How I Killed Pluto and Why It Had It Coming - Hardcover

A Letter from Author Mike Brown

My daughter Lilah, now five years old, is mad at me for killing Pluto. When I began a project 13 years ago to chart the slowly-moving objects of the distant outer solar system, my goal was never to pull Pluto off of its cherished planetary pedestal. I wanted to be a planet discoverer, like William Herschel or Clyde Tombaugh before me. I had a strong feeling that somewhere out there something bigger than Pluto was lurking, and I knew that whoever found it would get to claim the mantle as the only living planet discoverer.

I was right. Something bigger than Pluto was out there (or at least something more massive than Pluto; sizes are a little harder to pin down precisely) and one January morning in 2005, my small team of astronomers and I found it. We announced the discovery of the 10th planet to an unsuspecting world late on the afternoon of Lilah’s 22nd day of life. A little after her first birthday, though, the doors to the planetary club were locked and Pluto and my own discovery were kicked out on the curb. The solar system was down to only eight planets.

It was hard not to mourn the loss of my now ex-planet, except for the fact that I had to admit that kicking it out was the most scientifically sensible thing to happen to planetary classification since asteroids were also kicked out almost 200 years ago. The solar system is a beautiful and profound place, and it is made richer with the realization that the eight planets are the foundation throughout which countless smaller bodies continuously swirl.

When Pluto was first demoted, people said to me, “What about the children? How could you do this to them?” But, in fact, children live lives that are always changing. It’s the adults who have had the hardest time reconciling the new understanding of the solar system with what they remember from when they themselves were children. So, it made sense that I used to joke about what would happen the moment when Lilah first learned about the solar system. She would come home, and I would say, “Tell me all about the eight planets,” and when I would try to tell her about the olden times when we used to think there were nine—or even ten!—planets, she would slowly shake her head and exclaim, “Daddy, adults are so stupid.”

But I was wrong.

Lilah knows all about Pluto. She has a stuffed dog, a planet lunch box, a solar system place mat at the dinner table. She feels as warmly towards the ice ball as someone ten times her age, and, like many of those older people, she is mad at the person who killed it. Lilah, though, has a solution. She recently told me, “Daddy, I know that you had to kill Pluto, but will you promise me one thing?”

“Of course,” I said.

“You have to go find another planet, and when you do, you have to name it Pluto for me, OK?”

So my search of the skies continues.

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. He lives in Southern California with his wife and daughter.