James Kasting

Editor’s note: Prof. Kasting reviewed and corrected this transcript in 2024. Major insertions are marked with his initials, JK.

Varga:

This is Ian Varga. I am interviewing Dr. James Kasting at Pennsylvania State University in State College, Pennsylvania on July 25th, 2018. So, first, we’re going to go all the way back to the very beginning. So, where did you grow up originally?

Kasting:

Well, I grew up in various places. I was born in Schenectady, New York; moved almost immediately to Cincinnati, Ohio and lived there for eight years; moved back to Schenectady for two years; moved down to Huntsville, Alabama for about seven years, and then to Louisville, Kentucky. 

Varga:

Why did you move around so much?

Kasting:

My father worked for General Electric, which is sort of like working for the military. 

Varga:

Who did you grow up with then, in your household?

Kasting:

Well, my father and mother, and my twin brother, Jerry, and my younger sister Sandra. 

Varga:

You mentioned that your father worked at General Electric. What was his profession there?

Kasting:

He was a mechanical engineer, who sometimes worked as an electrical engineer. 

Varga:

So, he had a full education, then—a college education?

Kasting:

He had a bachelor’s in engineering. 

Varga:

What did your mother do as a profession?

Kasting:

My mother raised us, and then she we went back to school, and then she taught calculus at University of Louisville for many years, as an instructor. 

Varga:

So, she was college educated as well?

Kasting:

Yes. She went to Wellesley, where she was a chemistry major .

Varga:

Okay. So, then did your parents have any particular influence, then, on your choice to become a scientist, or to pursue an education?

Kasting:

They had influence, but I also read a lot of science fiction, and that got me interested in science, and I spent part of my youth growing up in Huntsville, Alabama, which was home to NASA’s Marshall Space Flight Center, so we had space all around us. 

Varga:

So, in general, what was it like to live in these places while you were growing up? Do you have any particular memories?

Kasting:

Huntsville was quite inspiring, actually. This was during the Apollo program, and they were designing and testing first the Saturn IB, and then the Saturn V. They would bolt them down out at Marshall, and fire engines for like three minutes at a time, and the whole city would shake. So, you could not ignore the fact that the space program was on. 

Varga:

So, then, in Huntsville, you had access to a lot of different resources, I imagine, in terms of education, and in terms of your interest in science?

Kasting:

I went to the public schools there, which were okay. They’re probably not as good as the public schools up north, but it was a reasonable education. Half the people in Huntsville were imported from the north because they came down as part of the space program. So, it was actually a very educated community. 

Varga:

So, you had an explicit interest in science growing up then?

Kasting:

Yeah, I was basically always interested in science.

Varga:

Did you do any extra-curricular activities while you were in high school, or anything like that?

Kasting:

Nope, just read science fiction. Well, I did sports activities. 

Varga:

Like what? 

Kasting:

Wrestling, and tennis. I guess those were my two big sports. 

Varga:

Were there any teachers or any other major figures that you see as being an inspiration for your career?

Kasting:

I had a couple of English teachers who were really good in high school. I think they were my best teachers. 

Varga:

Why do you think they were so influential?

Kasting:

Because they taught me how to write. At least, they started the process. 

Varga:

So, do you think writing is a really important part of what you do as a scientist?

Kasting:

I spend most of my time writing. 

Varga:

Do you think that’s somewhat of an unspoken top part of science—the writing portion of it—or is it something that scientists are aware of?

Kasting:

Some scientists are aware of it. I would say the biggest weakness of many of the students that I’ve worked with is they need to learn how to write better. I did, too, when I was a student. But that’s how we communicate our results to each other, and to the public. 

Varga:

Since we’re approaching the 50th anniversary of Apollo 11, do you remember the launch, and what was your experience?

Kasting:

I don’t remember the launch of Apollo 11, no.

Varga:

Or anything about the landing?

Kasting:

I know there were 6 moon landings. Was that the first one?

Varga:

The first one was Apollo 11, yes. It was in 1969.

Kasting:

Sure, that was Armstrong. So, yeah, I remember that, but more from the news reports, rather than remembering it directly. 

Varga:

So, when you began your college education, what sort of career were you expecting to pursue?

Kasting:

I knew I wanted to be some kind of a scientist. I was interested in astronomy, but I didn’t think that was that practical, or my parents didn’t think it was that practical. So, I started out as a chemistry major, and then switched to chemistry and physics after a year, because I found out I could through with doing fewer labs that way. I think I was always a theoretician. 

Varga:

So, you prefer the big ideas in science as opposed to the collection of data or experimentation?

Kasting:

Yeah, I’ve tried to sort of stick to “big idea” stuff. You can do that as a theoretician. It’s hard to do that as an experimentalist. 

Varga:

Is there anything in particular that turns you off from being an experimentalist?

Kasting:

I just don’t think I’d be very good at it. I’m not that good at mechanical things. I admire good experimentalists, and good observers or data gatherers, but I think my thing is more like picking up problems I can solve on the computer, and then designing computer codes to solve them. 

Varga:

So, why did you choose to go to Harvard for your undergraduate education?

Kasting:

Oh, you know, I applied to one Ivy League school. I applied to four schools total, and got into Harvard, and I got a nice scholarship from them, so that ended up being the cheapest place I could go. It made the decision pretty easy. 

Varga:

Did you have any prior connection to the school at all, whatsoever? Maybe your family?

Kasting:

No, but, you know, they have the geographical distribution requirement that they try to fill, so the competition getting in there from Alabama was not as tough as I’m sure getting in from the East Coast. Plus, I think they liked my essay. I wrote it on the space program and growing up in Huntsville. So, I probably stood out from a lot of the other applicants. 

Varga:

So, why, ultimately, did you choose to major in physics and chemistry?

Kasting:

Well, I started out with chemistry, because it’s good background, but then I decided I like the physics part of chemistry better than the chemistry part. Physics, I think, is the most difficult subject. Although, pure math, I’ve never really tried. That would be difficult for me, I’m sure. But I always felt like I learned things in physics classes, and I was curious about quantum mechanics. I just liked learning things from first principles, which is what you do in physics. 

Varga:

What do you mean by “first principles?”

Kasting:

Applying Newton’s laws, or whatever. Applying math to physical problems and getting answers that are verifiable. 

Varga:

Why do you think physics is the most difficult?

Kasting:

Because you’re applying math to physical problems, and you have to learn the physics of it, and the math, usually at the same time, because oftentimes in the physics classes, we were ahead of where I was in math classes. It’s particularly true when you get up to electricity and magnetism. There’s a lot of math there that most of us learn for the first time in physics classes. 

Varga:

More so than in chemistry? I know chemistry is a relatively mathematical field as well. 

Kasting:

There are branches of chemistry that are pretty mathematical, but basically every branch of physics is mathematical. 

Varga:

So, what was it like to study at Harvard in the early 1970s? 

Kasting:

It was a little overwhelming for me because there are so many bright people up there, and you’re just trying to figure out if you fit in and can really compete with all those folks. Not just the professors, but your roommates. The competition was pretty fierce. There were three different batches of students there. There were the scholars, like myself, and then there were the student athletes, and then there were the people that got in there because their families had gone to Harvard for a long time, and they’d given them a lot of money. So, actually that kind of brought the barriers down a little bit, and made it more tolerable than it would have been otherwise. 

Varga:

So, what was the student atmosphere like, this being a rather contentious period on college campuses across the country.

Kasting:

Well, it was only contentious for one year, while I was there. My first year was ‘71-’72, and that was the last year where there were protests against Vietnam, and there were marches at Harvard Square. And then we basically pulled out of the war. The draft ended, and it was quiet after that. 

Varga:

Were there any particular professors, or colleagues at Harvard, that you’ve worked with, that had a lasting impact on your career?

Kasting:

Well, let’s see. My advisor was a Nobel Prize winning chemist, Dudley Herschbach. But I’d meet with him once a semester, and I don’t think he had a long-lasting effect on my career. I had a Nobel Prize winning physicist for first year physics, who was Edward Purcell, who basically discovered NMR. He was inspiring, but I don’t think he… I was never going to be a Purcell. I had an astronomy professor my senior year—a young guy named Peter Foukal, who was just a lot of fun. I finally took an astronomy course my senior year. So, I’ve always had a foot in astronomy ever since then. 

Varga:

Was it somewhat daunting, then, to work with, or to be in classes with these somewhat famous scientists? Were you intimidated at all?

Kasting:

Well, you know, we worked pretty hard. My first semester I worked six nights a week, and then after that I decided that was too much for me, so I took Friday nights and Saturday nights off. I was working the rest of the time, so working pretty hard. Not nearly as hard as the guys from MIT, who were just up the road. I used to chat with them because I was a JV wrestler, and we would wrestle those guys. They thought we all had it pretty cushy, actually. 

Varga:

So, then, how did you get so involved in astronomy? You said you took astronomy classes in your senior year. Was there any other inspiration for that?

Kasting:

Well, I just wanted to take some astronomy, so I did, and then in graduate school… I had friends from back in Huntsville who gave me advice on graduate school, so I wanted to go into space science, and they basically sent me out to work with a guy named Peter Banks at UC San Diego. Banks was a magnetospheric physicist. I spent a year learning about the upper atmosphere, and whatnot. The first thing Peter told me when I walked into his office was that they were shutting down his department at the end of that year, and that he was moving to Utah State University. So, he assigned me to work in the lab with a guy from Michigan, Paul Hays, who was out there on sabbatical, and I ended up following Paul back to Michigan to finish up my PhD. 

Varga:

So, that’s why you chose to go to University of Michigan for grad school? 

Kasting:

Yeah, so I got to Michigan by accident. Then actually, I switched advisors when I got there, because Paul was an experimentalist. He was also building instruments to study the aurora, and the charged particles in the upper atmosphere. He wanted somebody to go on a boat that was going to go up to the Arctic and get frozen into the sea ice for three months, during the winter, and take spectra of the aurora borealis, and I figured that was not me. Plus, I had done a term paper on the rise of oxygen when I was out in San Diego, and that actually got me interested in the problem, so I read a lot of geology papers—the geologists are the ones who care about it, but also atmospheric physicists—and so I got interested in this question of “How much oxygen can you build up before there’s photosynthesis?” So, that’s what I worked on for my PhD thesis, which was strictly theoretical. 

Varga:

Who was your other advisor, then?

Kasting:

So, my new advisor was Tom Donahue, who was also very well known. Michigan had a very strong department. It was then called Atmospheric and Oceanic Sciences, and then they added space to that. Tom Donahue was a well-known upper atmospheric chemist and physicist. I didn’t actually work with Tom. I worked with a guy who was junior faculty, who was on Tom’s payroll, Shaw Liu. Shaw had developed a photochemical model for looking at ozone depletion, and also hydrogen escape. So, what I did for my thesis is I borrowed Shaw’s photochemical model for the modern Earth, and I modified it to do the oxygen problem. Tom Donahue was gracious enough… he had all this money—he was a PI on Voyager and had all this grant money. He was gracious enough to support me to do my own thing, even though I wasn’t really doing what he had grant money for. Then, Paul Hays, my first advisor there, introduced me to Jim Walker, who at the time was at Arecibo Observatory, the radio telescope down in Puerto Rico. Jim Walker was in the process of writing a book on the evolution of the atmosphere, so I got an advance copy of his book, and I basically formed a lot of ideas from reading that… he did calculations pen and paper, and then I built computer models to do that in more complicated fashion. So, Jim Walker was really my main academic mentor at that time. I had a bunch of good academic mentors who helped me along in many different ways. 

Varga:

Was this all rather difficult, or time consuming, or a stressful process… graduate school?

Kasting:

No, for me it was like summer vacation the whole time. The competition was not nearly as hard as it was at Harvard. Plus, once I got through my course work, I was working on my thesis. I loved it, actually. It was a lot of fun. I was just writing my own code. I basically did my own thing. So, that’s what got me back into astronomy, actually. It was a very circuitous route because at my PhD defense… to figure out how much oxygen there was in the atmosphere, I needed to know how much CO₂ there was, because you can make oxygen photochemically from CO₂. So, I read up on CO₂, and I learned about the faint young sun problem on the Earth. The sun was 30% less bright, but the Earth wasn’t frozen over. And then I read up on geochemistry and learned that CO₂ ought to build up because of the carbonate silicate cycle. I wasn’t that interested in it, but Jim Walker asked me a question in my thesis defense. He said, “Well, you said in the thesis that CO₂ would build up if the Earth ever froze over, but do you think it would just oscillate like that, or would it find some steady state?” I said, “I’m sure it would find some steady state, but I don’t know how to calculate that.” A year later, after I graduated, I got a manuscript in the mail. Jim Walker had worked out the whole problem, and put me on as third author. The paper was entitled A Negative Feedback Mechanism for the Long-Term Stabilization of Earth’s Climate. That was a really good idea, which was partly mine, and partly Walker’s. That’s still my second or third most highly cited paper, after all these years. That was then the basis for much of what came next. After that, I did a post-doc at NCAR, the National Center for Atmospheric Research, where I learned some things about numerical methods. Then I got a chance to go out and work with Jim Pollack out at NASA Ames. Pollack was Carl Sagan’s first graduate student, and he wasn’t so interested in the oxygen problem, but he was interested in the climate problem, because he was… one of many things that Jim worked on was planetary climates. So, I got out there, and I stayed there for seven years, and during that time I developed my photochemical model and climate model, and then I got interested in the habitable zone question. [JK. The habitable zone is the region around a star where a rocky, Earth-like planet can support liquid water on its surface.]

When I was a graduate student at Michigan, Michael Hart had published two papers: one on the habitable zone around the sun, and another around the habitable zone around other stars, and he concluded that habitable zones were really narrow. He actually had a very crude carbonate silicate cycle in there, but he had a bad model of the greenhouse effect. In fact, he had some axes to grind, as I’ve learned later on. He was a creationist, and white supremacist. So, those are things I usually don’t mention in talks, but it turns out that if you do the greenhouse effect right… if you include the carbonate-silicate cycle, and do the greenhouse effect right, then the outer edge of the habitable zone is much farther out than Hart had calculated. So, we got a rather wide habitable zone compared to Hart’s skinny one. The astronomers care about that. So, that was all theoretical, but that paper was published in 1993. Then, in 1996, the first exoplanet around a main-sequence star was discovered, 51 Peg b, and now we know that there are planets within the habitable zone of nearby stars, and we’re hoping to build big space telescopes to investigate them. So, that went from being fringe science to actually something that a lot of astronomers care about. 

Varga:

So, during your education, were there any major controversies in your department, or science, that you remember? Or, what was the atmosphere like among the scientists?

Kasting:

From my perspective, it was all hunky-dory. I never ran into any controversies. I know two of my advisors, Jim Walker and Paul Hays, got into a big spat years after I left, so I mean, there were things that went on, but I somehow escaped all of that, and went through without any controversies. 

Varga:

Okay. So, you mentioned in your dissertation, which I have the title here. It was Evolution of Oxygen and Ozone in the Earth’s Atmosphere. Why did you pursue this as your dissertation topic? 

Kasting:

Because I read up on the rise of oxygen paper, and I read this series of papers by Lloyd Berkner and [Lauriston] Marshall. They wrote a series of very influential papers back in the ’60s on this abiotic oxygen problem, and it turned out, they did it entirely wrong. Jim Walker figured that out, and I sort of figured it out, but I had Walker’s book to guide me, and it took a long time before it all really clicked. But I got interested in that problem, and then I was lucky enough to have an advisor who would support me and to get this photochemical code from Shaw Liu that allowed me to do that problem. Shaw didn’t think that I knew what I was doing, though, so we used to argue about how to solve this problem. Fortunately, that didn’t prevent me from going ahead with it. 

Varga:

Why would they think that it was not plausible?

Kasting:

Because it’s a case of the tail wagging the dog. The photochemistry of oxygen and hydrogen in the atmosphere is actually very fast compared to the processes that control the amount of hydrogen, which are volcanic outgassing at the surface, and escape to space at the top. What Walker had figured out correctly, doing it back in the envelope, is that, to first order, you just balance the volcanic outgassing rate of hydrogen and other reduced gases with the rate of hydrogen escape to space. If you do that, and then do some rather rudimentary chemistry, you can figure out that there’s not much oxygen in the atmosphere. That’s true. I then did it with a one-dimensional photochemical model, so it was vertically resolved, and it’s a little more complicated because then you get a big oxygen peak up in the stratosphere from photolysis, but near the surface, oxygen’s way down, just like Walker had said. It’s these relatively small fluxes… it’s the inputs and outputs that control the redox state of the atmosphere. The photochemistry is going much faster, but it’s controlled by the… you know, the photochemistry is the dog, and the input and output of reductants is the tail, which wags it. The tail wags the dog. 

Varga:

So, how did you obtain your position at NASA Ames?

Kasting:

Oh, I was out there on a post-doc, and it’s hard to get a civil servant position out there. They wanted me to stay on as a research scientist, but I wanted to get a stable position, so I got… there was a post-doc offered at NASA GISS [Goddard Institute for Space Studies], so I went and interviewed for it, and got an offer for that. So, I got an offer there and went back and then they… I had done a paper with Jim Pollack, a fairly complicated paper on hydrodynamic escape. Anyway, they liked the paper, and they all of a sudden… there hadn’t been a civil servant job, but all of a sudden, one opened up, and I got the slot. Actually, I got the second slot. The first one went to Steve Squyres, who went on later to become famous as the PI for the MER rovers on Mars. He wasn’t famous back then, but he was clearly an up-and-comer. I realized there was competition out there. Of course, Ames couldn’t hold onto Steve either. He left for Cornell. 

Varga:

So, what is it like working for NASA Ames, and what is like compared to an academic position?

Kasting:

It was wonderful, actually. I did eventually get tired of it. I wanted to get back and have more contact with students. I think I felt like I was spending too much of my time staring at my computer screen. I was out there for seven years, and that basically gave me a long time to develop a climate model, and work on the photochemical model, so most of the tools that I’ve used in my research ever since then, I developed at or before… I mean, I already had a photochemical model going, but I built a climate model essentially from scratch by stealing stuff from my colleagues and compiling them together. That allowed me to do the habitable zone calculations. If I had gone straight into academia, it would have been more difficult because you’re trying to teach and you’re trying to bring up students. I don’t have nearly as much time to do my own thing now. So, I would recommend it for any theoretician to work at a national lab like that for a while. 

Varga:

Why did you leave then?

Kasting:

Partly because I wanted to have some students. Partly… actually, maybe even more so because my wife’s family was on the East Coast, and my family was in the Midwest, and we’d been out west for 9 or 10 years by that time, between Colorado and California, and we had small kids. So, I wanted to get moved east of the Mississippi. So, it was a combination of those things. Plus, the fact that I could see that Ames… it was not obvious to me what purpose Ames served in the NASA hierarchy. We were in the space science branch, but the very year I got there as a post-doc, NASA made a decision that all of their planetary missions were going to be done out of JPL, so Ames lost that part of its charter. I remember I used to wonder, why did they bother supporting a theoretical studies branch? Normally NASA has scientists who support various missions. After we lost the missions, we didn’t really have that at Ames. They’ve survived pretty nicely since then, but they went through some down phases where they thought they were going to get abolished, and I thought I could see that maybe coming. 

Varga:

So, life on the West Coast didn’t suit you as much?

Kasting:

It was beautiful, of course, but with small kids, both my wife and I were working, you have to have… unless you’ve got one really good high-tech job, you have to have two normal salaries just to make things meet, and it was a real rat race, basically. So, it was very pleasant when we moved to State College here, and my wife stayed home for a few years when the kids were home, and then she eventually went back to work part time. So, it was good from a family standpoint. 

Varga:

So, why, ultimately, did you end up at Penn State?

Kasting:

It’s the third place I interviewed. The first place I interviewed was University of Chicago. I think I was pretty green, and I was talking about the greenhouse effect, and the faint young sun problem, and [JK. then I got myself into trouble.] There was a famous scientist named Sherwood Rowland, who had shared the Nobel Prize in Chemistry for his work on ozone. Rowland had also worked on the greenhouse effect, [JK. and he had written something about the possibility of a runaway greenhouse on Earth that I disagreed with.] I said something about him that was not very complimentary. It turned out he was a University of Chicago grad, so I think that fairly well did me in. 

Varga:

So, what, ultimately, are your responsibilities here at Penn State?

Kasting:

Well, I came in as an associate professor, but as a professor, you’re supposed to bring in money for the research, and teach classes, and bring along graduate students, and get some graduate students through the curriculum. So, that’s what I do, and that’s what everybody in the department does. 

Varga:

How much teaching do you do?

Kasting:

When I first got here it was one course a semester, so two a year. For the last ten or fifteen years, it’s been three a year. Which, you know, that’s fair enough. I think that’s what Penn State can afford. It’s more than you teach at Ivy League institutions, and in fact, there are parts of Penn State where they teach less than that, but that’s what we can afford here in Geosciences. I consider it a good deal. It allows me enough time to still pursue a lot of things that I’m interested in. 

Varga:

Are there any other administrative or institutional based duties that you have here at Penn State?

Kasting:

I am the Chair of the astrobiology dual title program, which is not a major responsibility. I am Chair of the Earth Systems undergraduate minor, which is also not a big responsibility. So, I’ve actually managed to stay out of administrative posts, pretty much. 

Varga:

How has your experience at Penn State changed over the course of your career? Has it changed since you got here initially?

Kasting:

I have more students. For a long time, I only had one student, which was actually good, because I was still working on my habitable zone stuff. I actually was still doing a lot of my own work for the first several years. I think it delayed me getting up to full professor, because I didn’t have enough students in the pipeline. I had nobody applying for many years, and then eventually people discovered me, and I had students applying. That’s good and bad. It’s good you can actually get more work done if you have good students, but then you have less time to think. It’s been on the whole really good because I now have three… two ex-students, and an ex-post-doc, who are heavily involved in these big space telescope missions. That way, I don’t have to be directly involved myself… I’m getting too old, and I’ll be lucky to even see HabEx and LUVOIR [Large UV/Optical/IR Surveyor] go, but my students are involved, and I’ve taught them what I know, so it’s actually very comforting to me to know. [JK. Since this interview was recorded, HabEx and LUVOIR have coalesced into the Habitable Worlds Observatory, HWO.] There are things like that oxygen problem that I thought was just interesting theoretically. That’s become a big issue. In fact, we just had a seminar from my former student, Sonny Harman, on false positives for life. So, we think we’ve developed a good methodology for dealing with that. It goes back to my thesis, but we’ve refined it over the years. Just like Berkner and Marshall got the wrong answer, lots of people get the wrong answer on that problem, and it matters. Now, if we see oxygen or ozone in an extrasolar planet, we want to know whether that’s a biosignature or not. So, you need to know how to do that calculation. 

Varga:

So, you’ve been on a number of different committees and panels over the years, with NASA and other places. How generally are these panels organized for scientists, and how do you become involved in them, so the historians can know better how this process works. 

Kasting:

The ones that have mattered the most, to me, were the space telescope ones. I got on the TPF Science working group way back around 1996, or late ‘90s. TPF was Terrestrial Planet Finder. I’d been working on the habitable zones problems, but I had no idea that you could actually look for habitable planets and get observations. Then I heard a talk by Roger Angel from University of Arizona about how to do this mission. At the time, we were thinking of doing it in the thermal-infrared, but then a lightbulb went off, and… I forget. I knew some people at NASA and somehow I got onto the TPF Science working group. Then, that morphed into, briefly, back in the early to mid-2000s, the JPL people got in control of the situation they thought they did, and we started doing a pre-phase A design study for TPF-C, the coronagraph, and I got selected to be the co-chair of that endeavor. That was the most fun thing, scientifically, I’ve ever done in my career, even though it only lasted six months before they cut the money off. It was really big-time. 

Varga:

Why was it so enjoyable?

Kasting:

Because it was exactly what I wanted to do and would have been a multi-billion-dollar project. These days, it’s like what HabEx is—the Habitable Planets Explorer. There are these two flagship concept missions that NASA is studying right now, HabEx and LUVOIR, and both of those would do what TPF-C would have done, only better, because the technology has come along, and LUVOIR would be quite a bit bigger. But that, to me, would be the ultimate scientific discovery, to find Earth like planets around other stars in their habitable zones, and get spectra of their atmospheres and look for life. I mean, what could be more fun?

Varga:

That’s true. Yeah. So, much of your work is related to early Earth’s atmosphere. So, what do you think are your main contributions to this field, and how is the field evolved or changed since you began?

Kasting:

So, my main contribution… actually two things. One is the faint young sun problem, which, that started out just as that paper that came out of my thesis, which I didn’t do any of the work on. Jim Walker did. But while I was at NASA Ames, I built my own one dimensional climate model, and then was able to look at that problem quantitatively, with the climate model. So, that’s one thing I’m known for. Then, the other is the oxygen problem. We think that oxygen was low prior to 2.5 billion years ago, back in the Archean, and these models that we do can describe that. I think my fourth most highly cited paper is one on sulfur mass-independent fractionation, which if you keep track of sulfur isotopes in an atmospheric model like that, you can place quantitative limits on oxygen back then. I should say that we didn’t break the ground on this problem. The real breakthrough was a paper by James Farquhar and colleagues back in 2000. But after that my then-graduate student Alex Pavlov took the photochemical model, and put the sulfur chemistry in there, and that paper has been cited a lot, because that’s actually our firmest constraint now on atmospheric oxygen back then. 

Varga:

What are the big questions left to resolve in this field?

Kasting:

Oh, well, for the Achaean, we’re still working on the sulfur MIF, as we call it, Mass Independent Fractionation. We think everybody, including us, has been misunderstanding the fractionation mechanism. This is something that was pointed out two years ago, now, by a quantum chemist at Marquette, named Dmitri Babikov, whom I met at a meeting about two years ago. So, we’ve been pursuing that. There’s all sorts of questions related to the evolution of oxygen. One of the big ones that we’re not really working on directly ourselves is after oxygen goes up, how high does it go up? Does it go up to present levels? Nobody thinks that, but now some people think it only went up to like .1% of the present. 10^-3 PAL [times the Present Atmospheric Level], and that’s based on some geochemical indicators. The evolutionary biologists care about this because they want to know animals were developing during the Proterozoic, and they want to know whether they were limited by oxygen, or whether they limited by other evolutionary factors. So, I would say that’s one of the biggies that’s out there right now. 

Varga:

So, some of your other publications are talking about the CO₂ levels as well in the early Earth’s atmosphere, and does this research have implications for present atmospheric conditions or environmental conditions?

Kasting:

Not many. The modern problem—actually, Jim Walker and I wrote a paper on this many years ago, and others have since done a better job, but the CO₂ that we’re putting into the atmosphere right now is not going to go away in any short time frame. You hear all this worry about CO₂ doubling, but you know, CO₂ could go up by a factor of 8 or 10, if we burn all the fossil fuels, and it will take tens to hundreds of thousands of years to get rid of it, so the potential problems are huge. Even in the short term, I think the problems are huge. They’re really daunting, and we have to solve that problem. 

Varga:

So, you’ve mentioned that you’ve worked with Jim Pollack, who was Carl Sagan’s student. What was it like working with him?

Kasting:

Well, it was wonderful. Jim was just a great collaborator. He was collaborating with five or six different people all the time, and somehow he could compartmentalize things and go from one problem to the next. He would stay home in the mornings, and do his own thing, and then he’d have a series of meetings every afternoon. He also brought a really talented group out there—there was a Cornell-to-Ames pipeline, actually, because Carl Sagan would get good students and then he’d send them out to Jim to do their postdocs out at Ames. Jeff Cuzzi came that route, and Brian Toon, and Steve Squyres, and probably some that I’m forgetting… it was just an excellent research group out at Ames. 

Varga:

So, how did you translate your work on the Earth’s atmosphere to Mars, when working with him as well as with others?

Kasting:

Because Mars… On Earth, you have a faint young sun problem that is easy to solve. On Mars, it is much harder to solve, because it turns out you can’t solve it just with CO₂ and water vapor. When I finally realized how to do the outer edge of the habitable zone, it was actually a guy named Ray Reynolds at Ames, who suggested the idea. I always thought the outer edge of the habitable zone was determined by Jupiter, and the asteroid belt and what not, but Ray just sort of casually remarked sometime, “Isn’t there some point at which the CO₂ starts condensing out?” I thought about that, and yeah, that has to happen. I had done a paper with Jim Pollack about warm early Mars, warming it up with CO₂, because I developed this climate model, and I did some calculations saying that you could warm up early Mars with about five bars of CO₂, but after chatting with Ray during one of these summers that I was back there visiting, I went back and looked at it and the CO₂ was super-saturated in the middle part of the atmosphere, and I’d realized I had done the problem wrong. So, I went back and did the problem right, and showed that you couldn’t warm Mars that way. Then I went back to the habitable zone problem, and that’s essentially how we determine the outer edge of the habitable zone these days. What’s the farthest out you can go with a CO₂ water atmosphere and maintain liquid water on the surface?

Varga:

So, how, then, did you become interested in extra solar planets, and get involved with that?

Kasting:

Well, as I said, through habitable zones, and getting on the TPF working group, and then I learned a lot about the extrasolar planets, and all these people were connected with the ground-based astronomers who were doing RV [radial velocity] measurements. We worked really hard on TPF-C there for a while, so I learned about the potential capabilities of these direct imaging missions. The bad news was that it all got cancelled, but the good news is it will come back, or we hope it will come back, and that they’re studying TPF-C-like flagship missions, which we hope one of those will get picked as the top priority for NASA. There’s two flagships lined up. There’s JWST, and then WFIRST [Wide Field Infrared Survey Telescope], but we’re hoping that one of the HabEx or LUVOIR will get picked as the flagship after that. Which, then, again, if we’re lucky, one of those could fly by the mid-2030s. [JK. A direct imaging telescope was picked as the next flagship mission by the astronomy and astrophysics 2020 decadal survey.]

Varga:

That’s a little ways away. So, how was your work on the Earth’s atmosphere then related to the extra solar planets?

Kasting:

It turns out to be different aspects of the same problem. The faint young sun problem is related to this question of how much warming can you get? How wide is the habitable zone? It’s the negative feedback in the carbonate-silicate cycle that determines both of those. Then, the early oxygen problem is related to this question of oxygen as a biosignature on extrasolar planets, so just by accident, all these things that I thought were interesting problems for the Earth, have morphed into being interesting problems for the exoplanet community. I was fortunate in that respect, in that I just sat in the same place, and then technology caught up, and all of a sudden, these calculations became… I wouldn’t call them practical, but they became more useful, and not just hypothetical issues. 

Varga:

So, were there any turning points, do you think, in extrasolar planet research, or any major discoveries that you think propelled the field forward?

Kasting:

Well, the Kepler Space Telescope has been a goal of mine, and that’s interesting, too. I had very early exposure to that, because the PI of Kepler is Bill Borucki, who was two doors down from me at NASA Ames… two doors down and across the hall. When I first got there, Bill was redoing the Miller-Urey Experiment in his little lab with a laser instead of with spark discharge. I liked Bill but considered him kind of harmless. I never thought he would come to much with the laser discharge experiments, but then he got this idea of doing the transit survey. The mission was not called Kepler, it was called FRESIP—the Frequency of Earth SIzed Planets. Borucki started working on that in 1984. I was actually a member of his team, because I was working on the habitable zones. Actually, it was probably in the ’90s, I guess, that he got FRESIP to that stage. But his idea eventually worked. It took Borucki 25 years to get the thing launched, but then it became the biggest thing in exoplanets. Most of the exoplanets that we know of were actually Kepler discoveries, even more than radial velocity targets. 

Varga:

So, do you recall the initial discovery by Geoff Marcy and Paul Butler, the Goldilocks planets in 1995? 

Kasting:

Yeah, so that was exciting. It was Didier Queloz and Michel Mayor who actually came out with that, and Marcy and Butler went back and found out that they had that planet and several others in their data set. They just hadn’t looked at the right periods. So, yeah, it was all a revelation, and it’s been very exciting ever since. I don’t stay on top of the exoplanet stuff so much anymore, because I’ve got my ex-postdoc, Ravi Kopparapu, [JK. now at NASA Goddard], who took over the habitable zone calculations. He really is an astronomer, so he’s the one who keeps tabs on all that stuff now. 

Varga:

Some scientists have characterized the mid-1990s as a turning point in the study of extraterrestrial life, broadly. Would you agree with this characterization?

Kasting:

I would agree, because we didn’t have any data until the 1990s. In fact, the first extra solar planets were actually the pulsar planets that [JK. my Penn State colleague] Alex Wolszczan discovered. That was 1991, I think, so it was several years before 51 Peg. 51 Peg was a bigger discovery, because that was a main sequence star. I think most astronomers already thought there were planets around most stars, but it’s one thing to think it, and another thing to have data. So, the ’90s were when the data started to arrive, and we’ve been getting data ever since, and now it’s the next big wave in astronomy. Cosmology had kind of dominated for decades, and X-ray astronomy was pretty big, but now exoplanets is, I think, becoming the biggest part of astronomy. 

Varga:

You think it is the biggest part of astronomy?

Kasting:

Well, in terms of the numbers... I haven’t been to an AAS [American Astronomical Society] meeting in a couple of years, but the last time I was there, 30% of the sessions were exoplanets. I see the youngest astronomy graduate students - more than half of them at Penn State are interested in exoplanets, so it’s a big deal. 

Varga:

Okay. So, what were your impressions on The Snowball Earth theory by Paul Hoffman in the 1990s, and what impact did this have on the field? Were there any precursors leading up to that?

Kasting:

Well, that really caught my attention, and we worked on that problem for quite a while. It’s fascinating, actually, that that could have happened. I never believed it until Hoffman wrote his paper. Joe Kirschvink had suggested the idea back in 1990. I was at the symposium where he suggested it, but it was really the work of Paul Hoffman and his colleagues, Dan Schrag, and I forget who else was on that science paper, but they really made a very convincing case that there were at least a couple of snowball Earth episodes in the late Proterozoic, and that got us interested from a climate standpoint. One of the big questions has always been how did photosynthetic life make it through the snowball Earth? So, I worked a little bit on that problem with Dave Pollard, pursuing what’s called the Thin Ice Model. There are different flavors of that now. There was either open water or thin ice over some substantial fraction of the Earth’s surface. I don’t think it was as hard a snowball as what Paul Hoffman imagines. 

Varga:

Do you think the model has any bearings on life on other planets and other moons?

Kasting:

Well, it does. One of the new developments in the habitable zone story was a paper that came out three years ago by Kristen Menou, up at University of Toronto, on limit cycling. He pointed out that for planets near the outer edge of the habitable zone… the carbonate-silicate feedback doesn’t always have to lead to a stable, warm climate. If you have either low volcanic outgassing rates, or low solar luminosity, then you can get limit cycling where the climate flips back and forth between totally frozen and deglaciate conditions. That’s still habitable, in some sense, but it wouldn’t be habitable by us, and not good for complex life. This is something that actually… Menou is the one that I finally… something clicked in my mind when he wrote a good paper on this. There is a Japanese scientist named [Eiichi] Tajika, who is a friend of mine, who had figured this out ten years earlier, but he was writing papers about the early Earth, and saying that if you had low volcanic gassing rates on the early Earth, you might get this limit cycling behavior. I even reviewed some of those papers. I just thought, so what? We think the volcanic outgassing rates were actually high on the early Earth. It wasn’t until Menou pointed out that this is a more general problem, that we paid attention to it. Then we worked on that, because it turned out Menou made some mistakes. He’s an astronomer, and he made a mistake by a factor of 10 in the Earth’s volcanic outgassing rate. So, things are not quite as dire as what Menou said, but the phenomena is a real one. 

Varga:

So, what were your thoughts on the Martian meteorite controversy that was going on in the 1990s?

Kasting:

Oh, I think it was overhyped. Al Gore is somewhat to blame for that, because he held a press conference at the White House. I’ve learned something about overhyping things. That happened with nuclear winter, too, during my NASA Ames days. There was a group called TTAPS—Turco, Toon, Ackerman, Pollack, and Sagan—who came out with the nuclear winter theory. Tom Ackerman was my officemate there, and Jim Pollack, of course, I worked with, so I knew all those guys. That’s when I first met Carl Sagan, because he used to come out to Ames during that time. Sagan made a big deal out of that, because he was very anti-nuclear. So, instead of just releasing that as an ordinary science paper, he put together a special meeting where he invited something like a hundred scientists to come in and vet the paper… all the things that you shouldn’t do with a controversial result like that. Then they published the paper in Science, and all hell broke loose, which I could tell because I was Tom Ackerman’s officemate. His phone rang off the hook for six months. Every right-wing, or a lot of defense guys who were pro-nuclear… it brought everybody out of the woodwork. I realized that what they should have done with that paper is just let it appear normally and quietly, and not hype it up, but that wasn’t Carl’s style. Same thing with the Martian meteorite story. That was hyped up with a White House press conference, and that should have been just a normal science paper, too. 

Varga:

So, what do you think is the broader significance of exoplanet research, and why is this something that other scientists, or the public, should be concerned about?

Kasting:

I think it’s a positive thing. There are so many negative things going on in our society politically. The environment and global warming is really scary to many of us, but it’s a political. But with exoplanets, there’s really nothing political about it. It’s just discovery, and it’s fun, actually, to work on a problem like that, where there is no political in-fighting. There’s in-fighting between JPL and Goddard over who’s going to get the next flagship mission, but that’s an entirely different type of politics, and it’s refreshing. I think there are philosophical implications for this, too. My colleague, Sara Seager, up at MIT, who’s really well-known in the field, is now Co-chair of the HabEx study team. She describes this as the second Copernican revolution, and I think, justly so. If we discover evidence for life out there, I think it will change our view of ourselves, just like Copernicus and Galileo changed our view of ourselves. So, I buy into that dialogue. 

Varga:

So, you were part of the astrobiology task force, and chairman of the exobiology peer review panel. What was the objective of the task force, and why were these formed?

Kasting:

The astrobiology task force… Jonathan Lunine was our chair on that, and he’s one of the sharpest guys I know. He’s also a natural leader on committees and things like that. He’s got a good personality for it. That was basically to write a short term strategy for exoplanets. It happened in the post-TPF days. NASA wanted a timeline for what types of activities to pursue, and I think we put together a good report. I was a minor player on that. Jonathan did a lot of the heavy lifting, and there were some really good people on that committee. Then, let’s see, I was involved the ExoPAG. I was the first chair of the ExoPAG, actually, and that was exciting for a while. I sort of ducked out of it because I wanted to pursue these flagship missions, and we went through a time when people didn’t want to talk about that. They wanted to talk about smaller missions, and I felt like I was actually getting in the way, because I was seen by some people as part of the JPL crowd that had gotten us into TPF in the first place, so I was afraid that I’d actually be counterproductive in that position. So, I stepped out of it. I think it’s been a good decision because it’s coming back on it’s own, and my students are all involved. 

Varga:

So, what role do you think NASA and its administrator at the time, Daniel Goldin, played in affecting extra solar planet research?

Kasting:

Well, he’s the one who got TPF started. He was the visionary. He also was responsible for starting the NASA Astrobiology Institute. We owe him a big debt of gratitude. On the other hand, he had his critics. He was the advocate for faster, better, cheaper, more reliable space missions. It’s basically impossible to do the first three of those and have it be more reliable at the same time. He was very unrealistic in estimating costs. I’ve heard lots of stories about the James Webb Space Telescope, which got started under Goldin. Part of the overcost on James Webb can be traced… well, some people trace it back to Goldin’s influence. But, you know, he was pushing TPF, and for a while there we thought we were going to ride that wave and do it, but then reality caught up. 

Varga:

So, has NASA consistently expressed interest in extrasolar planet research?

Kasting:

Oh, yeah. But there are different ideas on how to do it. Do you do it slow and build the foundation, or do you take a big leap forward, like TPF-C would have been? The astronomical community is actually very conservative, and they do everything… they’re very organized, politically, so they have these… every ten years they do a decadal survey. The biggest problem with TPF-C was it hadn’t been blessed by a decadal survey, so when the rest of the astronomical community got wind of it, they basically killed it. That’s why, this time we are trying to do it more carefully, and run it through the decadal survey, and get it blessed by the astronomical community. Then, I think it will eventually happen if that process works. 

Varga:

So, you consider yourself on the “big leap” side of the debate, instead of the small steps that you mentioned?

Kasting:

You know, I’m a “big leap” type. I’m interested in the big issues. We’re not going to learn much about Earth-like planets from [the] James Webb, I don’t think. We’re not going to learn anything about them from WFIRST unless they put a starshade on it. So, our first real chance to get data on Earth-sized planets that might be habitable, or inhabited, is going to happen with these big flagship direct imaging missions. I just hope that one or the other of them flies while I’m still alive. I’ll be long since retired, but that’s what we really need if you want to make a quantum leap forward, now, in our knowledge of exoplanets and the search for life. That’s what we need to do. You know, I was just on this committee, the astrobiology search for life committee from the NAS. We recommended that in our report, and there’s a parallel exoplanets report, and a big direct imaging mission is their number one priority. So, we’re all on the same page on that. 

Varga:

Is extrasolar planet research primarily an American endeavor, or is there international interest?

Kasting:

It’s very international. Mayor and Queloz were Swiss. The French were working on a direct-imaging mission, and the infrared called Darwin. I knew Alain Leger pretty well. He was the PI of Darwin. So, that one, just like TPF-C, got killed. It was a little bit ahead of its time, but it’ll come back. [JK. It has come back in the form of ESA’s LIFE mission, the Large Interferometer For Exoplanets.] Everybody I know in that business agrees that these missions ought to be international, because they have implications for all of mankind. They should be international. 

Varga:

So, how has astrobiology grown since 2000, and what issues does it have to overcome, still?

Kasting:

I think the Institute has been very good for it. Before that, there was the NASA Exobiology program, which you mentioned. I chaired that peer review panel for about six years. NASA was very much ahead of the game in funding that type of research since the 1960s. Then the Astrobiology Institute came about largely as a result of the 51 Peg discovery, and the Martian meteorite, even if that turned out to be bogus. That fueled interest and has really helped grow the community, because we’ve processed a lot of graduate students through that here at Penn State, so there’s now a healthy research community. Whether or not we can keep the Institute going is not clear. I’ve heard rumors that it may meet its demise. It’s big science, and a big pot of money. I’m going to try to carefully stay out of that discussion. [JK. The NASA Astrobiology Institute has gone out of operation, but it has been replaced with something called Research Coordination Networks that serve broadly the same function.]

Varga:

Okay. You’ve talked a lot about Kepler, and the impact it had on the field. What are your thoughts on the more recent TESS mission?

Kasting:

I’m curious about TESS. Do you know, is it still deploying properly? I haven’t heard boo out of TESS. I’m operating on the assumption that no news is good news, but I got an email from a colleague last week, or the week before, who was worried about it because he hadn’t heard about it. I’m crossing my fingers. We need for both tests to work, and more importantly, JWST. If that thing doesn’t work, then our chances of getting another big space telescope launched in my lifetime go down the drain. I pray for TESS. I’m not very religious, but I pray for TESS and JWST. [JK. Since this interview was recorded, both TESS and JWST have launched and have been performing spectacularly. Hurray!]

Varga:

I think I’ve heard that they delayed the launch, for whatever reason, but I haven’t heard about it since then. 

Kasting:

Well, no, TESS is launched, but I haven’t heard that it’s gotten successfully into its science orbit. JWST, of course, got delayed again. One of my graduate students, Becca Payne, has a graph out there… projected JWST launch date versus time, and it intersects the real-time axis at about 2028, or something like that. 

Varga:

So, what are your thoughts on the state of science, and space science in particular, presently in the United States. More broadly what do you think… in the current political climate?

Kasting:

Well, it’s generally been healthy. Space science is actually favored on both sides of the political aisle. Republicans don’t like orbiting satellites that give us information on the environment. Democrats don’t tend to like manned space as much, but they want to put that money into Earth orbiting satellites. I’m a fan of both. Some space scientists think that money spent on manned space is a waste, because it would be better spent on unmanned space. I don’t buy that. I grew up in Huntsville, so I think the unmanned space program tags along with the manned space program. The size of the pie is not constant. It grows, so I’m all for more of the above. The thing I worry about most is the economy. You know, we’re running up the budget deficits, and I’m worried we might not be able to afford these big, expensive things if we get ourselves over our head in debt. So, it’s another way where our scientific ambitions could be curtailed if we can’t afford them. 

Varga:

How do you convince the government or NASA to fund these sorts of large projects… these big science projects, or space telescopes, or whatever?

Kasting:

You need publicity. That’s why JWST has to work. If it does work, like the Hubble, you know, Hubble has generated all sorts of favorable publicity. Kepler generated publicity. JWST, if it operates the same way, will generate more interest, and then these things build on themselves. But if you get a big failure in there, you get a little activation energy barrier you have to get over again. We saw this with the Viking missions to Mars, which actually were successful, but they were unsuccessful in finding life, and Carl Sagan had probably overhyped those as well. You can’t just blame Carl, but NASA may have overhyped that. I remember after Viking, for about 15 years, you couldn’t even mention the idea of looking for life on another planet. Nobody wanted to hear about it. So, you don’t overhype things. 

Varga:

So, why did you write your book on how to find a habitable planet?

Kasting:

I started that right after TPF-C got canceled. I had learned a lot, so I thought I had something to write about. I thought it will be a long time before it comes back, so maybe I’ll write a book, and that’ll be my contribution to maybe helping it come back. 

Varga:

What is it like to write a science book? Did you try to gear towards the scientists or the public?

Kasting:

I tried to write a popular book, and I don’t think I entirely succeeded. I had too many things that I felt like I had to say in there, scientifically. One kind reviewer described it as a popular textbook. I know that it has been used for freshman seminars at Yale and at Princeton, so some people are using it, but it didn’t sell hundreds of thousands of copies. I think it’s a little too technical. I use it, actually, in my 400-level planetary atmospheres class. It’s a little too light for that, but it at least gets into the questions, and it’s got references in it, so I then supplement that with higher level material. We have another book that came out, which is much more technical. [JK. Atmospheric Evolution on Inhabited and Lifeless Worlds, Catling and Kasting, Cambridge Univ. Press, 2017.] Two thirds of that was written by my coauthor, David Catling. He’s written a tome, there, so that one is a good reference book, but I’m trying to decide whether I can actually use in my classes here at Penn State. I know I can’t use it in the 400-level class, or even for the 500-level astrobiology class, I’m not sure enough students will be able to read it. 

Varga:

So, was it designed to be a textbook?

Kasting:

David thinks it’s a textbook, but he’s got a different class of students out there. The 500-level class that I teach is called planetary habitability, and the last time I taught it, it was mostly astronomers. That’s changed, but we have a lot of exoplanet people up there. They can probably get through it. We get biologists in there. It’s an interdisciplinary program, and I guarantee you a biology student can’t read that book. 

Varga:

Are there interdisciplinary issues, then, in doing extrasolar planet research, because there are indeed a lot of disciples that cross over in this field.

Kasting:

Yeah. You almost have to know everything to solve the problem. Nobody, of course, does know everything. To me, it’s fun. It’s challenging, though. I’ve been going to origin of life meetings for a long time, before astrobiology was invented as a term. Those meetings are challenging too, for the same reason. It’s a combination of physics, and chemistry, and geology, and biology. I think the origin of life question is actually the most interesting and difficult scientific question. So, I think of astrobiology, and the search for life on exoplanets is one angle of getting at the origin of life question. We hopefully can answer the question of whether it happened more than once, which is something we don’t yet know. 

Varga:

So, are there any other accomplishments in your career that you’re most proud of, or that stand out to you, that you’d like to highlight?

Kasting:

Oh, I think we’ve been through most of the highlights, there. I mean, there are other things that I’ve worked on, but that’s a good enough list. 

Varga:

So, I have to ask this question out of curiosity. Do you think we’ll ever find intelligent life, or be able to communicate with it? Why or why not?

Kasting:

I hope we’ll find intelligent life, because there’s this concept called the Great Filter. Are you familiar with that?

Varga:

Explain it.

Kasting:

It’s one of the answers to Fermi’s paradox, of why haven’t we been contacted? From what I know, Fermi didn’t actually believe in Fermi’s paradox. Fermi didn’t believe in interstellar space travel, so he had a simple answer. He was talking about this with some colleagues at lunch, and one of them wrote it up, and the Great Filter says that there is some very difficult step between the origin of life and the development of the technical civilization, or space faring technical civilization. It’s difficult, and that doesn’t happen very often. It could be that life itself is uncommon. We’re going to answer that part of the question, I think, with these extrasolar planet studies, but if we find out that there is a lot of simple life out there, but we haven’t found any intelligent life that suggests that the Great Filter is ahead of us, rather than behind us. This goes back to the lifetime of a technical civilization, and the Drake Equation. We may do ourselves in—climate change could be what causes that. There’s different ways to do it, but climate change is the thing that worries me the most. I think this is going to happen on any planet, because whatever intelligent civilization there might be is going to go through a fossil fuel stage, like us, and they’re going to warm their planet’s climate. That’s dangerous, so that’s why I hope there are civilizations out there. It means that there are people who have figured out how to deal with these very pressing problems that we’re facing. 

Varga:

Have you considered giving any important documents or records to an archive?

Kasting:

I’m talking with my students right now about getting our programs up on GitHub. My papers are published, so those are available, but our programs—they’re a little scattered, and there are different versions, so we’d like to get them under version control, and that’s something tangible that I could pass down. So, I’m encouraging them to do that, and try to get organized about this. This is not just us. Lots of different research groups are getting codes publicly available in a controlled form. This GitHub, which I’ve only learned about in the last year or so, seems to be a good way to do that. 

Varga:

Do you have any other records that would be helpful for historians—any other papers, or anything like that?

Kasting:

No. You know, everything is published, just about. I try not to write things and then sit on them, so I don’t have a box of writings like people might have had in the old days. No, I think what you can find out there in the literature is basically everything that I’ve thought is worth saying. 

Varga:

Did you hear today about the news related to Mars, and the alleged discovery of a lake under the surface?

Kasting:

No, no. I’ll have to get on the web.

Varga:

Yes, that’s been sort of a big thing today.

Kasting:

Well, I’m really keen on Mars research, because we can go back there and find things out, and keep going back, and so it’s an ongoing source of excitement for me. 

Varga:

Do you think that there ever was life, at one point, on Mars?

Kasting:

I’m 50/50 on it. I try not to have preconceptions. I don’t see any reason why there couldn’t have been life on Mars, but you get back to the origin of life question. How often does it happen? We just don’t know. 

Varga:

So, you mentioned that you like manned space missions? So you’d be in favor of a manned mission to Mars?

Kasting:

Oh, yeah, because I think if there is extant life on Mars, it’s probably one or two kilometers below the surface. The models predict that you’ll run into liquid water down there, and I don’t think we’re going to be able to explore that depth without humans up there, and deep drilling equipment. It’s like the big space telescopes that we’re interested in. You need the big leap to really solve the big problem there. I think it’s easier to build these space telescopes than it is to get humans with deep drilling equipment on Mars. I don’t think I’m going to see that in my lifetime. 

Varga:

You don’t think it’ll happen in the next ten years, or anything like that?

Kasting:

No, not in the next ten years. We might get a man to Mars in twenty years, but it won’t be with the capability of drilling down and looking for life. We’ll be happy to get him to the surface and get him back in one piece.