AS AN ASTRONOMER, I have long had a professional aversion to waking up before dawn, preferring 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 sneaking out the door, trying not to wake my wife, Diane, or our 1-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.

It was the last day of the International Astronomical Union meeting in Prague, Czech Republic, and the final item on the IAU agenda 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 half a world away; whatever happened would be big news around the globe.

For me the vote had less to do with the ninth planet than with the 10th. I cared a lot about that 10th planet, because 18 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 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 10th planet. Or maybe, after the vote in Prague, not the 10th planet. Xena had precipitated a year of intense arguments about Pluto, because Xena was Pluto-like in every way—yet larger. It was clear that Xena would share whatever fate was dealt to Pluto. If Pluto was to be a planet, then so too was 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 produced perhaps the most contentious gathering in modern astronomical history. Usually the 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 celestial gossip. On the final day of each meeting, in a session attended by almost no one, resolutions are passed, usually all but unanimously. This year was different. The usually placid astronomers had spent their time in Prague bickering day and night about Pluto and the definition of “planet.” While several typically unintelligible resolutions were indeed to be voted on, 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. Then, after three mostly esoteric and tedious hours, it would all be over.

IN GREEK AND Roman times, there were seven planets: Mercury, Venus, Mars, Jupiter, and Saturn, and also the sun and the moon. Earth was not considered a planet, since it was the center of the universe. Not long after people realized that the Sun, rather than Earth, was at the center of the solar system, new planets started showing up in the sky. Uranus was discovered in 1781, and Neptune in 1846. Astronomers were looking for the next new planet past Neptune when they stumbled on to Pluto in 1930. Assuming it was massive and alone at the edge of the solar system, they called it a planet. We know better now. Pluto is tiny, and one of many thousands of things in orbit out past Neptune. The eight major bodies of the solar system dominate their regions of space and push anything nearby into wildly elongated and tilted orbits. Pluto and all of the other objects out there buzz about like flies swarming between the stately giants. Calling Pluto a planet on par with the other eight was a mistake in 1930. It was time to rectify that mistake now.

Yet it was eminently possible that, in a desperate attempt to rescue Pluto’s planethood, the Prague conference would conclude that Xena, too, was a planet. This prospect was scientifically suspect, but emotionally alluring. I admired this little point of light moving through the sky that almost no one other than I had even seen. At any point, day or night, winter or summer, if you walked up to me unannounced and said, “Quick! Where is Xena?” I could point an outstretched finger to somewhere in space and locate it, with an error of about a hand’s width. If you asked me, “How big is Xena?” I would point at the moon and say, “Imagine a frosty world about half that size.” If you asked me what it would be like to walk on the surface of Xena, I would ask you to imagine walking on a frozen lake in the dark of the new moon. That was Xena. My tiny, frozen, nearly invisibly lovely planet. Or not.

Other than my wife, Diane, who had been the first person I called when I spotted Xena, few shared my attachment to it. But Pluto was another matter. Generations of schoolchildren had grown up with Pluto as a certified, even rather chummy, planet. It provided the “pizzas” in the mnemonic that has helped millions to remember the order of the planets orbiting our sun: My Very Educated Mother Just Served Us Nine Pizzas. The word coming out of Prague was that in deference to both tradition and sentiment, a secret committee setting the conference agenda was working to retain Pluto’s planetary status by slyly redefining what a planet is.

As someone who spends much of my life trying to be not just a scientist but also 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 was not a comfort.

I had spent hours talking to the press about the solar system and the planets, and why the proposed redefinition was fatally flawed, and explaining why Pluto—and Xena—should really not be considered planets. At first reporters were shocked. They were calling to get quotes from the newly minted planet discoverer about how fabulous all of this was. Instead I was telling them that everything they had heard from the IAU made no sense. Suddenly there was controversy.

HOURS BEFORE DAWN in California, the astronomers in Prague had awakened to read the final wording of the resolutions to be voted upon. And the wording mattered. Cosmic distrust in Prague was running so high at this point that many assumed that the clearly pro-Pluto committee would attempt to subvert the anti-Pluto astronomers by sneaking in wording that would keep Pluto a planet no matter what the vote.

In a press briefing room at Caltech, I projected onto a large screen a just-posted copy of the precise wording of the resolutions. I scrolled through resolutions on “precession theory and definition of the ecliptic” and similarly boring fare until I reached Resolution 5A: Definition of “planet.”

The resolution was confusingly worded, but it seemed to reach the correct conclusion. In a footnote it clearly stated: “The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.” Well, then. They were going to kill Pluto after all, taking out Xena as collateral damage.

“But what about Resolution 5B?” someone asked me.

Resolution 5B: Definition of a classical planet.

Huh? “Classical” planet?

Resolution 5B simply changed the word “planet” in the previous resolution to “classical planet.” According to Resolution 5B, there would now be eight classical planets and four newly defined “dwarf planets.” Classical and dwarf simply became different but equal subsets of the overall category of planets. It was the Pluto escape clause! The committee was trying to sneak Pluto back in! In fact, both Pluto and Xena would become planets under 5B, and probably several main-belt asteroids and several Kuiper Belt objects would join them as well.

Though vehemently opposed to such trickery, I was in California, not Prague. I had been told that many of the astronomers in Prague were prepared to go along sheepishly with such a proposal, rather than fight it. All I could do was hold my breath and hope that the astronomers were paying attention and would revolt. As the resolutions were voted on, astronomers in favor of 5B held up yellow cards to signal their support. There were many. The counting took a few minutes.

“Mr. President, we report 91 votes in favor.” That didn’t seem like enough, but I couldn’t tell from the tiny Web video we were watching precisely how many astronomers were present in Prague.

“All opposed to the resolution?” Astronomers opposed to 5B, who wanted to firmly cap the solar system at eight planets, held up their cards. A sea of yellow filled the auditorium, which immediately erupted in applause. “I think, Mr. President, a further count is not honestly needed.” Resolution 5B had not passed.

“Pluto,” I said, “is dead.”

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

The remainder of the day was a blur of interviews, condolences (after all, I had lost my claim to a planet), and congratulations. That afternoon I made my way to a radio station for a call-in program. When we went live on air, I suddenly realized that the other guest on the program was a member of the once-secret planet-definition committee, live from Prague! He seemed tired, and he definitely didn’t seem happy. He talked about how he thought the vote had done a disservice to astronomy. I said I thought astronomy, in standing up for science, had done a great service to the world.

He said that he was sad that no one would ever again discover a new solar-system planet under the current definition.

“You know,” I said, “when you tell me that no one will ever discover a planet again, I just take that as a challenge.”

Over the course of the radio show, we both answered questions from callers. It was becoming clear that the idea that Pluto was no longer a planet was not going to be an easy sell. Throughout the hour, the host collected suggestions for a new mnemonic for remembering the order of the planets minus Pluto. Some offered a slight modification of My Very Educated Mother Just Served Us Nine Pizzas—turning “Nine Pizzas” into “Nachos” or into “Nothing,” which was a bit funnier. But the best mnemonic, and the one that I still tell people to use to this day, was sent in by an anonymous listener and sums up the feelings that would envelop much of the world over the next days, weeks, and months: Mean Very Evil Men Just Shortened Up Nature.

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.