How I Killed Pluto and Why It Had It Coming - Mike Brown (2010)


Living on the outskirts of Los Angeles with a clean sweep of the sky to the south of us, we have a very nice view of the standard flight path for arrivals and departures at LAX. Those things moving through the daytime sky that turned into lights brighter even than the stars at night held a special fascination for Lilah. Her sign-language symbol for airplane (arm held aloft with hand parallel to the ground) got much use. First it was just for those little moving dots in the sky, then it was for pictures of airplanes in books, and then, one very exciting day when Lilah was thirteen months old, it was for an airplane that she actually got to fly in. I spent the whole morning trying to prepare her for the mental transition:

“Look! Airplanes in the sky!” I said, as we got close to LAX.

“Look! The airplanes are driving around on the ground!” as we were moving through the airport.

“Look! That is the tunnel people take to get on to the airplane!” as we were at the gate.

“Look! We’re now inside!” as we sat down.

For what I had assumed would be a difficult cognitive leap, Lilah took it all in stride. Of course we’re inside the airplane and now flying in the sky, Daddy. What else would we be doing?

We were taking our first family vacation, two weeks on Orcas Island, the largest of the San Juan Islands, northwest of Seattle. Diane had lived on Orcas Island for her high school years, and her mother still lived there. It was the first place Diane and I had ever gone together on an official vacation (Hawaii together? That was just work). And now we were bringing our daughter there. Diane has an affinity for the annual Library Fair, where used books get sold on a Saturday morning in August at the otherwise sleepy farmers’ market. For reasons that I, as a non–native islander, can never fully understand, the Library Fair is an unspoken homecoming day; previous island inhabitants show up, as if by accident, to stroll around on Saturday morning, peruse the used books, and snack on barbecued oysters.

I love the Library Fair and—out of sheer exuberance—always buy used books that I would not otherwise even glance at. And then I sit on Diane’s mother’s porch on a midsummer twilight lasting until well past ten o’clock and read.

But during this very first family vacation with Lilah, I had no opportunity to relax and read on the porch. My vacation coincided with the once-every-three-years meeting of the International Astronomical Union, this year in Prague. And at this meeting, for the first time in history, they were finally going to vote on the definition of the word planet.

Why wasn’t I there? Why was I vacationing half a world away from where the astronomical action was?

It’s a good question.

There are four answers to that question. First, I love the Library Fair. Second, it was our first family vacation. Third, no one—not even the astronomers who found themselves in Prague—had been warned that the vote about planets was imminent. I admit, had I known ahead of time that this vote was going to take place, I might have felt obligated to be there rather than to abscond to a small island in the Pacific Northwest. Luckily, I didn’t know. Fourth, and probably most important, I am not a member of the International Astronomical Union. I would have been ineligible to vote. I’m embarrassed to admit that I can’t get myself to fill out the paperwork to join. It’s all because of Question 12 on the form. After the form asks for your academic qualifications and awards, both of which I can handle, it then quizzes you about your miscellaneous special distinctions. And then I stop. Well, I think, I’m no William Herschel (the discoverer of Uranus, which is indisputably a planet). I’m no Adams or Leverrier or even Johann Galle. (Adams and Leverrier predicted the existence of Neptune, and Galle confirmed it.) Really, I wonder, do I have any special distinctions? And each time I get to that spot in the application, I have to stop and put down my pen. There was no reason to bother going to the International Astronomical Union meeting in Prague because I would not have been let in the doors.

•   •   •

I was sitting in Diane’s mother’s house on Orcas, watching the sailboats navigating Westsound out the window, when an e-mail arrived from the other side of the world telling me the details of what, precisely, the IAU was going to vote on. I read it to Diane in my excitement.

“Diane, Diane, it says right here that the planets are to include the big eight, of course, and then also Pluto and 2003 UB313—that’s Xena—and wait a second, there are a few more.” I was confused. Xena and Pluto were nine and ten. But there was also to be Ceres—the asteroid discovered in 1801 that was declared not-a-planet sometime around 1850. And in a surprise that I had never anticipated, Charon, the moon of Pluto, which was about half the size of Pluto, was to be number twelve. Twelve planets. Not eight, nine, or ten, or even two hundred, which I would have understood. And Charon? The e-mail didn’t make any sense. I didn’t recall any discussion in which naming Pluto’s moon a planet had ever come up before. What was the committee thinking? Who in their right mind would declare Charon a planet?

I reread the e-mail carefully. The committee, which had met in secret, was adhering to the notion that “all round things are planets,” which I had thought was a bad idea to begin with but which I at least understood and could support as a scientifically rational and consistent definition, even if a poorly chosen one. If the assembled body of astronomers thought that that was the right way to define the word planet, I would be disappointed personally, but I would get over it. After all, I would still get a few planets out of it.

The secret committee had its reasons, which were passionately stated. First: The word planet should have a scientific basis. Who was I to argue against that point? I had been willing to go along with a cultural definition instead of a scientific one, but if the astronomers were going to insist on science, I could hardly say no. And second, they suggested that in deciding whether an object is a planet or not, you should be able to tell just by looking at it—in other words, you shouldn’t have to know anything about where it is and what it is doing and what else is around it. The committee didn’t buy the idea that planets should be the small number of unique important dominant objects in the solar system.

And then they discussed the newly proposed twelfth planet, Charon.

Charon is the biggest of Pluto’s three moons. It was discovered, accidentally, in 1978 by James Christy, an astronomer at the United States Naval Observatory who was examining old photographs of Pluto and noticed a slight bulge coming and going, first on one side and then the other. Though Charon is smaller than our moon, than four of Jupiter’s moons, than one of Saturn’s moons, and than one of Neptune’s moons, making it only the eighth largest moon in the solar system, it is big proportionally to Pluto. And because it is big in proportion to the planet around which it orbits, it alone of all of the moons in the solar system deserved to be a planet.


In the proposal from the committee, Charon was considered to be a planet for two reasons. First, it was big enough to be round, which was in itself a good enough reason to be considered a planet if you’re inclined to think of planets that way. But there are many round objects in the solar system that no one considers a planet. My nemesis the moon, for example. In fact, the proposal from the committee specifically excluded moons from being called planets. But it made a special exception for Charon—smaller than our own moon by a factor of about sixty—for one reason: Pluto and Charon go around a center of mass that is a bit outside Pluto.

Here a bit of quick physics is necessary (and I would like to point out that the fact that we need a physics lesson to explain the proposed definition of the word planet is already a bad sign). Whenever an object orbits another object (the moon about the earth, the earth about the sun, for example), it is not that the bigger object is stationary while the smaller object goes in circles. Instead, both objects go in circles around what is called the center of mass. You can find the center of mass of the earth and moon, for example, by finding a really large seesaw, putting the earth on one end and the moon, which has only 1 percent the mass of the earth, on the other end, and trying to make them balance. In the case of the earth and moon, you would have to move the pivot point to a location about a quarter of the way inside the earth. The seesaw is now balanced, and you have found the center of mass. In the twenty-nine days it takes for the moon to go in its big circle around the earth, the earth, too, in addition to traveling around the sun, goes in a tiny circle that is smaller than the earth itself. Rather than the moon circling the earth, both objects really circle around the point inside the earth that is the common center of mass.

There is nothing particularly special about the location of the center of mass. If you were to find yourself at the precise spot that is the center of mass of the earth-moon system, the only thing unusual that you would notice is that there would be one thousand miles of rock on top of your head.

Pluto is only about twice the size of Charon, so if you put Pluto and Charon on the cosmic seesaw you would find that the balance point is a little bit outside Pluto, rather than inside it. Again, there is nothing particularly special going on there. If you were to find yourself at that precise spot, you would only notice that you were very, very cold and could no longer breathe.

According to the IAU proposal, though, the obscure fact that the center of mass of the Pluto-Charon system sat a bit outside Pluto rather than a bit inside it made all the difference. It suddenly turned Charon into a full-fledged planet, and Pluto-Charon into the solar system’s only double planet. Pluto lovers everywhere would be thrilled. Pluto’s status was about to change from imperiled to wildly distinctive. It would suddenly be the only place in the solar system you could go and get two planets for the price of one.

Except, of course, that the proposed definition was crazy. The members of committee first argued that only the object itself, and nothing else nearby, should be considered in determining whether the object was or was not a planet. Then they changed their minds and argued that satellites, though round, were not planets, because they were in orbit around larger round things instead of the sun. And then they changed their minds again and said that Charon, though small in comparison to other satellites in the solar system, was a planet because the common center of mass of the Pluto-Charon system was outside Pluto rather than inside it, so that, technically, Charon orbits an empty spot in space rather than Pluto. Because it doesn’t orbit a planet, it was therefore not—by this argument—a satellite.

So here is how you tell, in the committee’s opinion, that something in the vicinity of the sun is a planet. Look at it and see if it is round. If it is, then it might be a planet. Next, check to see if it orbits around something else instead of the sun. If it does, then it’s probably just a moon and not a planet. But before you know for sure, calculate the center of mass (if you even know the masses of the bodies in question, which you usually don’t) and see if it is inside or outside the larger body. Then you know. It’s all quite simple.

While the inclusion of Charon was the most jarring aspect of the proposal, there was one other oddity that I couldn’t make sense of. The committee said that all round things were planets (except for moons, which weren’t, except for Charon, which was). I had estimated that about two hundred objects in the solar system would fit that criterion, but the IAU had done its own estimate and come up with its own number: twelve.

Why would Charon and the asteroid Ceres be added, but not the dozen known Kuiper belt objects that were larger than Ceres? And the hundreds that were smaller but almost certainly round? It was as if the International Arboreal Union were to tell you that all things with trunks and bark and branches and leaves were to be called trees, but then it told you that the only trees were oak trees, maple trees, and elm trees. You would be right to ask: How can you make a very precise definition of tree and then claim that things that very precisely fit your definition are not, in fact, trees?

Why would the International Astronomical Union do such a thing? I have a theory that I strongly believe to be true, but which is strongly denied by everyone I’ve talked to who might have more intimate knowledge of how the decisions were made. My theory is that the IAU decided that keeping Pluto as a planet and adding three new planets—Xena, Charon, and Ceres—would seem like a minor change to the order of things. It knew that after the newspapers declared that the solar system now had twelve planets and it proudly exclaimed that its new definition was the first true scientific definition, the pro-Pluto crowds would be satisfied and no one would be terribly startled. Three new planets? Yeah, that happens every century or so. No need to get alarmed. Who could complain? It wouldn’t elicit anything like the reaction people would have to the headline “Solar System to Have 200 Planets!” Given the choice between scientific rigor that might cause protests and a scientific whitewash to conceal reality, the IAU chose the latter. The first scientific definition of the word planet was afraid of its own scientific shadow.

From my increasingly stressful vacation spot on Orcas Island, I got ahold of the committee member with whom I had originally spoken, who was in Prague to present the committee report in the next day or two. I told him I thought the committee recommendation was a mess. How could Charon be a planet? How could it say there were only twelve round things? It made no sense.

He calmly explained the committee’s reasoning and said that he would make sure that in the press release and the press conference it would be very clear that many, many more objects were on the way to being included as planets. And, he mentioned again, he had already talked to many of the astronomers in Prague, and there was nearly universal support for the new definition.

There was clearly nothing I could do. I was on a remote island on the wrong continent; it was impossible for me to have any influence over what was happening in Prague. And in Prague the very next day, they were going to declare that I was one of only seven people in human history who had ever discovered a new planet in the solar system. Who was I to complain?

That night, long after Lilah was asleep and Diane had crawled into bed, I walked (limped, really, but I was now in a walking cast, at least) down to the rocky shore. I could see north across the strait to the islands off the coast of Canada. I could see the deep twilight still casting its final red rays on one of the triangular volcanic peaks over toward the mainland. I turned around to look back at the island, back to the south, but my view of the southern sky was blocked by madrone trees growing close to the water. Farther down the beach, some rocks jutted out into the strait; I’d have a view from there. I hobbled down to the rocks and slowly made my way out to the point. From here I could see the unobstructed southern sky. Low to the south, masquerading as the brightest star around, was Jupiter, undisputed king of the planets.

I sat on the rock and watched the sky and looked at Jupiter. Who was it who first noticed that Jupiter moves? You can sit and stare at it all night long and not tell a thing. You can come back the next night, and unless you’re looking very, very closely, you will still probably not notice anything different. But Jupiter moves. It’s a wanderer. A planet.

I know we’re past the point that when people say the word planet they mean an object that wanders across the sky. In fact, we’re so far past that point that most people never even realize that the planets really are up there wandering night after night. Planets are, to most people these days, pictures from spacecraft, drawings on a lunch box, models in a museum. Meanings can change. After tonight the word planet would change again, adding to the pantheon a little point of light moving through the sky that almost no one other than I had even seen. But it was real enough to me. 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 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 image walking on a frozen lake in the dark of the new moon. That was Xena. My tiny, frozen, nearly invisibly lovely planet. I looked off to the east, where Xena was just about to rise above Mount Constitution, and thought: So be it. I was ready for the next day.

I stared back at Jupiter, wishing I had thought to bring along binoculars so that I could pick out its miniature solar system of icy moons circling it. I tried to pretend I could tell that Jupiter was moving across the sky. The earth rotated. The stars moved toward the west.

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 an 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 e-mail 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.

My phone calls with the press and conspiratorial e-mails with astronomers in Prague continued for most of two weeks, first from Orcas and then from Pasadena, after we returned home from our vacation. Everything was building toward the final afternoon of the final day of the IAU meeting, when the deciding vote on the definition of the word planet would finally be held.

The vote was going to be broadcast live around the world, and I was going to host a packed media event to watch it, even though afternoon in Prague was before dawn in Pasadena. By 5:00 a.m. the news crews and I were setting up in a room usually taken up by press conferences about the latest southern California earthquake. The vote on the resolution that could completely change the way people looked at the solar system was slated to take place in under an hour. That morning, the astronomers in Prague had awakened to read the final wording of the resolution 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 secret committee would attempt to subvert the clearly anti-Pluto-as-a-planet majority by sneaking in wording that would keep Pluto no matter what the vote.

Sitting at a desk in the earthquake room in Pasadena in front of the still assembling press, I projected onto a large screen a just-posted copy of the precise wordings of the resolutions, which I had found at the meeting website. Along with the news crews and, by now, a growing crowd of interested onlookers from the Caltech community, I read, for the first time:

Resolution 1: Precession Theory and Definition of the Ecliptic

I only then realized that there was more on the agenda than Pluto and that this morning might be much longer than anticipated. While I know what precession theory is, and I even knew the definition of the ecliptic, I wasn’t even slightly interested in knowing the precise definition being proposed here—and neither were most, if not all, of the astronomers in Prague.

Resolution 2: Supplement to the IAU 2000 Resolutions on reference systems


Resolution 3: Re-definition of the Barycentric Dynamical Time, TDB

I must have missed the original definition.

Resolution 4: Endorsement of the Washington Charter for Communicating Astronomy with the Public

I began to understand why, until now, no one had ever gone to the voting part of these meetings.

Resolution 5A: Definition of “planet”

Finally! I quickly read through the definition. Though confusingly worded and perhaps poorly thought through (not surprising, given that the final wording had probably been hammered out late in the night), the definition led to reasonable results. It even included a footnote that clearly stated, “The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune,” and that Pluto and Xena, along with the asteroid Ceres, were to be called “dwarf planets,” a term no one had ever heard before. The resolution was clear to point out that dwarf planets are not planets, which I found an odd use of the English language.

The first question from the press: “Dwarf planets are planets, right?”

No, I explained. The resolution was pretty clear. There are eight planets; dwarf planets, of which there might be hundreds, were clearly not planets.

But how could something be called a dwarf planet yet not be a planet? they wanted to know. A blue planet is a planet, right? A giant planet is still a planet. A dwarf tree is still a tree. How can a dwarf planet not be a planet?

Such is the beauty and frustration of definitions, I suppose. But I agreed that it seemed a poor choice, and an odd phrase to make up out of the blue. Something seemed suspicious. Still, the resolution was clear: There were only eight planets. If the astronomers voted yes on Resolution 5A, Pluto was clearly dead.

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

I hadn’t gotten around to reading that one yet. I turned to the screen.

Resolution 5B: Definition of Classical Planet

Huh? “Classical” planet? It was the Pluto escape clause! Resolution 5B simply changed the word planets in the previous resolution to classical planets. There would now be eight classical planets and four dwarf planets. With the quick addition of one word—classical—in front, dwarf and classical simply became different but equal subsets of the overall category of planets. Suddenly, dwarf planets were planets after all. The committee had indeed tried to sneak Pluto back in. The odd phrase dwarf planet had been invented in the previous resolution to allow the possibility that Pluto could rise from the underworld to live again.

Like the previous resolution, this definition was also muddled. Why “classical” planets? Shouldn’t the phrase classical planets refer to those known in the classical world? 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. Uranus, discovered in 1781, and Neptune, discovered in 1846, were a few thousand years postclassical. Calling the largest eight planets “classical” made no sense at all.

I explained to the journalists in the room the now overly complex possibilities of the vote’s outcomes and what the fate of Pluto would be in each case. Finally, the question came: “Do you think Pluto should be a planet?”

I sighed; it would have been thrilling to be considered the discoverer of a planet. “No,” I responded. “Pluto should not be a planet. And neither should Xena. When Pluto was discovered in 1930, there was nothing else good to call it, but by now we know that it is one of many thousands of things in orbit out past Neptune. The vote today would rectify an understandable mistake made in 1930. Going from nine planets to eight planets would be scientific progress.”

By 6:00 a.m. in California it was 3:00 p.m. in Prague, and the assembly was about to start. We were going to eavesdrop on the vote courtesy of a jumpy, low-resolution webcam broadcasting the event. I found the link for the webcast, clicked on it, and projected it onto the oversized screen behind me for everyone to see. It ended up filling an area of about one square foot. If you looked closely, you could see inch-high astronomers filing into the room.

Much of the next hour is a blur in my memory. After we watched an Austrian barbershop quartet there were nine hundred new members to be voted in and the first four resolutions to sit through. It would be a long morning. I muted the sound and opened the floor to questions, of which there were many. I can’t remember a single one. On the tiny video, we could see people making speeches and raising yellow cards to vote on Barycentric Time. Someone finally brought me coffee. The first four resolutions quickly passed, with little discussion and without a single vote of no.

Finally the text for Resolution 5A appeared on the screen; we quickly unmuted the video stream and listened in. The once-secret committee, now beaten down by other astronomers, read and explained the resolution. The floor was opened for comment. One by one astronomers raised their hands and were passed a microphone. Here are some excerpts from the scientific debate of the learned astronomers:

Resolution 5A, Section 2 starts “a dwarf planet.” Could you put dwarf planet in inverted commas, put quotation marks around dwarf planet? It is a definition. It should be in quotation marks.

The press assembled with me chuckled.

At the beginning of 5A we talk about planets and other bodies. That could be taken to include satellites. We didn’t mean it to include satellites but it could be read to mean satellites.

The assembled press looked at me to see if this was significant. I shrugged my shoulders.

I suggest in part 3 of 5A where it says “all other objects” you insert “except satellites” and thank you to the people who suggested those points. I think they are a great improvement.

Chuckles all around.

The order in which we have the resolution printed is not the order in which some countries do business. In some countries you do the amendments first and then vote on the substantive resolution.

More laughs.

“Wait!” I said, quickly turning the volume down. “This comment is really important. This part is insidious. This is deliberate! 5B, which is an amendment to 5A, is voted on after 5A. 5A, which says Pluto is not a planet, will have general support, and then 5B will get snuck in to subvert the intentions of 5A. And no one seems to care.”

But no one other than me seemed to grasp the enormity of the conspiracy at hand. Sure, perhaps I was a bit on the exhausted side at this point and inclined to believe that the secret committee had also conspired to assassinate Abraham Lincoln, Archduke Ferdinand, and Julius Caesar, but just because I was being paranoid didn’t mean I was wrong.

I turned the volume back up, and we were back to punctuation:

The inverted commas look right when you see them, but you don’t speak them. Could you not think of a new word which doesn’t exist in the dictionary so that it doesn’t have any baggage, and instead of calling it “dwarf planet,” use some word, since it’s an entirely new thing.… What you need is a new word rather than combination of old words; but a planet is a planet and so is a dwarf planet from a schoolmaster point of view.

I was feeling punchy and kept interjecting. “Yeah, he is right,” I muttered. “ ‘Dwarf planet’ is a dumb phrase. For years we’ve called things like Pluto and Xena ‘planetoids’—planetlike. That was a perfectly good word yesterday. But they’re trying to be sneaky, they are. ‘Dwarf planet’ is dumb, but they need it so Pluto can become a planet with 5B.”

The press at this point began to think that I was perhaps as crazy as all of the astronomers arguing over punctuation in Prague.

A question from the astronomical floor: “How does Charon fit?”

Right. At this minute there is confusion about Charon. If we pass 5A, Charon is not a planet. Right now I think there is confusion.

Someone else interjected: “It’s a satellite! As long as it remains a satellite, it’s out with this resolution.”

Comment: “A point of clarification for me: Is a dwarf planet considered a planet?”

“That is Resolution 5B.”

“In 5A a dwarf planet is not a planet?”


In perhaps my favorite exchange of the very early morning, the question “Do I understand correctly that we are not anymore entitled to use the word ‘planet’ for planets around other stars?” elicited the response: “Are you referring to floaters, sir, or are you talking about extrasolar planets?”

Floaters? All I could think of were those little spots that you can sometimes see floating in your eye. I never heard the answer because I was at this point just shaking and shaking my head wondering how much longer this could possibly go on.

From a pedant: “Last Friday you mentioned we are not voting on the footnotes, but now you are referring to the footnotes. So are we voting on the footnotes or not?”

Response: “We were at one point trying to say that the footnotes are not part of the resolution. I think that position is not tenable; it is a stupid position. Therefore the footnotes are now part of the resolution.”

Out of nowhere: “There is so much left in the resolution to common sense that I would propose to drop the entire resolution and leave Footnote One.”

That was just about the best comment of the morning. The astronomer was right: The resolution that came up with a definition was so poorly written and vague that it would have been clearer to simply say what Footnote 1 said: The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Everything else was just an attempt to explain why—and a poor attempt at that.

The commenting went on for another hour before, mercifully, someone called for a vote. Those in favor of Resolution 5A, which would create eight planets and an unspecified number of dwarf planets, were asked to hold a yellow voting card in the air. The room was filled with the color of the sun. There was no need to count. Resolution 5A passed with overwhelming support. Pluto was, correctly, no longer to be classified with the other eight planets. It was a moment that I never thought I would see in my lifetime.

The press in Pasadena were aghast and astounded and excited. They were ready to hit the “send” button to upload their stories.

“No no no, wait!” I told them. There was still Resolution 5B! This was where the conspiracy would happen! This was where the secret committee would subvert the will of the astronomical community! “Wait and watch!” I told them.

We watched. And then the most amazing thing happened. In the still-too-early fog of a not-enough-coffee morning in Pasadena, with the press watching astronomers half a world away, awaiting the secret sign to the pro-Pluto brotherhood to emerge to protect the god of the dead, I saw, instead, the moderator of the meeting stand up and make a few simple statements that put everything in precisely the right place. Where were the conspirators? Where were the daggers? Maybe I was in need of sleep.

Here is what she said:

5B involves inserting one word. Surely not a serious matter. However. For the benefit of non-astronomers present [but, really, isn’t she doing this for the astronomers?], I want to do a bit of teaching, which demonstrates that resolutions are non-linear, and small changes have big effects. Excuse me while I dive under the table. [She pulls out a large beach ball, to represent planets, and a stuffed dog—Pluto!—to represent, well, Pluto.]

At the moment, right now, having passed resolution 5A, we have planets, the eight that are named [points to beach ball], we have dwarf planets [points to stuffed Pluto], and we have small astronomical bodies that are non-spherical. If we reject everything else this afternoon that is what will stand. If, however, we add the word “classical” to this group [beach ball], then we have adjective planets [beach ball], different adjective planets [stuffed dog], and it could be argued that what we are doing is creating an umbrella category called planets under which the classical planets and the dwarf planets fit. And if we do this then that [pulls out umbrella, puts beach ball and stuffed Pluto under it; audience erupts into applause] pertains.

“Who is that?” someone in the press asked me.

The speaker was Jocelyn Bell, who was widely considered to have deserved a Nobel Prize in 1974 for her discovery of pulsars. I didn’t need to speak; I just smiled. No conspiracy was going to happen on her watch. Although I wasn’t sure what the outcome would be, astronomers were going to decide based on knowing exactly what they were voting for.

Only two comments were allowed. The first, in favor of the pro-Pluto resolution, was from the member of the once-secret committee who had called and told me that the committee’s original definition, now dead, had been assured of passing. Wearing a tie with planets on it, standing in front of the auditorium, he looked tense, angry, and maybe a little sad. He made his case:

Using the words “classical planets” is a compromise which allows more than one kind of planet in the universe. Yet advocates of the [eight-planet] model have refused this term. They will tell you why. Listen carefully. The word planet is being restricted to just one narrow point of view. Their restriction means that a dwarf planet is not a planet. It would be like saying a dwarf star is not a star. We can fix this. Will we have too many planets? Will we confuse the public? No. The distinction is as simple as an umbrella. Pluto is a planet, but it is in the dwarf planet category. So please pass 5B. The word planet must be shared.

I almost felt bad enough to want to give in. I didn’t object to dwarf planets being considered planets, which was all he was talking about. But I did object to the other planets being termed “classical planets.”

For the anti-Pluto side, a British astronomer stood up and spoke:

The key issue is the definition of the concept planet. This is a very important decision to be taken by the IAU; Resolution 5A is very close to the definition that was agreed by consensus at the meeting on Tuesday. There it was made clear that 3 distinct categories were being defined. Planet, dwarf planet, and small solar system body. The amendment [5B] proposes to insert the word “classical” in front of the word planet. It is inconsistent with the 1st paragraph of Resolution 5A. And it transforms 3 distinct categories into 2, planets and the rest, and that too has been made clear. In answer to the question, how many planets in the solar system? Resolution 5A gives the clear answer: 8. Resolution 5B implies at least 11 and soon several dozen. Both Pluto and Ceres become planets, and probably several main belt asteroids and several Kuiper belt objects as well. Resolution 5B not only removes a fundamental dynamical distinction for a planet, it is confusing and internally inconsistent. In my view it should be rejected.

Sadly, even though I was all in favor of rejecting the resolution, I found almost none of the arguments compelling. Who cared what the consensus was on Tuesday? The final vote was today! And really, if the concepts were significant, wasn’t it more important to make sure to get them right than to worry about the precise wording of the resolution? Besides, would it matter if there were eleven or more planets? It wasn’t the number that mattered, it was getting the concepts right. I realized that I wouldn’t have minded if there were “major planets” and “dwarf planets” instead of “classical planets” and “dwarf planets.” I guess my own version of pickiness was just as bad as anyone else’s.

The vote was called. If the resolution passed, Pluto would be a planet again, and Xena would officially be part of the club. Chad, David, and I would be the only living discoverers of a planet in the world. At least for now. And still I didn’t want it to happen.

“All in favor of the resolution?”

Astronomers in favor of 5B—in favor of repromoting Pluto—held up their yellow cards. There were many. The counting took a few minutes.

“Mister President, we report ninety-one votes in favor.”

That didn’t seem like enough, but I couldn’t tell from the tiny webcast precisely how many astronomers were there in the auditorium.

“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, Mister President, a further count is not honestly needed.”

“Then it’s clear that Resolution 5B is not passed.”

At that point it was final. And I said to the assembled press: “Pluto is dead.”

The cameras whirred; correspondents talked into their microphones; 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.”

Most of the remainder of the day was a blur of interviews, condolences, and congratulations. That afternoon I made my way to the studio of a radio station, where I was scheduled to be on a call-in program broadcast throughout Los Angeles. When I showed up at the studio, they told me that another astronomer would be calling in as a guest.

Great, I thought. Another guest would help me to stay focused and coherent.

When we went live on air, I suddenly realized that the astronomer was none other than the member of the once-secret planet-definition committee, live from Prague! It had been an even longer day for him than it had been for me.

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 had done a great service to the world.

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

“You know,” I said, over the radio to him half a world away, “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. Some gave a slight modification of the previous standard—My Very Educated Mother Just Served Us Nine Pizzas—by 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, sent in by an anonymous listener, 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.