Interview: Mike Brown, author How I Killed Pluto and Why It Had It Coming


The solar system most of us grew up with included nine planets, with Mercury closest to the sun and Pluto at the outer edge. Then, in 2005, astronomer Mike Brown made the discovery of a lifetime: a tenth planet, Eris, slightly bigger than Pluto. But instead of its resulting in one more planet being added to our solar system, Brown’s find ignited a firestorm of controversy that riled the usually sedate world of astronomy and launched him into the public eye. The debate culminated in the demotion of Pluto from real planet to the newly coined category of “dwarf” planet. (from “About the Book“,

Author, astronomer, and lecturer Mike Brown took some time out of his day to discuss his book, astronomy, and what it might be like to attempt to pilot through an asteroid field. Are you ready to find out what it was like to be in the center of “the biggest astronomical cat-fight of the past 200-300 years”?

Let’s find out, shall we?

Let’s start off with a little about the book: The title might be a dead giveaway, but could you describe the book? What led you to write it?

It’s a love story. But nobody else other than me would describe it like that. It’s got a provocative title and you might think it’s about me being happy that Pluto died. But it’s really a long process that led to Pluto not being a planet and one that I wasn’t always happy about. And in the end I think it had it coming, but it doesn’t mean that in the end you’re happy about it. But it’s the story of that and what it’s like to be in the middle of the biggest astronomical catfight of the past 200-300 years.

How I Killed Pluto and Why It Had It Coming isn’t a hefty scientific book targeted only at PhD students; it’s a blend of history, science, and memoir. Who do you see as the ideal audience for this book?

I like to think of it as a book for anybody. Certainly people who are interested in Pluto and astronomy will pick it up and want to learn about the science and discoveries going on. But it’s not a “science” book; I like to think of it as nonfiction-personal essay that has a subject of science, but also life and childhood and what it’s like to be a father.

You’re a “planet guy” but as we see throughout the course of this book, deciding what a planet is and a planet isn’t can be a mighty chore. So, here’s the million-dollar question: What is a planet anyway?

The easiest way to describe a planet? In the entire field of astronomy, there is no definition of what things are; we work on “concepts” so the easiest way to think of a planet is that it is a large, important thing orbiting a star. So, in the solar system, if you look at it, it becomes incredibly obvious that these eight things that we call planets orbit the sun and dominate the area in which they orbit, and there are thousands of tiny things that don’t, as individuals, make much difference in the solar system, like Pluto.

But it’s the story of that and what it’s like to be in the middle of the biggest astronomical catfight of the past 200-300 years.

In Chapter 11, “Planet or Not” (page 182) you write:

“[…] all spring I had been trying hard to understand how we should define the word planet.

I asked an old college friend with a PhD in philosophy: What does a word mean when you say it?

“Words mean what people think they mean” was his smoothly philosophical reply. “So when you say ‘planet’ it means what you are thinking when you say it.”

Not exactly hard science there, but not entirely untrue either. Does this relegate the whole planet-or-not discussion as moot?

No, I think of it as the opposite. That is, in some ways, the most profound statement, because when people say the word “planet,” they have a picture in their mind about a small number of important objects going around a star. You’re probably not talking about all these minor things going around the solar system.

Our job as astronomers wasn’t to define “planet” but to discover what it meant and use it properly. Even though the public was against the idea of eliminating Pluto, it was because they didn’t have an accurate idea of how big or important to the solar system Pluto really is.

Do you worry that these cool scientific discoveries of other big objects are getting lost in a discussion about semantics?

I’m still sad about that; it really is true. I wish we could have moved on from the discussion of “what is a planet and what isn’t” and say, “Wow, look at all the cool science going on out there!” I still go around to academic departments giving talks about the science going on behind and around these discoveries and people are still amazed that all this science is going on behind it. If people had just let go after Pluto was demoted, we might have been able to dive into these things more than we did at the time.

I’ve heard Neil deGrasse Tyson speak about the demoting of Pluto and removing it from the Hayden Planetarium planet display and he always mentions the outrage expressed by schoolchildren. Did you experience a similar reaction?

Oh yeah, I have stacks of hate mail. Most of it from schoolkids (though some from scientists attached to the New Horizons mission) and these days, schoolkids know enough about e-mail to send hate e-mail as well. Some are cute, but others make you cringe at the level of personal vehemence that some fifth-graders think are okay to send to strangers. You have to keep your sense of humor.

Now if you talk to a third-grade class today and try to tell them that there are nine planets, they’ll shout you down and say, “No, there are only eight.” It’s the students and adults who learned that there were nine planets as schoolchildren that are having difficulty with it now.

I wish we could have moved on from the discussion of “what is a planet and what isn’t” and say, “Wow, look at all the cool science going on out there!”

Speaking of talking to children about how many planets there are, you have a section in your book where you talk about a choreographed Q&A that you and your daughter, who was then a very young child, would perform when asked about Pluto’s demotion. You then imagine that later on, when told that there was once a time when people thought there were nine or even ten planets, she might respond, “You know, adults are so stupid.” Has that come to fruition?

You know, she’s actually a little mad at me about Pluto now. You see, she’s heard it said so often that her father is the guy who “killed Pluto,” and killing is bad, that she’s been a little upset about it. But she’s also told me that to make up for it, I have to discover a planet bigger than Pluto and name that planet Pluto. We’ll see.

When you discovered Planet Xena, were you expecting it to knock Pluto out of planethood?

No, I really didn’t. I honestly expected that it would be declared the tenth planet. I really — I’m still amazed to this day — thought that astronomers didn’t have the guts to talk about what is a planet and what isn’t, because it would be really unpopular. The only reason that it happened, as far as I can tell, was the bizarre set of events that culminated in the big meeting of astronomers with all the crazy personalities that led to it.

I think in the end, it was all the craziness associated with the calls to keep Pluto that helped fuel the fire to further the discussion, which eventually lead to the demotion of Pluto to a dwarf planet. And I was shocked.

But that said, I’m much, much happier to be the discoverer of the biggest dwarf planet known today than to be the discoverer of the fraudulent tenth planet.

As we might expect, the Kuiper Belt plays a role in defining Pluto. These sorts of belts also frequently play a role in space films and novels as hazardous areas or places to hide. What might we actually see if we were to navigate a space vessel into a place like the Kuiper Belt?

I can answer that easily for the asteroid belt between Mars and Jupiter, as objects are closer together. So you have your picture of Han Solo looking around for places to hide. In reality, we have navigated objects through our own asteroid belt to get to Jupiter. Not until the Voyager project did we actually try to target an asteroid. To do this there were an incredible amount of calculations, re-calculations, adjustments, and there was still the possibility that we’d miss one. The reality is that if you try really, really hard you can probably get close to one if you know where it is.

Now as to the Kuiper Belt: The hope is that after New Horizons flies past Pluto, we’ll find a target in the Kuiper Belt that we could study in a similar fashion, but there’s no guarantee that there will be an object out there within our capabilities to find and target.

But she’s also told me that to make up for it, I have to discover a planet bigger than Pluto and name that planet Pluto. We’ll see.

You get to work with the most incredible telescopes in use today. What does it really look like when you’re looking through a big telescope?

These days all the pictures that you see through a telescope, you’re looking at digital pictures of what is being seen. In some ways, you might think that loses some of the romance of looking directly through the telescope at the sky. And while that’s true, I remember the first time I viewed an image of Eris on the digital screen and I was so excited about the discovery that the fact that it was a digital image never crossed my mind.

Let’s wrap up with a little star (or planetary) gazing. If we were looking for something cool in the night sky right now, or in the near future, what should we look for?

It’s the jewel of the night sky and it’s up right now and will be beautiful for the next few months: Jupiter. Go outside, look south after sunset and it’s obvious. It’s the super-bright thing in the sky that you might think is an airplane. But the best possible way to see it is to view it with binoculars and you can see those four moons that Galileo discovered. If you look at them each night, they’ll be in a different position and it’s really cool.

You can see the moons of Jupiter and the rings of Jupiter and it’s there and it’s real and not just pictures from NASA! It’s such a cool thing to see and almost everyone has the ability to see it; yet so few people ever do.

Photo: Mike Brown. Copyright Bob Paz

Photo: Mike Brown. Copyright Bob Paz

Mike Brown is the Richard and Barbara Rosenberg Professor of Planetary Astronomy at the California Institute of Technology. In 2006 he was named one of Time magazine’s 100 People Who Shape Our World as well as one of Los Angeles magazine’s Most Influential People in L.A, and Wired Online’s Top Ten Sexiest Geeks of 2006. He lives in Southern California with his wife and daughter.