by Mike Brown
Today I know Santa by its official name, chosen by David: Haumea. The mythological Haumea is the Hawaiian goddess of childbirth. Her many children, which compose a large subset of the population of Hawaiian deities, were broken off from different parts of her body. The astronomical Haumea has been equally prolific. In the years since its discovery, we have found many other objects in the outer solar system that we can now trace back to having originally been part of the surface of this object. We think that at one moment early in the history of the solar system, a much larger Haumea was smashed by another icy object in the Kuiper belt traveling at something like ten thousand miles per hour. Luckily for Haumea and for astronomers today, the impact was only a glancing blow. Had it been more head-on, Haumea would have thoroughly shattered and dispersed to the ends of the solar system. Instead, the glancing blow left the center of Haumea mostly intact, but large chunks of the surface went flying into space, while Haumea itself was left spinning faster than almost anything else in the solar system. Some of the chunks that were blasted off the surface didn’t go far; at least two are now in orbit around Haumea as small moons (when we first discovered these we called them Rudolph and Blitzen, but now they are named after children of Haumea: Hi’iaka, the patron of the Big Island of Hawaii and the goddess of hula, and Namaka, a sea spirit). Many more of the chunks were blasted so hard that they escaped Haumea entirely and now form a virtual cloud in orbit around the sun.
It also turned out that I was right not to get my hopes up about the size of Santa/Haumea. We learned that Haumea is covered in pure ice, and it is smaller than Pluto.
None of this was obvious when Santa/Haumea was first discovered. It just looked like a normal, albeit extra-bright, object in the Kuiper belt. David was the first to notice something strange: It got brighter and fainter every two hours, a fact that he quickly surmised was due to the fact that Haumea was oblong and tumbling end over end every four hours.
Huh, we all said.
Next we discovered two moons.
Weird, we all thought.
It wasn’t until eighteen months after the discovery that the final pieces of the puzzle came together. It was around midnight at a beach hotel on the island of Sicily. Kris Barkume, another graduate student of mine, was going to give a presentation the next morning at an international conference on the subject of her Ph.D. thesis, which was a study of the many moderately bright objects that had been discovered by Chad, David, and me. One subset of these objects appeared unusually icy compared to everything else out there. I had asked her to concentrate on trying to understand what might be going on with those objects. By the midnight before her talk she had learned much, but she still didn’t really have an explanation. We sat down on the sofa in the lobby of the hotel so that she could go over her talk with me.
We kept looking at the data on the odd icy objects, and still no obvious explanation came to mind. Finally she said, “Oh, and you know what’s funny? Their orbits around the sun are almost identical.”
They are?
“Yeah, look. And you know what else is funny? Santa has almost the same orbit.”
In my scientific life, most of the discoveries come as the result of seeing something for the first time. A picture appears on my screen and I suddenly know something big is out there. I know no one has ever seen it before, and I feel that little charge. This time it was different. There was no obvious picture on the screen. We were just sitting on the sofa. But instead of a little charge, I felt a full jolt of instant understanding. It all suddenly made sense. Santa’s spin, Santa’s moons, the little icy objects flying around it: They were all caused by that one glancing blow millennia ago; the moons and the strange little icy pieces flying around were all the debris blasted off the surface in what we now know to be the largest impact in the outer part of the solar system. Ah ha!
Kris gave her talk the next day, skillfully laying out all of the pieces of the puzzle that we had just discussed the night before and reassembling them to tell the story of one of the most dramatic events in the known history of the outer solar system. Everyone gasped.
It took us years after the initial discovery of Haumea to find out all of these details. Even today we’re still studying Haumea and learning more and more. In the days following the discovery, back when Haumea was just Santa, I knew little more than that there was a big bright object out there waiting for me to study it in detail at the start of the year.
In addition to studying Santa, I had other things on my mind that New Year. Though I had pushed hard to finish looking at all of the old pictures to find really distant objects before the end of the year, I had not only run out of time, I’d run into distraction. I admit that I spent less time thinking about the science of the outer solar system than I did worrying about the science of embryonic growth and early childhood development. Hours that could have been spent staring at pictures of the night sky were spent, instead, reading about statistics of timing of childbirth and first smiles. I was still obsessed; I had just changed the main object of my obsession.
• • •
I had been at work on January 5 for only a few hours when I decided to get up and take a walk. I needed to walk down the street and get some lunch. I had some things to think about. Lunch that day was the same as lunch most every day. I went to the same busy corner just down the road from my office; I ordered the same sandwich from the bagel store; I sat staring into the same steaming cup from the coffee shop next door. I like things that stay the same. The sun was shining and the seats on the outside patio were packed and everyone was emerging for a several-day break in the record-setting rains that were pummelling southern California that winter. From my spot on the patio I could see the temporarily snow-covered peaks of the San Gabriel Mountains just a few miles to the north. To me, there is almost nothing more relaxing and serene than this particular cup of coffee drunk at this particular spot on the planet Earth at this particular moment in the year, when the winter storms have come from across the Pacific Ocean and cleared the skies and coated the mountains, and the sun, low even at high noon in the clear skies just a few days after the winter solstice, is shining on the tables outside and quickly melting the snow on the mountains beyond.
I particularly like the stability and predictability of this spot when I know that everything is about to change. I sat in this same spot staring at these same mountains in the last hour before my wedding, thinking about the future, thinking about the past, suddenly remembering that I had left my bow tie at home. It was the same spot where I sat with Diane for hours on a workday and realized that she was choosing to stay and sit with me rather than going back to work and that I had been stupid all along. Later, I sat in the same spot with Antonin Bouchez as he convinced me not to quit searching the skies. And, though I didn’t know it at the time, six months from now I would momentarily pause at this same spot—no time for sitting now!—as the last stop as I was taking Diane to the hospital for the birth of our Petunia, thinking only about the impending present and how long the night ahead was going to be.
This clear January day, one in which I watched the waterlogged people enjoy the fleeting sun and stared at the snow quickly melting on the mountains, was a day I would remember as well as those other momentous days at this spot. After sitting on the patio, drinking my coffee, and staring one last time at the mountains, I walked back to my office, sat down at my desk, and carefully composed a short e-mail that I knew would set in motion a series of events that would lead to a change in our view of the solar system. Eventually the news would spread across the planet, but, for now, I sent copies to only two people: Chad, 2,500 miles west of me on the Big Island of Hawaii, and David, 2,500 miles east of me at Yale University. They were about to become just the third and fourth people in history to know what I had known for several hours (Diane was, of course, the second) and had been thinking about as I stared at the mountains over lunch: The solar system no longer had nine planets.
When I had left home to go to wo
rk that morning, the nine-planet solar system was still intact. Sure, the discovery of Santa was exciting, but given our track record of discovering things that turned out to be smaller than Pluto, I was pretty sure that Santa would be, too. It seemed likely that the solar system would retain nine planets. It seemed likely until I sat down at my desk that morning and discovered the tenth. There it was, moving across the sky, visible on a series of pictures blinking across my computer screen. Two weeks after the discovery of Santa, the almost-planet, I had found the real thing.
There aren’t many chances in life to write an e-mail like the one I sent to Chad and David. I’d thought all through lunch about how exactly I would word it. I went for carefully calculated obscurity:
Subject: why we get up in the morning
And then I went on, staccato style:
new bright object
please sit down and take a deep breath
mag = 18.8, making it brighter than anything out there except Santa
distance = 120 AU
and, by the way, if you moved Pluto to 120 AU it would be about mag 19.7
That’s all they needed to know to understand that the solar system was, from that day on, a different place. To most people, all of this would be more or less nonsense (at least I hoped, in case there were prying eyes; I was, I thought, overly paranoid, but in the end it turned out I was not nearly paranoid enough), yet Chad and David would instantly see the significance of each of the lines.
new bright object
We had just discovered Santa two weeks earlier, and I was sure they would assume that was the object I was referring to. What else would I be writing about? No one expects the next one to come so fast.
please sit down and take a breath
Okay, I have a melodramatic streak.
mag = 18.8, making it brighter than anything out there except Santa
Astronomers describe the brightness of their objects in “magnitudes,” and “mag = 18.8” immediately told Chad and David that the new object was bright, at least for something out there in the region of Pluto. But this was only the second-brightest object we had found to date, and it wasn’t even as bright as Pluto. The next line was designed to get them to fall out of the seats that I had previously asked them to sit in.
distance = 120 AU
The phrase “120 AU” means 120 times the distance from the sun to the earth, or about 12 billion miles. Even to astronomers, the phrase “12 billion miles” generally means nothing other than “really far away.” But 120 times the distance from the sun to the earth is packed with meaning. It is farther than anything that had ever been discovered in orbit around the sun, and almost four times more distant than Pluto. Finding something at this distance was a major discovery, regardless of what it was. But something so far away would be expected to be so faint that it would be just barely visible in our telescope. This object was not just barely visible, it was almost the brightest thing we had ever discovered. The brightness (“mag = 18.8”) combined with the distance (“distance = 120 AU”) meant that I was writing about something that must be larger than anything we had found in all of the previous years of our searching. The next line of the e-mail drove the point home, in a feigned attempt at nonchalance:
and, by the way, if you moved Pluto to 120 AU it would be about mag 19.7
Pluto is much closer to us and to the sun than this newly discovered object, so it appears to be much brighter; but if you moved Pluto out to the same distance as the new object it would be almost three times fainter than the new object (which, in astronomers’ archaic system, would mean that it had a higher magnitude). If you have two objects at the same distance from the sun and one is brighter than the other, chances are that the brighter one is bigger than the fainter one. Chances were that the newly discovered object was bigger than Pluto. Chances were that the nine-planet solar system had just come to an abrupt end on that early January morning.
I pressed the “send” button on the e-mail and sat back to think about the significance. Nothing this large had been found in the solar system in more than 150 years; no person alive today had ever found a planet; history books, textbooks, children’s books would all have to be rewritten. But I don’t remember thinking any of those things. All I can remember thinking is that we were only five days into the New Year and Diane and I had, just a week before, told our parents and friends that we were expecting our first child; a week before that I had discovered Santa, which would eventually spawn the biggest astronomical controversy in years; and now I had found something bigger than Pluto.
Wow, I thought, this sure is going to be a busy year.
• • •
I sent one more e-mail that afternoon before diving in to learn what I could about the new object. It was to Sabine, the friend with whom I had made the bet five years earlier.
Would you be willing to grant me a five-day extension on our bet?
She said that she would.
By the end of the week, David had tracked the object down on some recent pictures he had taken, and Chad had followed it into the past for decades. We knew the orbit precisely. The orbit was, like that of Santa, relatively normal. It was scattered. It was so far from the sun right now only because we had caught it at its most distant point. It’s on its way back in but will take a while to get there. The object takes 557 years to go around a full orbit, so it will be half of that—278 years—before it is at its closest point to the sun. When that happens, it will be closer than Pluto and thus, presumably, brighter as seen from the earth. I can’t wait to see it.
Clyde Tombaugh found Pluto in 1930 but spent much of the following decades searching for whatever else might be out there in the distant regions beyond Neptune. He never found anything else. As the story is usually told, this was because he was using the old technology of photographic plates, which were simply not good enough to see what we now know as the myriads of objects out there. But we now know that the story is not quite so simple. If Tombaugh had been looking 278 years earlier or 278 years later, our new object would have been as bright as Pluto, and he would have found both.
It’s interesting to ponder what people would have thought in the 1930s if not just Pluto but also this new object had been found. Both are on crazy elongated orbits. Both appear significantly smaller than the giant planets. And their orbits cross. I’m pretty sure that the similarities to the asteroid belt discoveries 130 years earlier would have led everyone to conclude that these were simply the biggest members of what would turn out to be a huge population of similar objects. And they would have been right. Instead, though, the solar system was arranged such that at the time of the development of large photographic plates and the first major survey of the outer solar system, only Pluto was close enough to be seen. Too bad for us not to have been provided with such obvious clues to the nature of the outer solar system. But good for Pluto, since it got to be everybody’s favorite oddball planet for more than seventy-five years. Though it wouldn’t be for much longer.
We didn’t refer to our discovery as “this new object” for long. We quickly gave it a code name. Unlike Flying Dutchman or Santa, which were inspired by circumstances of the discovery, we had had a name waiting for this one for a long time. Since the earliest days of surveying the outer solar system with the photographic plates, I had always had a well-considered code name for the hypothetical object bigger than Pluto. In coming up with the name, I had thought that it was best to keep the X for the apocryphal Planet X beyond Neptune. And I had thought that Venus shouldn’t remain the only female among the planets. And finally, I thought that the name should be mythological.
With those criteria, I was left, as far as I could tell, with only one choice. We called the new object Xena, after the eponymous heroine of Xena: Warrior Princess, the campy, female-empowered television take on Greek mythology starring Lucy Lawless. It was true that the name Xena was only TV mythology instead of real mythology, but as I liked to point out for the next eighteen months, as the n
ame got more and more widely known, wasn’t Pluto named after a Disney dog? Whenever I made that joke publicly, about half the people in the room actually thought I was serious.
A few weeks after the discovery of Xena, Chad got a chance to swing the giant Gemini telescope, at the summit of Mauna Kea on the Big Island of Hawaii, in its direction. Chad now worked at that telescope, so getting a little time at the discretion of the director to look at something that was clearly bigger than Pluto was no hard task. When he looked at Xena’s surface, we had our first confirmation that Xena was something special. Xena looked like Pluto.
By “looked like Pluto” what I really mean, to be more precise, is that the sunlight bouncing off Xena contained within it the unmistakable signature of a surface covered in solid frozen methane. Nothing else in the Kuiper belt looked like this, with one exception: Pluto.
It was one thing to make the quick calculation to know that Xena was bigger than Pluto. But we had been looking at new Kuiper belt objects for a long time, and we had never seen anything that looked like Pluto.
I went home that night and told Diane about the methane.
“So it’s a planet?” she said.
“No,” I quickly pointed out. “It means Pluto is not a planet.”
“But if there are only two of them out there that look like this, and they both look different from everything else, why not just call them both planets?”
I went over my usual litany: Pluto was simply the largest—now the second largest!—member of a huge population in the Kuiper belt. Singling it out for special planetary status really made no sense at all.
“Okay, but think about your daughter.”
Huh?
“Having her father discover a planet might mean that someday she’ll be able to afford college.”
Diane was joking. At least mostly.