How I Killed Pluto and Why It Had It Coming (16 page)

When I had left home to go to work 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:

And then I went on, staccato style:

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.

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.

Okay, I have a melodramatic streak.

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.

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:

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.

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 name 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.

I remained adamant.

She pressed: “Didn’t you used to joke that your definition of a planet was ‘Pluto is not a planet, but anything that I find that’s bigger is’?”

Yes. I had made that joke. But it was a joke.

Diane was in her energetic superwoman second trimester. If I was working late trying to figure out something about Xena or Santa, she would stay awake even later looking at baby magazines. If I woke up early to try to look at a few pictures of the sky
just as they were coming off the telescope, she would already be awake looking at pregnancy books. As long as she was fed, she was unstoppable.

“But really, you are going to have people arguing that it
is
a planet, and you’re going to stand up and say, ‘No no no no’? If Petunia is a really cute child, will you go around and point out that, really, she is not so cute because, well, her nose is a bit big?”

Well, only if it
is
big.

“Don’t you think it would overall be better for astronomy to have new planets discovered rather than have old planets killed?”

I think it’s better to get it right.

“But don’t you think the public would be more excited and engaged in astronomy and in science if there were new planets being discovered?”

Enough, woman who needs no sleep! It is past my bedtime! But I will ponder your suggestions in the morning when I wake up, which will be long after you’ve already risen.

As winter waned to spring, three independent trains of thought ran through my mind. If I ever got to spend more than a few hours in a row thinking about one of them, I would suddenly sit up with a start and remember one of the others and start thinking about that one, before I suddenly remembered the third, and then the process would start all over again.

The first ticking calendar was strictly biological. Petunia was getting bigger. Her bones were hardening. Her eyebrows were growing. She had a July 11 due date, and though there was not much I could do to influence anything, I could nonetheless obsess about what, precisely, a due date means. I asked anyone who I thought might have some insight. I know, for example, that due dates are simply calculated by adding forty weeks to the start of the mother’s last menstrual cycle. But how effective is that? How many babies are born on their due dates?

Our child-birthing class teacher: “Oh, only five percent of babies are actually born on their due dates.”

Me: “So are half born before, half after?”

Teacher: “Oh, you can’t know when the baby is going to come.”

Me: “I get it. I just want to know the statistics.”

Teacher: “The baby will come when it is ready.”

I asked an obstetrician.

Doctor: “The due date is just an estimate. There is no way of knowing when the baby will come.”

Me: “But of your patients, what fraction delivers before, and what fraction delivers after the due date?”

Doctor: “I try not to think of it that way.”

I propose a simple experiment for anyone who works in the field of childbirth. Here’s all you have to do. Spend a month in a hospital. Every time a child is born, ask the mother what the original due date was. Determine how many days early or late each child is. Plot these dates on a piece of graph paper. Draw a straight line for the bottom horizontal axis. Label the middle of the axis zero. Each grid point to the left is then the number of days early. Each grid point to the right is the number of days late. Count how many children were born on their precise due dates. Count up that number of points on the vertical axis of your graph and mark the spot at zero. Do the same with the number of children born one day late. Two days late. Three. Four. Keep going. Now do the early kids. When you have finished plotting all of the due dates, label the top of the plot “The distribution of baby delivery dates compared to their due date.” Make a copy. Send it to me in the mail. My guess is that you will have something that looks like a standard bell curve. I would hope that the bell would be more or less centered at zero. It would either be tall and skinny (if most kids are born within a
few days of their due dates) or short and fat (if there is quite a wide range around the due dates). One thing I know, though, is that the bell would have a dent on the right side. At least around here, no kids are born more than a week or two after their due dates. Everyone is induced by then.