A year earlier, when the existence of Xena was first announced, I had considered naming the potentially tenth planet after Lilah in some way. Diane had dissuaded me.

"What if we have a second child and you never find another planet?" she said.

That was a convincing argument.

I told her she should take the moon naming as a good sign: While it was possible that we might had a second child, there would be only one wife!

"Um, thanks, I think," said Diane, again.

Many people know about the Rose Parade, which winds through Pasadena every New Year's Day just as it did four days before the discovery of Eris in 2005. Less well known is the yearly alternative version of the Rose Parade called the Doo Dah Parade, which goes along some of the same main parade route as the Rose Parade. It attracts large crowds and features things such as marching toilets, a Doo Dah Queen (usually in drag), flying tortillas, and a Precision Grill team, cooking up barbecue along the way. In 2006, it also featured a New Orleans Jazz Funeral for Pluto organized by some local astronomers with a sense of humor. The eight planets were each represented by a costumed astronomer with a large cardboard name tag hanging around his or her neck. They carried Pluto in a casket to sounds of New Orleans jazz. The astronomers invited me to partic.i.p.ate and gave me a cardboard name tag that read: "Mike Brown: Pluto Killer." I had agreed to march in the parade on one condition: that Eris also be invited. Eris, played by Lilah, was pushed in a stroller down the parade route by her father.

Like most marchers in the Doo Dah Parade, we got quizzical looks, a few claps, a smattering of boos, and a lot of tortillas thrown at us. I spent most of my time trying to make sure Lilah didn't pick them up and eat them. But still, Pluto was dead, and it was good to partic.i.p.ate in its burial.

But not everyone was ready to bury Pluto just yet.

On the very day of the vote to demote Pluto and Eris, a few astronomers began collecting signatures protesting the details of the IAU decision. They issued a simple statement: We, as planetary scientists and astronomers, do not agree with the IAU's definition of a planet, nor will we use it. A better definition is needed.

It's hard to argue with that statement. As much as I am proud of the astronomers who had the guts to go against emotional sentiment and to remake the solar system correctly, the actual definition by which they did it is pretty clunky. In fact, I won't use it, either.

In the question-and-answer session of a recent talk I gave at Sarah Lawrence College, a very agitated young woman raised her hand and began to read from notes: "In the IAU definition of the word 'planet' it says you have to be three things to be a planet..."

"Wait, wait, wait," I said. "Before you even start, let me tell you why you should never never think about the IAU definition of the word 'planet.'" think about the IAU definition of the word 'planet.'"

In the entire field of astronomy, there is no word other than planet planet that has a precise, lawyerly definition, in which certain criteria are specifically enumerated. Why does that has a precise, lawyerly definition, in which certain criteria are specifically enumerated. Why does planet planet have such a definition but have such a definition but star, galaxy star, galaxy, and giant molecular cloud giant molecular cloud do not? Because in astronomy, as in most sciences, scientists work by concepts rather than by definitions. The concept of a star is clear; a star is a collection of gas with fusion reactions in the interior giving off energy. A galaxy is a large, bound collection of stars. A giant molecular cloud is a giant cloud of molecules. The concept of a planet-in the eight-planet solar system-is equally simple to state. A planet is one of a small number of bodies that dominates a planetary system. That is a concept, not a definition. How would you write that down in a precise definition? do not? Because in astronomy, as in most sciences, scientists work by concepts rather than by definitions. The concept of a star is clear; a star is a collection of gas with fusion reactions in the interior giving off energy. A galaxy is a large, bound collection of stars. A giant molecular cloud is a giant cloud of molecules. The concept of a planet-in the eight-planet solar system-is equally simple to state. A planet is one of a small number of bodies that dominates a planetary system. That is a concept, not a definition. How would you write that down in a precise definition?

I wouldn't. Once you write down a definition with lawyerly precision, you get the lawyers involved in deciding whether or not your objects are planets. Astronomers work in concepts. We rarely call in the attorneys for adjudication.

The young woman in the audience was not satisfied.

"You can't just dismiss the definition. The definition is the reason that Pluto is no longer a planet!"

I tried to explain to her that the concept concept, not the definition, is the reason that Pluto is not a planet. The definition was simply a poor attempt at codifying the concept.

She went on: "But by part three of the definition even Jupiter is not a planet!"

The young woman could probably make a reasonable case in court for her strict reading of the definition. But when the case was appealed to the Supreme Court-and it certainly would be-some justices might try to discern the original intent of the definers. I am certain that it was not anyone's intent to exclude Jupiter from being a planet. The original intent was simply an attempt to describe the eight-planet solar system. The case for a strict reading of the definition would ultimately be tossed out. And then, if the justices were wise, they would also toss out the definition altogether. We're better off without one. Pluto is not a planet not because it fails to meet the three-headed criteria laid out by the IAU. Pluto is not a planet because the criteria were written to try to explain the concept that Pluto is not a planet.

But the astronomers who organized the pet.i.tion saying that they would never use the IAU definition were not quibbling over the logic of having a definition in the first place. They wanted the eight-planet solar system overturned. They wanted Pluto resurrected. While most of the rest of the astronomical world has acknowledged the reasonableness of the decision and moved on, a small group is continuing to try to have Pluto make a comeback.

Over the months and years, their arguments have changed, in the attempt to get some traction. At first, they took a line straight from the people trying to get creationism taught alongside evolution in schools: "Teach the controversy!" they said. Then they argued that the IAU decision was undemocratic because many of the members of the IAU had not been there that day to vote. The complaint is true, but the implication that the outcome would have been different is quite a stretch. Sometimes the argument is that only planetary planetary astronomers are qualified to make the decision-again, as if that would make a difference. In my unscientific poll of seven professors of planetary science who happen to work on the same floor as I do, all seven thought that eight planets make the most sense. astronomers are qualified to make the decision-again, as if that would make a difference. In my unscientific poll of seven professors of planetary science who happen to work on the same floor as I do, all seven thought that eight planets make the most sense.

Particularly amusing to me was the complaint about the phrase dwarf planet dwarf planet. By the simple rules of grammar, a dwarf planet is a planet, they would say. The fact that the IAU would say that a dwarf planet is not a planet demonstrates that the entire decision must be wrong. What no one making these arguments remembers-or admits to remembering-is that the only people who liked the phrase dwarf planet dwarf planet at first were the ones who hoped that it would save Pluto when the other planets were renamed "cla.s.sical planets." Yet Resolution 5B was a specific vote on this issue, and it clearly stated that dwarf planets are not planets-just as Matchbox cars are not cars, stuffed animals are not animals, and chocolate bunnies are not bunnies. I don't particularly like the phrase at first were the ones who hoped that it would save Pluto when the other planets were renamed "cla.s.sical planets." Yet Resolution 5B was a specific vote on this issue, and it clearly stated that dwarf planets are not planets-just as Matchbox cars are not cars, stuffed animals are not animals, and chocolate bunnies are not bunnies. I don't particularly like the phrase dwarf planet dwarf planet, either, but it is serviceable.

I've heard the argument that the definition is unworkable because it is inconsistent with the rest of astronomy. Nowhere else in astronomy, some say, do you cla.s.sify an object by its relationship to its neighbors instead of by its own individual properties. Therefore the only definition that makes sense is that all round things are planets, regardless of where they find themselves. Well, not all round things are planets, just round things that orbit stars. And what if the round thing orbits another round thing? Well, then it is a moon, of course. But but but, doesn't that violate the rule that things aren't defined in relationship to other things? Well, yes, but that's just common sense, they would say. Okay. Got it.

A few weeks after Xena became Eris, I received a note from a friend: The Spanish are trying to steal Santa again.

The Spanish? I hadn't thought much about them in the preceeding eighteen months and certainly hadn't heard anything from them. By this time, I was almost able to laugh about the whole incident.

But they were really back.

After the IAU decided to call round things dwarf planets, Easterbunny and Santa were eligible for real names, too, and the Spanish astronomers quickly submitted a name for Santa-because, of course, the discoverers get to name their discovery.

Rumor had it that the IAU was going to act swiftly, so Chad, David, and I quickly consulted and came up with our own name: Haumea, after the Hawaiian G.o.ddess of childbirth. Like the name Eris, the name Haumea seemed almost custom made for this object. The G.o.ddess Haumea gave birth to her many children by breaking them off from parts of her body. Santa the dwarf planet also had many children throughout the solar system that had broken off from its body. It seemed a perfect fit. And whatever the name was, it definitely definitely should not be whatever the Spanish astronomers were submitting! should not be whatever the Spanish astronomers were submitting!

I wrote an impa.s.sioned letter to the various committees of the IAU proposing the name Haumea and also proposing names for two moons: Hi'iaka, the patron G.o.ddess of the Big Island, and Namaka, a water spirit, both daughters of Haumea. In the letter, I laid out-once again-all that had transpired. And then I explained why it was important that the IAU choose wisely which name to use. There was no question that eighteen months earlier someone had done something unseemly. If the Spanish astronomers had fraudulently claimed discovery of something that they had never actually discovered, it would be appropriate for the IAU to condemn such a thing. If, on the other hand, their discovery was legitimate, they should be exonerated and I should be censured for making a spectacularly damaging wrongful accusation. Through choosing a name, the IAU would be officially choosing a side. I thought that the members of the IAU would not want to take sides and would instead pick a name themselves. I urged them not to cop out. No one else had the authority to render any type of meaningful verdict.

I sent in my letter and waited to see what would happen.

And I waited.

Lilah's second birthday came around.

And I waited.

Lilah's third birthday came around.

I was hoping that the IAU was taking its job quite seriously and had launched a multiyear investigation into what had happened. Apparently not. My inside sources tell me that nothing happened that entire time. Finally I got a tip that making a decision about Santa was just too hard and that perhaps we should try giving a name to Easterbunny as a way of getting things restarted.

Ah, Easterbunny. I had been thinking about it now for years. The names Sedna and Orcus (another large Kuiper belt object that we had turned up) had fit the characteristics of the objects' orbits, and the names Eris and Haumea had practically fallen out of the sky at us. Even Quaoar, we felt, was a nice tribute to local mythology.

But what about Easterbunny? Unlike Santa, which has so many interesting characteristics that there were many possible names, Easterbunny has no obvious hook. Its surface is covered with large amounts of almost pure methane ice, a consequence of the fact that it is just a little smaller than Pluto and lacks enough gravity to hold a substantial nitrogen atmosphere, which is scientifically fascinating and all (really, it is) but not easily relatable to terrestrial mythology. For a while I was working on coming up with a name related to the oracles at Delphi: Some people interpret the reported trancelike state of the oracles to be related to natural gas (methane) seeping out of the earth there. After some thought, I decided this theme was just dumb. Strike one.

I spent some time considering Easter- and equinox-related myths, as a tribute to the time of discovery. I was quite excited to learn about the pagan Eostre (or Oestre, or Oster, or many other spellings) after whom Easter is named, until I later realized that this mythology is perhaps itself mythological and, more important, that an asteroid had already been named after this G.o.ddess hundreds of years ago. Strike two.

Finally, in mythological desperation, I considered rabbit G.o.ds, of which there are many. Native American lore is full of hares, but they usually have names such as Hare or, better, Big Rabbit. I considered Manabozho, an Algonquin rabbit trickster G.o.d, but I must admit, perhaps superficially, that the "bozo" part at the end was a turnoff. There are many other names of rabbit G.o.ds, but the names just didn't speak to me. Strike three.

These initial attempts had all happened long ago, and I had given up, figuring I would wait for the IAU decision on Santa. But now, with some prodding, I got back to work.

Suddenly, it dawned on me: There was a potentially interesting small island in the South Pacific that I hadn't looked into before. I wasn't familiar with the mythology of the island, so I had to look it up, and I found Makemake (p.r.o.nounced Hawaiian style as "mah-kay mah-kay"), the chief G.o.d, the creator of humanity, and the G.o.d of fertility. I had discovered Easterbunny during the time that Diane was pregnant with Lilah. Easterbunny was the last of these discoveries. I have the distinct memory of feeling a fertile abundance pouring out of the entire universe during that time. Easterbunny was part of that. Easterbunny would be Makemake, the fertility G.o.d of the island of Rapa Nui.

Rapa Nui was first visited by Europeans on Easter Sunday, 1722, precisely 283 years before the discovery of the Kuiper belt object now known as Makemake. Because of this first visit, the island is known in Spanish (it is a territory of Chile) as Isla de Pascua, but around here, it is far better known by its English name of Easter Island.

The name Makemake was accepted quite quickly and with a modest fanfare by the IAU; as predicted, a decision on Santa was soon rendered, only two years after the initial proposals had been submitted. This time there was no fanfare, no press release, no official p.r.o.nouncements. The name just appeared on the official IAU list of names one day as Haumea. Three years after the Spanish astronomers either did or did not fraudulently steal our discovery, we were officially vindicated by the IAU, which accepted our name, signaling that we appropriately deserved the credit.

Sort of.

On the IAU's list, next to the newly added name Haumea, in the s.p.a.ce reserved for the name of the discoverers, is a big blank spot. Haumea, unique among all objects in the outer solar system, has no discoverer. It simply exists.

Oddly, though, for an object that no one discovered, it does have place place of discovery listed. While the name of the object is Hawaiian, based on a proposal by astronomers from California, Haumea was officially discovered at a small telescope in Spain. By n.o.body. of discovery listed. While the name of the object is Hawaiian, based on a proposal by astronomers from California, Haumea was officially discovered at a small telescope in Spain. By n.o.body.

What does any of this mean, officially? Mostly, I think, that the IAU didn't try too hard to figure anything out. Probably the majority of whatever committee was voting thought my version of the story was the most plausible, but there were enough dissenters that a decision was made to soften the p.r.o.nouncement by listing no discoverer and by backhandedly acknowledging the Spanish claim.

I am disappointed that they made no real effort to figure out what happened, at least as far as I can tell. No one ever asked me anything or requested extra information from me. I suspect the same is true of the Spanish side. In the end, this is as good as it will get. I will never know for sure what actually took place in those two days before the Spanish astronomers announced their discovery.

I still haven't drunk the celebratory champagne. The friend with whom I made the five-year bet on the foggy night at Palomar Observatory had generously given me a five-day extension, and Eris fit all of the characteristics that she and I had decided a planet must meet. She happily delivered the champagne the next time she was in town. In the end, though, Eris was not the tenth planet; it was instead the killer of the ninth. Champagne doesn't make a good funeral drink.

Those five champagne bottles sit on my shelf still. I look at them every once in a while and wonder if the time will ever come to pop the corks. I'm still looking for planets, but the bar is now much higher. Anything new that wants to be called a planet needs to be a significant presence in our solar system, and I am not certain that there are any more hiding in the sky. But I keep going. Someday, I hope, I'll be sitting in my office looking at pictures of the sky from the night before, and there on the screen will be something farther away than I've ever seen before, something big, maybe the size of Mars, maybe the size of the earth-something significant. And I'll know. And, as I did years earlier, I'll immediately pick up the phone and call Diane. "Guess what?" I'll say. "I just found the ninth planet." And-once again-the solar system will never be the same.

Epilogue.

JUPITER MOVES.

It takes some time for a kid to figure out that her parents have a separate existence that takes place when she's not around. By the time she was about three, whenever I was gone for a few days Lilah began getting immensely curious about where I was. That place would become a fabled land that she invoked when playing with stuffed animals or making up stories. Taiwan, to which I went one week during her third year and which she can now pick out on any globe, remains perhaps her favorite spot in the world. At one point during her third summer, she had named all of the corners of the swimming pool after different places, and she would cling to my back and direct me where to go next.

"Daddy, I want to go to Chicago."

Swim, swim, swim.

"Daddy, Daddy, Berlin!"

Stroke, stroke, stroke.

"Boston."

Glide, glide, glide.

"Daddy, Daddy, I want to go all the way to Taiwan!"

Taiwan, which she knew to be an island, required momentarily going underwater before emerging on the other side of the Pacific Ocean.

"Now back to Pasadena, California!" which was code for "Let's get out and see if Mommy will bring out some snacks."

Eventually she started figuring out why I would periodically disappear.

"Are you going to go talk about planets?"

And the answer, invariably, was yes.

Lilah loves planets. Other than the occasional dwarf-dog joke, I have never particularly pushed planets on her, at least not any harder than I push them on everyone else. Yes, I point out planets in the sky to her every time we go outside at night, but I do that to everyone. Beginning in that summer of her third birthday, Lilah had been particularly mesmerized by Jupiter. Every night for a few months, it was high in the evening sky-one of the first things to pop out of the murky twilight and reveal itself night after night. Back in the summer, she made sure we went outside right at her bedtime, when it was just barely dark enough to make out Jupiter, so she could say good night to it. As the summer changed to fall and then winter, it would already be dark as we were driving home, and for her, the highlight of the drive was always the moment after we'd climbed the little hill to our neighborhood and we had taken the final left-hand turn to point west; Jupiter suddenly would appear in her window, high enough in the sky to be seen even from the depths of her child car seat.

By late fall, though, Jupiter was no longer the king of the evening skies. Venus had crept up into the twilight to start to steal the show from Jupiter. Or at least, in Lilah's view, to share the show. She went from having only one planet to now having two planets to say good night to every night.

Lilah sees planets everywhere. You never quite realize-until you have an obsessed three-year-old-how prevalent images of planets are in everyday life. She's got them on her lunch box (a gift from friends of mine, of course); she sees pictures in magazines and catalogs; she sees mobiles and puzzles at stores. I would tend to just walk by them without noticing, but she always runs up-"Daddy, Daddy, look look!" She always quickly picks out Jupiter (the big one) and, of course, Saturn, with the rings. She recognizes the blue-and-green look of Earth. And she gets Venus right more often than I think any three-year-old should.

One night, after a long cloudy spell when we couldn't see the planets at night, Lilah looked up at the sky, startled. "Daddy, Daddy, look look! Jupiter moved moved!" And she was right. Venus and Jupiter had been slowly edging closer to each other over the past few weeks, but you wouldn't have noticed it unless you were watching closely. Now they were suddenly so close that even a three-year-old could see that something had changed.

Lilah's pointing out to me that Jupiter moved was-for me-the pinnacle of planetary charm. While most kids and adults can name the planets and point out pictures, almost n.o.body notices the real things, even when they are blazing in the evening sky. Planets are not just things that s.p.a.cecraft visit and beam back pictures from. They're not just abstractions to put on lunch boxes. They are really there, night after night after night, doing what planets do: moving; wandering.

A few nights later, the show got even better. A tiny sliver of a moon appeared low in the early-evening sky and began working its way toward Jupiter and Venus. Lilah and I are moon watchers. And we both know that after appearing as a tiny sliver at sunset, the moon gets bigger and moves east night after night in the evening sky. Based on how far the moon was from Venus and Jupiter, it was clear that in just two nights the moon would be packed tight right next to Jupiter and Venus. It would be a spectacular sight, with the three brightest objects ever visible in the night sky in an unmistakable grouping in the southwest just after sunset.

The night of the triple conjunction, I was on a long flight across the country. As I was packing my bags that morning, Lilah had sadly asked, "Daddy, are you going away to go talk about planets?"

I was. But I didn't want talking about planets to make me miss seeing planets. I knew I was touching down at night in Florida long after Jupiter and Venus and the moon would have set, but I was careful to pick a window seat on the south side of the airplane so I could watch the show from the air. And the sight of the moon and Jupiter and Venus shining in a tight triangle over and behind the wing was as spectacular as Lilah and I knew that it would be. Though it was night in Florida, it would still be a beautiful late twilight in California. I quickly called home and told Lilah all about the view from 30,000 feet and told her to go outside right now and-look! She would see all of our favorite planets.

The tight-packed group of lights low in the early evening sky was the sort of sight that makes even nonnight sky watchers suddenly look up and wonder. A few people would even think to look the next night, I suspected, to see if the sight was still there. They would notice that the moon had already moved farther east and gotten a little bigger, and they would see that the two other bright lights-Jupiter and Venus-were in slightly different spots than just one night earlier. Maybe then a person or two would be hooked. Maybe they would follow the moon's movement for the next week as it grew to full, watching as Jupiter appeared lower night after night, eventually leaving Venus alone in the sky. It would be a show worth following. I knew Lilah and I would watch it. Even when we were continents apart, we'd always be looking for the things that moved in the sky.

ACKNOWLEDGMENTS.

This book would never have been possible without the contributions of many people involved in the research and events described here. I would like to especially thank Jean Mueller and Kevin Rykoski for their early encouragement of and help with the search for large objects in the outer solar system, and Chad Trujillo and David Rabinowitz for many years of hard work and foresight into what might be out there and how to find it. Brian Marsden was always a voice of wisdom and kindness in the otherwise arcane world of solar system politics. My students throughout this period, Antonin Bouchez, Adam Burga.s.ser, Lindsey Malcolm, Kris Bark.u.me, Emily Schaller, Darin Ragozzine, and Meg Schwamb-now Drs. Bouchez, Burga.s.ser, Malcolm, Bark.u.me, Schaller, Ragozzine, and Schwamb-all provided fresh eyes and minds that aided many of the scientific insights described here.

While the research and discoveries were key, the book itself might not have ever been begun without encouragement from Heather Schroder on an early abortive version, and then a jump start from my agents, Caroline Greeven and Marc Gerard, who finally set me to work. Cindy Spiegel took the initial ma.n.u.script and found a way to make small changes with big impacts and graciously laughed at me when I told her I was nervous to meet real real writers. Brad Abernethy provided wonderful editorial advice and encouragement on an early draft, and explained to me that words mean what we think they mean when you say them. Emily Schaller, though mentioned above in her doctoral capacity, also deserves my deepest grat.i.tude for reading every version of every chapter and always providing exactly the right combination of advice, criticism, and encouragement. writers. Brad Abernethy provided wonderful editorial advice and encouragement on an early draft, and explained to me that words mean what we think they mean when you say them. Emily Schaller, though mentioned above in her doctoral capacity, also deserves my deepest grat.i.tude for reading every version of every chapter and always providing exactly the right combination of advice, criticism, and encouragement.

I regret that my father, Tom Brown, didn't live to see most of the time period written about here, but he was nonetheless instrumental in instilling in me my love for s.p.a.ce, science, and living on boats. My mother, Barbara Staggs, has always been my biggest fan, no matter what the arena, and my stepfather, Willie Staggs, my brother, Andy Brown, and my sister, Cammy Thornton, have always kindly tolerated this fact and provided balance, for which I am grateful.

Finally, I have to thank Diane and Lilah, who are the reason for the book and also the ones who allowed it to happen, by letting me mentally slip away on nights and on weekends to write the stories of us, and who continuously allow those stories to go on.

ABOUT THE AUTHOR.

MIKE B BROWN is the Richard and Barbara Rosenberg Professor of Planetary Astronomy at the California Inst.i.tute of Technology, where he teaches cla.s.ses from introductory geology to the formation of the solar system. He is a native of Huntsville, Alabama, where he grew up listening to the tests of the Saturn rockets preparing to go to the moon, and he received his undergraduate degree in physics from Princeton University and his Ph.D. in astronomy from the University of California, Berkeley. He and his research group spend their time searching for and studying the most distant objects in the solar system and drinking coffee. is the Richard and Barbara Rosenberg Professor of Planetary Astronomy at the California Inst.i.tute of Technology, where he teaches cla.s.ses from introductory geology to the formation of the solar system. He is a native of Huntsville, Alabama, where he grew up listening to the tests of the Saturn rockets preparing to go to the moon, and he received his undergraduate degree in physics from Princeton University and his Ph.D. in astronomy from the University of California, Berkeley. He and his research group spend their time searching for and studying the most distant objects in the solar system and drinking coffee.