How I Killed Pluto and Why It Had It Coming

  Copyright © 2010 by Mike Brown

  All rights reserved.

  Published in the United States by Spiegel & Grau, an imprint of The Random House Publishing Group, a division of Random House, Inc., New York.

  SPIEGEL & GRAU and Design is a registered trademark of Random House, Inc.

  Library of Congress Cataloging-in-Publication Data

  Brown, Mike.

  How I killed Pluto and why it had it coming / Mike Brown.

  p. cm.

  eISBN: 978-0-385-53109-2

  1. Pluto (Dwarf planet). 2. Planets. 3. Solar system. 4. Discoveries in science—

  Anecdotes. I. Title.

  QB701.B77 2010

  523.49′2—dc22 2010015074

  www.spiegelandgrau.com

  v3.1

  For Diane and Lilah

  Prologue

  PLUTO DIES

  As an astronomer, I have long had a professional aversion to waking up before dawn, preferring instead to see sunrise not as an early-morning treat, but as the signal that the end of a long night of work has come and it is finally time for overdue sleep. But in the predawn of August 25, 2006, I awoke early and was up sneaking out the door, trying not to wake my wife, Diane, or our one-year-old daughter, Lilah. I wasn’t quite quiet enough. As I was closing the front door behind me, Diane called out, “Good luck, sweetie!”

  I made the short drive downhill through the dark empty streets of Pasadena to the Caltech campus, where I found myself at 4:30 a.m., freshly showered, partially awake, and uncharacteristically nicely dressed, unlocking my office building to let in news crews that had been waiting outside. All of the local news affiliates were there, as well as representatives of most of the national networks. Outside, a Japanese-speaking crew was pointing a TV camera up at the sky, the beams of the flood lamps disappearing into space.

  Today was the last day of the International Astronomical Union meeting in Prague, and the final item on the agenda at the end of two weeks’ worth of discussion was a vote on what to do with Pluto. Everyone’s favorite ice ball was in imminent danger of being cast out of the pantheon of planets by the vote of astronomers assembled half a world away, and whatever happened would be big news around the globe.

  I like planets, but I didn’t care enough about Pluto to get up at 4:30 a.m. But this Pluto vote mattered enough for me to drag myself out of bed that morning. For me that vote had nothing to do with the ninth planet; it was all about the tenth. And I cared a lot about that tenth planet, because eighteen months earlier, I had discovered it, a ball of ice and rock slightly larger than Pluto circling the sun every 580 years. I had been scanning the skies night after night looking for such a thing for most of a decade, and then, one morning, there it finally was.

  At the time of the Pluto vote, my discovery was still officially called only by its license plate number of 2003 UB313, but to many it was known by the tongue-in-cheek nickname of Xena, and to even more it was known simply as the tenth planet. Or maybe, after today, not the tenth planet. Xena had precipitated the past year of intensive arguments about Pluto, but it was clear that Xena would share whatever fate was dealt to Pluto. If Pluto was to be a planet, then so too Xena. If Pluto was to be kicked out, Xena would get the same boot. It was worth waking up early to find out the answer.

  The previous two weeks in Prague had been perhaps the most contentious gathering in modern astronomical history. Usually the International Astronomical Union meeting is nothing but a once-every-three-years chance for astronomers to advertise their latest discovery or newest idea while spending some time in a nice international destination, having dinners with old friends and catching up on their celestial gossip. On the final day of each meeting, in a session attended by almost no one, resolutions are passed, usually all but unanimously, on such pressing topics as the precise definition, to the millisecond, of Barycentric Dynamical Time (I have no idea what this actually even means).

  This year was different. The usually placid astronomers had spent their time in Prague arguing and bickering day and night about Pluto and about planets. While several of the typically unintelligible resolutions were indeed to be voted on this last day, the final two resolutions would be all about Pluto. The usually sparsely attended final session was likely to be full of surly astronomers itching for a fight.

  While the astronomers were gathering for their vote in Prague, the news crews and I were arriving in the early morning on the Caltech campus in Pasadena, California, so that we could watch the excitement via a webcast. My job was to provide commentary and analysis for the press and moral support and scientific coverage for the astronomers who were—rightly, I thought—trying to take the bold move of ridding the solar system of the baggage of planet Pluto. I found the webcast, projected it on the large screen, and we all sat back to watch.

  Three mostly esoteric and tedious hours later, it was all over. On the final vote, the air was filled with yellow cards with which the astronomers in Prague were voting “no” to Pluto’s planethood. There was no need to count; the vote was not even close. After hours of detailed explanation and analysis and discussion of the subtleties of all the different possible outcomes, I could finally just say: “Pluto is dead.”

  The cameras whirred; correspondents talked into their microphones, and on a screen on the other side of the room, I could see myself on some local television station repeating, like an echo, “Pluto is dead.”

  Before anyone else could ask a question, I quickly picked up the phone and called Diane, who was now at work. I had made a similar phone call eighteen months earlier, only minutes after I had discovered Xena. Back then, the moment she picked up the phone I said, “I found a planet!”

  Back then, her voice had risen. “Really?”

  Yeah! Really!

  This time, instead, the moment she picked up the phone, I said, “Pluto is no longer a planet!”

  Her voice dropped. “Really?”

  Yeah! Really! I was still excited about the vote and had not quite grasped her mood.

  She paused for a long time. “And Xena?” she finally asked quietly.

  But Diane already knew the answer. Xena had indeed gotten the same boot as Pluto, and Diane was already mourning the little planet that we had gotten to know so well.

  In the days that followed, I would hear from many people who were sad about Pluto. And I understood. Pluto was part of their mental landscape, the one they had constructed to organize their thinking about the solar system and their own place within it. Pluto seemed like the edge of existence. Ripping Pluto out of that landscape caused what felt like an inconceivably empty hole.

  That first morning, Diane was having the same reaction, but for Xena instead of Pluto. For her, Xena was more than just that thing that used to be called “the tenth planet.” She had listened to me enough over the previous eighteen months that she had gotten to know all about the onetime tenth planet. She knew about its tiny moon, its incredibly shiny surface, and its atmosphere frozen in a thin layer all around the globe. Diane and I had discussed the excitement of the search, what to name the tenth planet, and how many more like it might be out there. Xena had become as much a part of our own mental landscapes as Pluto might have been for anyone else. And Xena would be forever linked in our minds to our daughter, Lilah, who was only three weeks old when Xena was announced to the world. All of those memories of the first months of our Lilah’s life—the lack of sleep, the dazed confusion, the questions about what life would be like after this sudden change—were tied up with all of our memories of what became tenth-planet mania—the rush to learn more, the push to discover others, the questions about what life would be like after th
is sudden change. And now, just a little after Lilah’s first birthday, Xena was gone.

  I had to tell Diane: The astronomers did the right thing.

  Xena is not really gone, of course. It is now actually the largest of the dwarf planets, which it rightfully deserves to be.

  Lilah will probably not learn about Xena in school, but someday, we’ll tell her that when she was three weeks old the world first heard about the tenth planet, and we’ll pull out our little box of Xena news clippings and talk about that year when Lilah and the tenth planet were both burning themselves into our lives as things that we could never again imagine the universe without.

  CONTENTS

  Cover

  Title Page

  Copyright

  Dedication

  Prologue: Pluto Dies

  1 What Is a Planet?

  2 A Millennium of Planets

  3 The Moon Is My Nemesis

  4 The Second-Best Thing

  5 An Icy Nail

  6 The End of the Solar System

  7 Raining = Pouring

  8 Lilah, an Intermission

  9 The Tenth Planet

  10 Stealing the Show

  11 Planet or Not

  12 Mean Very Evil Men

  13 Discord and Strife

  Epilogue: Jupiter Moves

  Acknowledgments

  About the Author

  Chapter One

  WHAT IS A PLANET?

  One December night in 1999, a friend and I were sitting on a mountaintop east of San Diego inside a thirteen-story-tall dome. Only a few lights illuminated the uncluttered floor of the cavernous interior, but above you could vaguely see the bottom half of the massive Hale Telescope at Palomar Observatory. The Hale Telescope was, for almost fifty years, the largest telescope in the world, but from where we sat, with the weak yellow incandescent lighting being swallowed in the darkness above, you would never have guessed where you were. You might have thought you were deep in the interior of a pristine Hoover Dam, with cables and wire and pipes for directing the flow of water around. You might have believed that the steel structures around you were part of the far underground support and control of a spotlessly clean century-old subway system. Only when the entire building gently rumbled and a tiny sliver of the starry sky appeared far over your head and the telescope began to move soundlessly and swiftly to point to some new distant object in the universe, only then would you be able to make out the shadowy outline of the truss all the way to the top of the dome and realize that you were but a dot at the base of a giant machine whose only purpose was to gather the light from a single spot beyond the sky and focus it to a tiny point just over your head.

  Usually when I am working at the telescope I sit in the warm, well-lit control room, looking at computer screens showing instrument readouts, staring at digital pictures just pulled from the sky, and pondering meteorological readings and forecasts for southern California. Sometimes, though, I like to step out into the cold, dark dome and stand at the very base of the telescope and look up at the sky through the tiny open sliver high overhead and see—with my own eyes—exactly what the giant machine is looking at. This December night, however, as I was sitting with my friend inside the dark dome, there was no sky to see. The dome was fastened closed, and the telescope was idle because the entire mountain was covered in cold, dripping fog.

  I tend to get quite glum on nights when I’m at a telescope with the dome closed and the precious night is slipping past. An astronomer gets to use one of these biggest telescopes only a handful of nights per year. If the night is cloudy or rainy or snowy, too bad. Your night on the telescope is simply lost, and you get to try again next year. It’s hard not to think about lost time and lost discoveries as the second hand very slowly crawls through the night and your dome stays closed. Sabine—my friend—tried to cheer me up by asking about life and work, but it didn’t help. I instead told her about how my father had died that spring, and how I felt unable to really focus on my work. She finally asked me if there was anything that I was excited about these days. I paused for a few minutes. I momentarily forgot about the freezing fog and the closed dome and the ticking clock. “I think there’s another planet past Pluto,” I told her.

  Another planet? Such a suggestion would have generally been scoffed at by most astronomers in the last days of the twentieth century. While it is true that for much of the last century astronomers had diligently searched for a mythical “Planet X” beyond Pluto, by about 1990 they had more or less convinced themselves that all that searching in the past had been in vain; Planet X simply did not exist. Astronomers were certain that they had a pretty good inventory of what the solar system contained, of all of the planets and their moons, and of most of the comets and asteroids that circled the sun. There were certainly small asteroids still to be discovered, and occasionally a bright comet that had never been seen before would come screaming in from the far depths of space, but certainly nothing major was left out there to find. Serious discussions by serious astronomers of another planet beyond Pluto were as likely as serious discussions by serious geologists on the location of the lost continent of Atlantis. What kind of an astronomer would sit underneath one of the biggest telescopes in the world and declare, “I think there’s another planet past Pluto”?

  • • •

  Almost a decade earlier, in the late summer of 1992, I was in the long middle years of my graduate studies at Berkeley (the place where I was taught that Planet X certainly did not exist and that we already knew pretty much everything we needed to know about what there was in the solar system). I didn’t think much about Planet X those days. I was midway through a Ph.D. dissertation about the planet Jupiter and its volcanic moon Io. When you’re midway through a Ph.D. dissertation, your mind acquires narrow blinders, so I didn’t think much about anything other than Io and how its volcanoes spewed material into space and affected Jupiter’s powerful magnetic field. I had so few thoughts to spare for most of the quotidian universe that I had fallen into a pattern of every day eating the same lunch at the same coffee shop right next to the Berkeley campus and having dinner at the same burrito stand a block away. At night I would ride my bicycle back down toward the San Francisco Bay to the marina where I lived on a tiny sailboat. The next morning I would start all over again. Less time thinking about what and where to eat and sleep meant more time thinking about Io and volcanoes and Jupiter and how they all fit together.

  But, occasionally, even obsessive Ph.D. students need a break.

  One afternoon, as on many times previous, after spending too much time staring at data on my computer screen and reading technical papers in dense journals and writing down thoughts and ideas in my black bound notebooks, I opened the door of my little graduate student office on the roof of the astronomy building, stepped into the enclosed rooftop courtyard, and climbed the metal stairs that went to the very top of the roof to an open balcony. As I stared at the San Francisco Bay laid out in front of me, trying to pull my head back down to the earth by watching the boats blowing across the water, Jane Luu, a friend and researcher in the astronomy department who had an office across the rooftop courtyard, clunked up the metal stairs and looked out across the water in the same direction I was staring. Softly and conspiratorially she said, “Nobody knows it yet, but we just found the Kuiper belt.”

  I could tell that she knew she was onto something big, could sense her excitement, and I was flattered that here she was telling me this astounding information that no one else knew.

  “Wow,” I said. “What’s the Kuiper belt?”

  It’s funny today to think that I had no idea what she was talking about. Today if you sat next to me on an airplane and asked about the Kuiper belt, I might talk for hours about the region of space beyond Neptune where vast numbers of small icy objects circle the sun in cold storage and about how, occasionally, one of them comes plummeting into the inner part of the solar system to light up the skies like a comet. I might talk about the very edge o
f the solar system, where millions of little icy bodies never quite got gathered up into one big planet but instead stayed strewn in the disk surrounding the solar system. And I might tell you a little history, about how in the early 1990s no one had seen such a thing as this Kuiper belt, but a small group of astronomers who had predicted its existence had named the region the Kuiper belt after Dutch American astronomer Gerard Kuiper, who had speculated about its existence decades earlier. And finally, if you were still listening and the plane had not yet landed, I would tell you how this Kuiper belt was finally seen, for the first time, in the late summer of 1992, and how I first learned about it on the roof of the Berkeley astronomy building a day before it appeared on the front page of The New York Times.

  But when Jane told me she had just found the Kuiper belt, I didn’t know any of this. Jane explained. She had not found this vast collection of bodies beyond Neptune, exactly, but simply a single small icy body circling the sun well beyond the orbit of Pluto. The body was tiny—much, much smaller than Pluto—and as far as anyone knew for sure, it might have circled the sun all alone at the edge of the solar system. But still, exciting, right?

  Cute, I thought. But it’s just one tiny object, and it’s farther away than Pluto. How could that matter?

  So I nodded and listened and, like any diligent Ph.D. student midway through a dissertation, eventually walked back down the stairs, stepped into my office, and reentered the world of Jupiter and Io and volcanoes, where I actually resided.

  I was wrong, of course. Even though the object discovered was only a lonely, relatively tiny ball of ice orbiting beyond Pluto, it showed that astronomers had been wrong: They didn’t actually know everything; there were things still to be found at the edge of our own solar system. Some astronomers were reluctant to consider this new possibility seriously, and they dismissed the discovery as nothing more than a fluke that presaged absolutely nothing. But soon, as more and more astronomers became excited about the possibility of discovery and started searching the regions beyond Pluto, more and more of these small bodies began to be found.