The Birth and Death of Our Solar System: An Interview with Konstantin Batygin

Konstantin Batygin recently joined the Caltech faculty as assistant professor of planetary science, following graduate school at Caltech (PhD '12) and a postdoc at the Harvard-Smithsonian Center for Astrophysics. Batygin was born in Moscow, attended elementary and middle school outside Tokyo, and moved to San Jose while in high school. He chose UC Santa Cruz for college to be near the beach and to continue playing with the band he had formed in high school. He decided to major in astrophysics the day before classes started his freshman year.

It's a decision Batygin has never regretted. Early in his undergraduate career, a mentor started Batygin thinking about the fate of our solar system. From there, one question led to another and another, and now Batygin works on everything from the evolution of our solar system to the weather on exoplanets.

Batygin recently spoke about the string of synchronicities that brought him to planetary astrophysics and to Caltech.

How did you find your way into astrophysics and planetary science?

I applied to UC Santa Cruz as an engineering major. On registration day, I had to go pick up a piece of paper from some office, and there was a guy there. I don't know if he was a student or what. But he said to me, "Yo dawg, what's your major?" I told him it was engineering. And he said, "You should do astrophysics. It's dope." As I left the office, I thought, "Wow, astrophysics does sound totally dope." So I went to the physics department and changed my major.

When did you develop an interest in planetary science?

Planetary science wasn't in my plan. I wanted to do high-energy astrophysics. But then at a department party I met Greg Laughlin, a planetary scientist at UC Santa Cruz. He's a very creative guy and an expert in chaos theory. He suggested that we might try to figure out what the long-term fate of our solar system would be. I thought to myself, "Surely someone like Newton must have solved that problem already." But I was wrong about that. As soon as we started working on this stuff, I just fell in love with it. It's a very counterintuitive situation. You tend to think that the motion of the planets is like clockwork, where things keep going around in an orderly fashion. You only need one physics law—gravity—to predict the basic motions of the planets. But it's actually a very complicated problem.

In what way?

Part of it is pretty easy. For the numerical simulations involved, any reasonably astute graduate student could do the work. The more difficult part of the problem is trying to explain what we find in the numerical simulations. For example, the simulations reveal that if you wait long enough, Mercury will leave the solar system. It will become unstable, its orbit will become unbound, and it will take off.

Really? Even though it's the closest planet to the sun, it just flies off rather than falling into the sun?

Yes. It's called chaotic diffusion. This happens over a multibillion-year timescale. Planetary orbits are a little bit like weather. We can't predict the weather for longer than three days. But we can generally expect that the weather is not going to change by thousands of degrees; it's going to be in some bounded range. Planetary orbits are like that. They vary, but they mostly hang out in a well-defined region of phase space. Occasionally, though, they leave that phase space and transition into a different shape. This is why Mercury takes off at some point in the future. It's a beautiful problem. You've got eight members of the system—planets—whose masses are low. But over long time spans, they exchange angular momentum in a deterministic yet unpredictable manner. If you wait long enough, at one point Mercury bites off more angular momentum deficit than it can chew and leaves the solar system.

Why did you choose Caltech for graduate school?

First I got an email from Mike Brown [Caltech's Richard and Barbara Rosenberg Professor and professor of planetary astronomy], saying congratulations, I had been admitted to Caltech. I thought, "Well, this is a funny coincidence, another Mike Brown." Then I realized, "Wait, this is the Mike Brown!" So I came to campus, just for a day, but I immediately knew this was where I would come for graduate school. I have never felt quite as at home as I do at Caltech. That's been true from the first moment.

Why do you think you had such an instant affinity for Caltech?

Southern California is pretty awesome, so there's that. But I think Caltech has a unique aura, and I think that has to do with quality. It is the pursuit of quality rather than quantity, so to speak. And that's basically why we do science.

Had you completed your work on the long-term fate of our solar system before you came to Caltech for grad school?

Yes, but I've actually gone back and revisited that problem. We've tried to put ourselves in a time before computers were around, and ask what we learn about orbits in our solar system if we don't assume that everything works like a clock, to ask if we can get at the numerically obtained results with perturbation theory. We're hoping to proceed entirely analytically, getting to the underlying physical structure of dynamic instability.

Newton was working with an assumption of clockwork motion?

No, when Newton came out with his law, he himself didn't believe that the solar system would be stable. He believed that gravity would gradually unravel it, and that God would have to come in and reset it. The idea of perfect determinism was introduced later by Laplace, among others. We're seeing the same instability, but looking at secular solutions to the problem of what happens to the solar system over time.

What are you working on now?

In effect I'm continuing all the projects that I've started up until now. When I came to Caltech as a grad student I was pretty comfortable with working on the dynamics of the solar system. But then Dave Stevenson [the Marvin L. Goldberger Professor of Planetary Science] shattered my world by opening up a whole set of other interesting problems in planetary science. And Mike Brown and I worked on the solar system, but we examined the beginning rather than the end. The early evolution of the solar system is also very wild and chaos-dominated. I also ended up working on the interiors of exoplanets and the formation of the Kuiper belt, and at Harvard I worked on the evolution of protoplanetary disks and the weather on exoplanets.

Do you observe the planets directly, or do you use other people's observations?

No, I don't observe. I should not be allowed near a telescope. I have great respect for observers, but it doesn't come naturally for me. You have to be really focused. I don't have observing capabilities.

Have you found a band to play with since you got back from your postdoc in the Boston area?

Yes, my band, the Seventh Season, keeps remaking itself. You can find our music on iTunes. Once in a while we get a check from iTunes for $20 or so. We're working on two new albums now. They're untitled. We're open to suggestions.

And do you still like the beach?

I haven't been surfing yet, but we went to the beach last weekend. My daughter loved the water. It was a scandal when I tried to take her out after an hour in the ocean.