How I Killed Pluto and Why It Had It Coming

by Mike Brown

  Scientifically, I agreed much more strongly with our second press release, explaining why there were only eight planets. Eight planets made sense if you were a scientific historian and realized that 150 years ago people had already decided to divide the solar system’s objects into big planets and small asteroids and that Pluto—and now Xena, too—thoroughly fit into the category of the small objects. I liked to think of this one as what people would mean when they said the word planet if they really understood the solar system. We hailed the bravery of astronomers for taking a scientifically sound stance in the face of what would certainly be considerable opposition. Even though scientifically I agreed much more strongly with this press release, I was glad we wrote it quickly; it seemed quite clear to me that astronomers would never have the audacity to actually get rid of everyone’s favorite runt planet. Still, to be safe, I thought it best that we have a press release ready. Having the discoverer of the onetime tenth planet agree that it should not be a planet seemed like a powerful line of argument.

  Our third press release was for the possibility that the IAU’s decision would be to simply keep nine planets. Keeping Pluto in the planet club but refusing to allow in bigger newcomers didn’t make sense at all. Yet it did seem like an option that might be on the table, since I had heard a few people say, “Why do we need to change anything when we have nine perfectly good planets?” Our press release said that nine planets was a pretty dumb decision.

  The last press release considered a more extreme possibility: that the IAU would stretch the definition of the word planet so far that there would suddenly be two hundred planets. A small but extremely vocal group of astronomers had been pushing for a while to thoroughly transform the meaning of the word planet. Unlike the ten-planet approach, which was an attempt to understand what people meant when they said the word planet, or the eight-planet approach, which was an attempt to discern what people would mean if they had all of their facts straight, or even the nine-planet approach, which was to stick to literally what people meant when they said the word planet (the nine planets and nothing else!), the two-hundred-planet approach was an attempt to legislate an entirely new and never before anticipated meaning for the word planet. The word was to mean, essentially, “anything in orbit around the sun that is big enough to be round.”

  Why round? It is not simply that astronomers are enamored of that particular shape (though, really, why wouldn’t they be?). It is that that particular shape tells us something. If you throw a boulder into space, it will retain whatever irregular shape it originally had. If you throw a hundred boulders into space together, they might stick to one another due to the tiny amount of gravitational pull that each boulder generates, but they could still have almost any shape you might imagine. But if you put enough boulders up into space together, a fantastic thing will happen: The cumulative gravitational pull of all those boulders will take over. The boulders will pull together and crush and smash one another until you can no longer discern what shapes they had to begin with; instead, they will form a beautiful, simple sphere. Finding something spherical in space indicates that you have found a place where gravity has taken over. I am pretty certain that at no time in the previous several-thousand-year history of the word planet did anybody say “planet” and really mean “things that are round due to self-gravity.” It was a new definition by simple fiat. And it would lead to something like two hundred new planets, most of them out in the Kuiper belt.

  I explained all of this to the person writing the press releases.

  “Why bother writing this one up? It sounds crazy. No one would decide this, would they?”

  Well, yes. I actually thought this was the most likely decision that the International Astronomical Union would make—if it was ever going to make a decision at all.

  “But why would astronomers do such a crazy thing?” he wanted to know.

  Desperation was all I could answer. Desperation.

  As radical as the new definition was, it was the only one on the table that both smelled scientific and also retained Pluto as a planet. I could imagine that it would be hard for a scientific committee to conclude that the definition didn’t need to have a strong scientific basis (the nine- or ten-planet approach). I could imagine that an astronomical committee would be loath to provoke what would certainly be a huge public outcry if it kicked out Pluto (the eight-planet approach). So although the two-hundred-planet approach was the most radical, it had the cover of appearing the most conservative. I could just see it passing.

  I didn’t like the definition, but I could live with it. The good news, for me, was that if this new definition was announced, I would have discovered more planets than anyone else in human history. Not just Xena, Easterbunny, Santa, Sedna, and Quaoar, but dozens more. The bad news was that I couldn’t remember most of their names.

  • • •

  The first anniversary of the discovery of Xena came and went with no hint of what was happening at the IAU. But it was okay. I was busy. Chad and David and I, now joined by some of my students and outside colleagues, wrote scientific papers about the size of Xena, the discovery of Gabrielle (the moon of Xena), the discovery of a thoroughly unexpected second moon of Santa, and the slab of frozen methane covering the surface of Easterbunny; and we still had much, much more to do. There were press releases to develop, talks to give around the country, interviews on TV and radio. But when I think of this time period, I have a hard time remembering almost any of it. What I really remember is Lilah and the moon.

  As with any overeducated first-time parents, we were fascinated with understanding Lilah and what she was thinking and doing and understanding. I began reading scientific books on early childhood development, not as a way of pushing Lilah along faster or making sure she was okay, but simply because it was, at the time, the single most fascinating thing I could imagine. I read studies of the development of facial recognition and motor skill control, but what I found the most interesting of all were studies of language development. It seemed so hard for me to imagine that this little baby, being carried around in a bundle in my arms, would someday be sitting in a chair next to me having a conversation.

  Diane and I often joke about parents who think that everything their children do is exceptional. Intellectually, we always understood that Lilah would likely be good at some things, not as good at other things. Exceptional is a pretty high bar. But reading these books about early childhood and watching Lilah develop, I finally understood. She is exceptional, because early childhood development is about the most exceptional thing that takes place in the universe. Stars, planets, galaxies, quasars are all incredible and fascinating things, with behaviors and properties that we will be uncovering for years and years, but none of them is as thoroughly astounding as the development of thought, the development of language. Who would not believe that their child is exceptional? All children are, compared to the remainder of the silent universe around them.

  Emily Schaller, my Ph.D. student, who was always willing to try to engage my obsessions, handed me a book one day on how to teach your baby a primitive type of sign language. The thought was that children are ready to communicate before they have the vocal motor skills for speech. But they can use their hands and arms and fingers to tell you about the world around them.

  Lilah’s first sign was, not surprisingly, cat (rake two fingers across your face as if to draw whiskers). The two cats—originally Diane’s, now a joint venture—who lived with us barely tolerated the loud newcomer to the house. But they eventually got used to her and realized that she posed no harm, so they would lie close to take advantage of me or Diane being immobilized while holding a sleepy baby and having a free hand available for an ear scratch. Then Lilah learned to roll over. The cats scattered, to eventually return when they realized she was still mostly immobile. Then Lilah started to crawl, and that started the years of Lilah chasing after the cats, the cats slinking away, always out of reach. To Lilah, the cats must have been like the end of
the rainbow: always in sight, always just out of reach, and gone when you get there. Her first efforts to communicate with the external world were targeted directly at them. They, sadly, never returned the favor.

  After cat, Lilah next learned flower. Flowers (scrunch up nose as if sniffing) were everywhere, first only outside on plants, but soon she generalized to flowers on her clothes or her shoes, or in pictures in books and magazines. I wanted to hook up wires and do experiments and comparisons and studies to understand it all.

  “You want to do what?” Diane would say.

  But, really, who wouldn’t? In our own house the most extraordinary thing in the universe was taking place, and it was passing by unexamined, unstudied.

  “There will be no Lilah experiments,” Diane declared.

  I know, I know. I wouldn’t really do it. I didn’t really want to hook up those wires. Mostly I just wanted to hold Lilah tight as she made signs to the world around her, and I wanted to tell her: You are the most extraordinary thing in the universe.

  We had recently bought a new house. For the first few years of our marriage and the first six months of Lilah’s life, we had lived in a diminutive Spanish-style bungalow in a typically densely packed part of suburban Pasadena that I had bought years earlier. I loved my little bungalow. It was the house where I first cooked dinner for Diane. When Diane had moved in, I had warned her: I love this place and never want to move.

  But the house had almost no sky.

  I biked home at night through lit streets, car headlights glaring everywhere. I thought back to the days of living in the cabin and walking the trail by the light of the moon or stars; I thought back even earlier to the days of living on a tiny sailboat in the San Francisco Bay and staring up at the whole sky before finally closing the hatch for the night. From my bungalow, I could sit in the hot tub in the backyard and look up and see slivers of sky. Sometimes I could see the Big Dipper, sometimes Cassiopeia. But in my tiny night-sky universe, I never once saw a planet.

  When Diane suggested that we probably needed to move to a bigger house to fit our now-expanded family, I reluctantly agreed. Maybe it was time. I grudgingly went to look at a few places with her. Nothing felt as perfect as our happy little bungalow. Then one day, with no expectations, we stumbled onto a house perched on top of a massive one-hundred-thousand-year-old landslide. Almost nobody knew it was a landslide, but I had made my geology students write about it nearly a year earlier. How could I not have fallen in love with the house? We bought it three days later and moved in the following month.

  Living on a landslide has its advantages. We have a steep canyon in our backyard, because canyons are easily formed in rubble. We have landscaping boulders of every conceivable size and composition, and if we ever have the need for more, we just dig a foot underground to see what else the landslide brought down. The landslide makes a minor wildlife corridor, so we have an abundance of birds, an occasional bobcat, and even once a black bear.

  For me, though, the best benefit of perching on the tip of the tongue of a landslide with the mountains rising to the north of you is that you have an uninterrupted view to the south. And if you go outside at night and look to the south, you get to see the spectacular constellations. You get to see Orion and Taurus and Scorpius. You get to see the blue of Sirius, the red of Betelgeuse. And best of all, you get to see the planets.

  Lilah and I have spent the years since we’ve moved to our new house tracking Jupiter and Saturn across the sky, watching Venus set into the Pacific Ocean, seeing how red Mars looks in comparison to the pale stars. But more than anything else, we’ve watched the moon.

  When we first moved into the new house, Lilah was still learning new word signs. One of her favorite combinations translated something like this: There is a light; turn it on (hand held overhead, first balled momentarily, fingers suddenly flying open to show you what to do). If you complied, she would even say “thank you” (finger tapping heart).

  One spring night, the nine-month-old Lilah and I sat outside wrapped in blankets staring up at the moon, which was nearing full. A rollicking storm had been through for the past few days, revealing to us all of the places where our new house flooded. But the rain had stopped, and between the thick black clouds covering about half the sky we could see the brightest stars and the bright full moon, which had found itself in a large hole in the clouds and was shining down on the still wet and now sparkling nighttime landscape. I told Lilah about night and the moon and the rain. We heard coyotes across the canyon, and I told her about them, too (and about why the kitties were now going to be solely indoor kitties).

  And then the moon ducked behind one of the thick clouds, and everything got dark.

  Lilah looked around, looked up to where the moon used to be, and looked at me. Then she held her fist up in the air and flung her fingers open. She looked at me expectantly.

  The cloud passed. The moon came back out and once again brightened the landscape.

  Lilah smiled at me and tapped her heart.

  • • •

  I have an extremely vivid memory of the day that summer, a few weeks before her first birthday, when Lilah really learned to walk. She had previously taken a few halting steps before tumbling, or she had scooted along while holding a wall, but one day she instantly went from easily manageable (she would not have gone too far if I had looked away for sixty seconds) to fast, unpredictable, and apt to disappear in seconds. A day earlier, while trying to throw a friend in the swimming pool, I had broken my ankle, and I was now in a cast and on crutches. The fact that I had to take a few steps from the kitchen counter to the refrigerator was something I now mourned. But the worst thing was that Lilah was suddenly up and running just as I was slow on my crutches. The only way I could keep up was to crawl. So, that day, Lilah and I traded. She now walked. I now crawled. I had many theories about the precise symbolism of that transition, and all of the theories were ominous.

  Lilah made up a sign-language symbol for me walking on crutches (two hands held in front of her, pointer fingers moving up and down), which I count as the moment when she first learned to mock me. I was, perhaps unsurprisingly, enamored of the mocking.

  Six days later, still on crutches, I headed to Italy to give a talk at an international conference on the Kuiper belt. We talked about the formation of the Kuiper belt, the surfaces and atmospheres of the objects there, and what they might be made of, but the question of what to call them never came up. But at night, when we went to little cafés (the closest of which was precisely 1,032 crutch-steps away, which felt to me like the distance from Earth to Sedna) to drink prosecco and watch the World Cup soccer games, everyone wanted to speculate about Pluto and Xena and planets. I tried out my arguments about ten planets and about continents. The scientists balked. They didn’t like the idea that the definition of planet would include no science.

  “So you think everything round should be a planet? You think that there should be two hundred planets?” I asked, assuming that that was going to be the obvious response.

  “Of course not!” they responded. Wasn’t it obvious that there were only eight planets?

  I thought the other astronomers were being naïve. It’s easy to sit inside the scientific bubble and make pronouncements, but they were forgetting how much of an impact this decision was going to have on the outside world. No one was going to let Pluto be killed, were they? But still, it was interesting. Within the field of people who studied the Kuiper belt for a living—people who had devoted their careers to the outer solar system and its many, many denizens—it was almost not worth having the conversation. Of course Xena was not a planet. And Pluto likewise. Hadn’t we settled that question 150 years ago when the asteroids became asteroids?

  Naïve, I thought. I remembered back to the days when I used to think the exact same thing. Wouldn’t it be nice to just think about science and not worry about its impact on culture? Wouldn’t it be nice to be able to just say the thing that makes the most sense?


  A week after I got home, my phone rang, and out of the blue I was told by a member of a previously unknown IAU committee (the third planet committee? The fifth committee? I couldn’t keep track) that Xena was to be a planet.

  He couldn’t reveal the details of the decision on the definition of the word planet, but he wanted to prepare me for the onslaught of publicity that would surely follow. As I was the only living discoverer of a planet, he thought it best that I stay humble.

  Humble? I thought, and chuckled to myself. My one-year-old daughter had recently learned to mock me in a sign language she had made up herself.

  While he had not meant to reveal details to me, he already had. The “only living discoverer” could mean only one thing. If the IAU was going to pick the two-hundred-planet definition, there would have been perhaps a dozen living planet discoverers. If there was only one, it was clear that the IAU had decided on the ten-planet definition that I had come to terms with myself. Xena was to top off an elite list.

  “Do you think the rest of the astronomers will go along with this?” I asked.

  I was quickly assured that they would. “I’ve had a lot of conversations in the past few days. This is going to sail through the vote process.”

  • • •

  I went home that night and told Diane. We opened a bottle of champagne and drank to the amazing fact that I had discovered a planet. A planet. I had discovered a planet! After all of this time, Xena was officially going to be a planet, and I was officially going to be the only person alive who had found a planet.

  Just then, Lilah walked around the corner from where she had been playing, saw the crutches under my arms, and immediately stuck out her hands and waggled her pointer fingers.

  Okay, so I was slow, and I still had to crawl to be as fast as my one-year-old daughter. But I had found a planet. No one could take that away from me.