How I Killed Pluto and Why It Had It Coming

We all grew up learning, in school, that there were nine planets in the solar system. We never thought much about it: That's just the way it was. But in 2005, Mike Brown, a professor of planetary astronomy at the California Institute of Technology, discovered a tenth. As he explains in his new book, How I Killed Pluto and Why it Had it Coming, out today by Spiegel & Grau, this is something he had been working toward his whole life. That day of discovery was one of the best days of his life, second only, perhaps, to the day his daughter, Lilah, was born.

But the excitement only lasted so long. Brown's discovery ignited a year-long debate over how, exactly, to define a planet. And when things got out of control, when too many bodies were being upgraded to planetary status, it was Brown who had to step in and demote his own discovery, the largest object found in the solar system in 150 years, and, along with it, beloved Pluto.

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I couldn't accept it.

The solar system does not consist of twelve planets and then everything else. That is simply a fundamentally incorrect description of it. And the next day in Prague, astronomers were going to stand up and encourage the world to think of the solar system incorrectly. As someone who spends much of my life trying to be not just a scientist but an educator, trying to explain the universe and show the excitement without resorting to science fiction or trivial simplification, the idea that astronomers would actively encourage people to have the wrong view of the solar system seemed almost criminal. The idea that I was going to, overnight, become one of the most famous astronomers in the world on account of this criminal activity made me a passive accomplice. I had to do something to stop it.

I hobbled back from the rocky beach up to the house. I woke Diane and told her that when the press called tomorrow I was going to have to tell them why the new proposed definition of planet was no good and why, in the end, it made sense all along for there to be just eight planets. I told her that I was going to have to kill Pluto and that Xena would go down as necessary and important collateral damage.

All along, Diane had been more practical than I was. "Just let it be a planet," she would say. "Try not to worry about it so much," she had told me all year. "Relax" was her usual advice.

But this time, when I told her that I couldn't support Xena's becoming a planet, Diane simply said, "Of course not, sweetie. You always needed to do what's right." And then she gave me her usual advice: "Relax."

I did not sleep well that night.

The next morning, I went to the village of Eastsound, where I knew I could get freshly brewed coffee and a freshly flown-in newspaper. On the front page, a headline screamed, "Three New Planets Added to Solar System." A beautifully prepared graphic -- courtesy of the IAU -- showed the new solar system with the twelve planets all in place. The article prominently featured quotes of mine from previous interviews about the new planet Xena.

I felt sick to my stomach.

This was it. Astronomers had taken a beautiful and subtle solar system and turned it into a cartoon. And the cartoon was wrong.

I went back to the house and called the people at media relations at Caltech and told them where to find me. I hung up the phone and waited for two minutes before it rang.

I spent most of the next twelve hours, and indeed most of the next week, on the phone talking to the press about the solar system, planets, and why the IAU's proposed definition was fatally flawed, and explaining why Pluto -- and Xena -- should really not be considered planets.

At first the reporters were shocked. They were calling to get quotes from the most newly minted planet discoverer about how fabulous all of this was. Instead I was telling them that everything they had heard from the IAU the day before made no sense. Suddenly there was a controversy. My phone kept ringing.

Lilah developed a new sign, which either meant "Daddy" or simply meant "phone," I could never tell. Whenever she saw an object of the right size, she would pick it up and immediately hold it to her ear and then point at me.

Astronomers around the world picked up on some of the silly implications of making Charon a planet simply by virtue of the location of the center of mass of the orbit. In the middle of one phone interview, it suddenly occurred to me that the center of mass of the sun and Jupiter lies outside the sun, so by IAU logic, Jupiter should not be considered a planet since it doesn't really go around the sun. Another astronomer sent an email showing that if a massive moon were on an elongated orbit, the center of mass could be inside the planet during part of its orbit but outside the planet during other parts of its orbit, meaning that, according to the IAU, that moon would switch back and forth between being a planet to being a nonplanet during the course of its orbit. And a few days later, courtesy of a fabulous press release by Greg Laughlin, an astronomer at the University of California Santa Cruz, the newspapers explained that because our moon is slowly moving outward, away from the earth, in a billion years or so it will have moved so far away that the center of mass of the earth-moon system will lie outside the earth. Suddenly: boom! The moon will officially be a planet. It would be a day to celebrate.

I wasn't in Prague, so someone else will have to tell the details of what actually happened there. What I do know is this: Astronomers there, who I had been told were going to go along sheepishly with this mess of a proposal, revolted.

The revolting astronomers, who grew to be a sizable fraction of the astronomers present, made it quite firmly known that they would not support the secret committee proposal. The only proposal they would support would be one where Pluto was put in its logical -- rather than emotional -- place. Pluto, Charon, Ceres, and my own Xena would all have to go. The press, and indeed the astronomers in Prague themselves, were quite amused by the fact that one of the most vocal supporters of demoting Pluto, Charon, Ceres, and Xena was the guy who had the most to personally gain from Xena being a planet: me.

Excerpted from the book HOW I KILLED PLUTO AND WHY IT HAD IT COMING by Mike Brown. Copyright 2010 by Mike Brown. Reprinted by arrangement with Spiegel & Grau, an imprint of The Random House Publishing Group, a division of Random House, Inc. All rights reserved.

Image: Computer-generated impression of the Plutonian surface, Wikimedia Commons.