have been, “progress in origins of life research”—in particular the RNA world, which represented a step forward because it provided a credible answer to the ”which came first, proteins or DNA?” conundrum. RNA’s not prebiotic, in the sense that it almost certainly wasn’t the first self-replicating system; there has to have been some predecessor. It’s always going to be hard to know if what we’ve managed to do in the lab replicates what actually happened on Earth. The best we’ll be able to do, ultimately, may be to have several plausible and reasonably well-demonstrated pathways, but never know which of those, if any, happened historically. But knowing those pathways would be a big step forward.
I co-chaired a report for the SETI Institute on areas where one could take a big step ahead in astrobiology with the right funding, particularly private funds. One area our committee identified is combinatorial chemistry. One of the problems in prebiotic chemistry work now is this: say you’re trying to understand the catalytic role minerals may have played for the polymerization of nucleotides. You have a grad student working with one particular mineral. They take maybe a few months to test it, and if nothing interesting happens at first, you have them look at one or two other minerals. But if nothing continues to happen, you’d better get that student doing something else, because you can’t waste a year of your student’s dissertation. On the other hand, if something interesting does happen, you probably have them devote themselves entirely to that system. The result is that we explore the role of one mineral at a time, when there are thousands of minerals that are relevant, as well as a vast range of potential conditions—pH, salinity, you name it. It’s a huge search problem.
CI: And it would be nice if some of the lab work could explore alternative biologies.
CC: The problems there are even more daunting. Our report wasn’t that
ambitious, it was still working within the carbon-water paradigm. People in the
private sector are routinely working with hundreds of thousands or millions of
combinations. We spent some time at Diversa Corporation in
CI: There’s huge money to be levered. The drug companies have been far too conservative in their business model and they’re running out of antibiotics; extremophiles have already shown some really interesting capabilities. There could be a hook into the much bigger commercial arena.
CC: I agree. Diversa is dedicated to bioprospecting, and then using directed molecular evolution to try to evolve the DNA corresponding to an enzyme that may have practical utility. They are in effect doing what we’re talking about, but obviously with a different end purpose. Some biotech companies are doing this sort of thing; it’s just a question of having the resources and the time and the interest to shift to origins of life.
CI: Let me ask another big-picture question about the origin of life. Are we entitled to look at the rapidity with which life started on Earth, and the diverse evolutionary niches and robustness of extremophiles, and conclude that the formation of life, given a broadly defined habitable planet, is almost inevitable?
CC: I don’t think so. I think we’re entitled to say it can happen; that’s why questions like the time scale for the origin of life seem important to me. If there was a strong argument that life on Earth originated in less than a hundred million years—Stanley Miller would say less than ten million years—then I’d be comfortable with an argument extrapolated to another world that said, “With liquid water for a hundred million years, it’s possible that life originated.” But arguing that because it happened fast on Earth implies that it’s going to be likely…I don’t see how you get from the observation to the conclusion.
CI: Let’s move out on the tree branch to where it gets thinner. The consensus among astrobiologists seems to be that the universe is likely to be littered with habitable planets and maybe primitive microbial life forms—but when it comes to those later terms in the Drake equation, all bets are off, we have no idea how to frame probabilities. Is there a pivot in the Drake equation where we lose all traction on any kind of prediction at all?
CC: Yes. That starts to happen with the origins of life term, although we at least have some actual data there. We started funding some research in this area at the SETI Institute. We talked about trying to get some relevant knowledge for the “evolution of intelligence” term in the Drake equation by looking quantitatively at that issue on Earth, rather than having qualitative, century-old polemics on the issue. We can make progress with some of those terms.
One question we discuss in our Annual Reviews paper is, “Is there or is there not an evolutionary driver towards greater intelligence?” There’s a story you can tell for why that should be the case. But life on Earth has also gotten larger through time—does that mean that being big is selected for, or does it mean that being big is selected for sometimes and being small is selected for sometimes? If you start out really small, the only way diffusion can run is on average toward bigger organisms. Is intelligence like that, or is there a mode of selection that favors higher intelligence? Having a quantitative answer to that question will help address those later terms in the Drake equation.
CI: Is it possible to move beyond strongly-held opinions? I was reading about the debate between Simon Conway Morris and Richard Dawkins. They look at the same evidence from the history of animals over half a billion years and draw opposite conclusions on contingency and convergence.
CC: It’s possible to move beyond polemics in some well-defined, quantified areas. A paper by Lori Marino does that for one particular set of organisms; it needs to be done much more broadly. She looked at the evolution of brain size in toothed whales for the last fifty million years, and applied three different statistical tests to this question: in that group of organisms, has there been a selection for larger brain sizes, or has it been as likely in any given speciation that the brain becomes bigger or smaller? The data say that there has not been an overall driver for bigger brain sizes, that it’s been in effect a random event. That’s relevant knowledge, but humble knowledge—it doesn’t answer the big questions you and I are interested in. But science sometimes says, “We don’t claim you’re going to know a whole lot, but we can make some progress in specific areas.”
CI: Cetations and cephalopods raise an issue: they are two of the other potentially highly-intelligent denizens of Earth four billion years after life started, but they’re not creatures that will ever do SETI. Is SETI an act of faith?
CC: I think that’s a silly way of looking at the problem. In what sense is the search for a room-temperature superconductor an act of faith? Science is exploration, and we don’t know whether intelligence is common or extraordinarily rare or even absent in the universe. We have a very small number of ways of addressing that problem scientifically. Addressing virtually any question systematically and in a reproducible way isn’t an act of faith—it’s an act of exploration.
CI: Given the difficulty of constructing the experiment, how can we do this in the least anthropocentric way possible?
CC: All the ways of searching for life make different assumptions. The search for extraterrestrial intelligence doesn’t make an assumption about life being carbon- or water-based, but it makes some of the most powerful assumptions, in that it requires the existence of extraterrestrial technology. The field of radio telescope SETI has improved substantially in that respect in the last forty years, simply by overcoming technological limitations. SETI was once in a realm where it had to choose so-called magic frequencies; that was an almost hopeless situation that clearly required a disturbing amount of anthropomorphic thinking to make a choice. Now that we’re in a realm where we can scan across ten or so gigahertz of frequency and allow the frequency to drift, we’re in a much better space with respect to a potential signal.
There is a principled argument that there’s a region in the electromagnetic spectrum—still a region we can only sample a fraction of, but not an infinitesimal fraction—where the signal-to-noise and sensitivity are best from the point of view of interstellar communication. It’s not the only potential argument, and Charles Townes has for years argued to look for extremely narrow-band optical signals; we’re doing some pilot projects in that area now. It would be foolish to suggest that anthropomorphic thinking doesn’t haunt this work.
CI: We move at the leading edge of our own technology. An advanced civilization might be able to manipulate gravity so as to make gravity waves, but we’re barely learning how to detect them ourselves.
CC: Or neutrino beams, or tachyons (if they exist), take your pick. But it’s not quite that grim. I agree that’s an issue, that these may be exactly the wrong places to look and maybe everybody’s talking to each other with gravity waves or neutrinos. But the advance of technology doesn’t just move you from the latest anthropomorphic system to the next; it also enables a slow reduction in the level of anthropomorphic thinking. You still have the dilemma that maybe everyone’s talking to each other with exotic particles, but we’re doing better now than we were before. It’s a tough problem—and it’s exploration, not a well-defined laboratory experiment—but that’s true for a lot of exciting science.
CI: One last question. Accepting SETI as a provocative and well-placed side bet, what in the next decade do you think the real excitement is going to be in astrobiology? Where can we make a breakthrough?
CC: The Kepler mission, assuming that we actually launch the damn thing and it works. I believe that will be a milestone in human intellectual history. It never gets as much press as the Terrestrial Planet Finder, which keeps receding into the distant future, but I think knowing the frequency of Earths and their orbital properties will be a huge step forward. It could turn out that Earths are fairly common and that some of them are in the habitable zone. That doesn’t prove that life’s out there, but it has a huge impact psychologically.
CI: Astrobiology gets mature when it gets statistical, but statistics are boring to most people. They won’t pay attention to the three hundredth extrasolar planet, but that’s actually when the field matures.
CC: It may be that you’re right, that discovering the fortieth Earth will be much less exciting than discovering the first, second, third, or tenth Earth. But knowing that there are a hundred Earth-like worlds out there will seep into the popular consciousness. It will go from, “Well, there have got to be a lot of Earths out there,” to, “Wow, there really are!” That will have a huge impact.