American Scientist

Kevin Heng is professor of astronomy and planetary science at the University of Bern, Switzerland, where he also serves as the director of its Center for Space and Habitability. He is a core science team member representing Switzerland on the CHEOPS mission of the European Space Agency. He is the author of Exoplanetary Atmospheres: Theoretical Concepts and Foundations (2017, Princeton University Press). Starting in Fall 2022, he will be the inaugural Chair Professor of Theoretical Astrophysics of Extrasolar Planets at Ludwig Maximilian University in Munich, Germany. As a graduate student, Heng received a Sigma Xi GIAR grant that he used to travel to the Atacama Large Millimeter Array telescope in Chile. The experience, he says, confirmed his suspicions that he was better suited to be a theoretician. “I figured out on that trip that I just don’t think like what we call an observer, which was an eye-opener. The grant allowed me to understand that, and it had a big influence on my career.” Heng spoke about his career trajectory and objectives with American Scientist editor-in-chief Fenella Saunders. Read articles that Heng has authored about his research at www.americanscientist.org. This interview has been edited for length and clarity.

How do you categorize your research?

I consider myself a so-called methods theoretician. I’m interested in looking underneath the hood, not just using computer code or some equation that someone’s written down. I’m interested in, what are the assumptions? When does that break down? How is it all put together? There’s a whole body of work that my research group and I have contributed to, including things such as radiative transfer—how radiation interacts with matter—which you need for predicting what you see from an exoplanet atmosphere. Fluid dynamics, atmospheric chemistry, application of statistics, application of machine learning: They all have this underlying idea that you want to deeply understand the methodology you’re putting together.

My proudest piece of work is probably our 2021 Nature Astronomy paper. It solves a very old problem that was first written down in 1916; it’s 105 years old. The problem is, how do I understand the modulation of reflected light as a moon or planet goes around its star? If you look at the phases of a moon, you measure a reflected light phase curve that tells you about the scattering properties of the medium, be it a surface or an atmosphere. I’m proud of that paper because it gives you a closed-form solution you can write down on paper in a very general way. Our solution written down on paper is more accurate and much faster than the one solved on the computer, so you can use it to analyze data very quickly.

What has been your role in the mission of the European Space Agency’s CHEOPS (CHaracterising ExOPlanet Satellite), which launched in 2019?

I was with the mission at the very beginning in 2012; I still remember that when we received the phone call that the mission was approved, we were jumping for joy. I’m one of the five science team members for Switzerland in CHEOPS. I’m not an observer; I don’t calibrate and measure data. But what I do is, I try to be the bridge between the data and the interpretation, the theory. CHEOPS is a so-called photometric mission. We don’t have wavelength or spectral information. You look at light in one big broad range, a big bucket of wavelengths in the visible. But you can use that to look at the so-called secondary eclipse, meaning that when the planet goes behind the star, there’s a tiny dip in the light. Sara Seager at MIT showed that measuring secondary eclipses and reflected light gives you the albedo. We set up an albedo program, which is pretty successful. Then the other thing you can do is measure how the light is modulated as the planet goes in its orbit. This is called a phase curve, like the phases of the Moon. CHEOPS made me think about this albedo and phase curve business, which led to the paper in Nature Astronomy.

What is your approach as director of the Center for Space and Habitability at your university?

At the University of Bern, which is about 200 years old, we have never had a female full professor in physics. When I stepped into my first faculty meeting here, I actually gasped: I was the only non-Caucasian person in a room of 80 professors. As I progressed in my career, I stumbled into being the director of a research center. Suddenly I had to deal with all these issues. I had to worry about the male/female ratio when postdocs apply, I learned about the leaky pipeline, I learned about inclusivity issues. I had a diverse set of people in my center, so I had to worry about different aspects of culture. I found myself having to deal with this as part of the job, so I became interested in policy for that reason, plus my own personal experiences. I have to make decisions in an environment that is somewhat conservative, very male, and not very diverse. But I see it as an opportunity to make some changes happen.

How have you been trying to implement change?

I am not a particularly social person. I never thought of myself as an administrator. But when I became one, it was a fantastic experience, because basically it was a blank slate. I brought in certain ideas, and one of the advantages I think I have is that I’m originally from Singapore, I did my training at Colorado and Princeton, and I have a German wife, so I come from all three cultures in a way. So I came to this and my thought process was, why don’t I just take the best parts of my experience and try to put them together? One of the best experiences in my career was three years at the Institute for Advanced Study at Princeton. It’s a beautiful place, because it’s a crazy intellectual utopia. We’re just told to do one thing, which is follow your curiosity. If it’s beautiful—beauty not in the human sense, but in the abstract mathematical sense—and makes sense to you and you’re excited about it, just do it. Don’t worry about whether it’s practical. I was deeply influenced by that. And the philosophy there is that if you put really smart, creative people in the same place and you get out of the way as an administrator, then wonderful things will happen. You have to tolerate the fact that many of the conversations are just that—they’re just interesting conversations and nothing happens. But maybe 1 to 10 percent of the time, something wonderful is going to happen. You have to create such an environment to do that. With that naivete, I guess, I thought, how can I create some small version of that at this center? When I took over as director, the first thing I did was I got out of the way. I removed a lot of the bureaucracy. The second thing was, I started a fellowship program, and fellows can do whatever they want. After a while, we were very successful. We have about seven or eight fellows at any one time. I would say that’s the proudest thing I look at as a director. I managed to create this environment. I removed the bureaucracy. I installed these programs for people to interact and have discussions.

How do you think we can encourage more conversations across disciplines?

You have to create a space where people can speak without feeling like they’re going to be attacked or criticized. You have to get the right people in the room, rather than the right topics. What I mean by that is, you have to get people who are open-minded, not defensive about their corner of academia, willing to entertain strange thoughts in the way they think about things. I’ve found that it’s much more fruitful to work with the correct people in the right environment than trying to get the experts on certain topics in the right rooms.

How did your international background affect your view of academia?

I’m really an outlier. I went to basically bottom of the barrel schools in Singapore. I was a B and C student most of my earlier life; I nearly dropped out of high school. And in fact when I reached high school, I wanted to take advanced mathematics, and my grades were so bad they said, no, sorry, you don’t qualify. Which is ironic, because nowadays I’m known as an applied mathematician in the field. But I was just a mediocre student, all the way until I was 18. I landed in university and I got a D in my first undergrad course in physics and thought, wow, maybe this isn’t for me. But then I met two mentors, mathematicians who thought about things in very unconventional ways. They were just these two quirky personalities who finally allowed me to ask the question: Why should I bother? They had the answer to this question. For the first time in my life I realized, this is interesting. It’s not the “how” that’s interesting. It’s the “why” that’s interesting.

So you completed graduate school at the University of Colorado, then you did a fellowship at the Institute for Advanced Study?

The Institute for Advanced Study was a trial by fire, because I was searching for a topic that could really set off my imagination. One day I picked up Sara Seager’s book, Exoplanet Atmospheres, and I thought, oh, this is interesting. I have the background to do this. I picked the problem of these general circulation models, because I was told that it was one of the hardest problems you could do at the time, and I wrote a couple of papers on it. Not long after I was invited to give a talk at the Center for Astrophysics at Harvard. I wrote an email to Sara Seager and said, “Professor Seager, I’m here in Cambridge. You’ve never met me, you have no reason to know me, but I’m here and I’d like to talk to you.” Her reply, I think, changed my career. She said, “Hi Kevin. I know your paper. I really liked it, so please come talk to me.” I went to her, in this big office at MIT, and we talked. We exchanged ideas. At the end of this, she said, you know what, I’ve decided to be your mentor. Ever since that day, she’s gone to bat for me. What amazed me was that even though I had a record of like one paper on the topic at the time, she saw something in the way I did things that I didn’t see myself. I find her very inspiring, not just because of her papers, but because of her ability to see the big picture not just with the science, but with the people. If you look at the people she’s mentored, these are the movers and shakers in the field of exoplanet atmospheres.

How has your work in astrophysical modeling led you to consider simulations in other areas of science?

I’m generally interested in how we use mathematics as a language to describe reality. When you construct models for a long time, you realize that there’s no such thing as a universal model. A model is always constructed to answer a specific question, and therefore by implication you need to understand when your model breaks, when it becomes nonsensical. That’s my interest. Epidemiology is an example. These models use a so-called R number, the average number of people that an afflicted person will infect. But hidden in the R number are complex behaviors such as the biochemistry of the virus, the interaction of the virus with the environment, the interaction of people with one another. The R number also depends on the environment. It’s not something that is intrinsic to the virus. So I think that’s what a good modeler does. A good modeler doesn’t think that the model is a black-box sacred thing that tells you any answer you want. You need to understand the limitations, the caveats, and when the model breaks.

What is a future direction for your research?

Astronomy has a history of ingesting other fields. Roughly 100 years ago it ingested physics and then you had astrophysics. And then a few decades ago we ingested chemistry. It became astrochemistry, the study of organic matter in space. Now I jokingly tell people we have this half-nonexistent field called astrobiology, because we don’t have a way of understanding how life evolves as we have only one sample in the universe. There’s one very important marriage of fields that we have yet to achieve, and that’s between astronomy and geochemistry. We just wrote a big grant to the European Research Council called “Geoastronomy,” because we want to make that marriage. You need to understand the chemistry of a rocky body to actually predict what the rocks are. You care about that because if you want to search for life in the universe, you have to distinguish between the gases from rocks and the gases from biology. Before we jump the gun and talk about astrobiology, we should actually talk about geoastronomy. That’s the big direction I’m trying to push in.