How I Killed Pluto and Why It Had It Coming (3 page)

Even as a first grader I could see that Pluto didn’t travel in perfect circles around the sun the way the other planets did. I could see on the poster that it came close enough to the sun to momentarily pass inside the orbit of Neptune, but the poster showed only this inner bit of Pluto’s orbit. The outer parts of the orbit were so far away that Pluto would have to travel off my poster, onto my wall, out my window, and midway across the front yard toward the street before it turned around and came back in toward the sun. Even stranger, Pluto didn’t orbit the sun in the same nice flat disk that all of the other planets did: It was tilted away from the others by almost twenty degrees. On the poster, all of the other planets were represented by paintings of a global view of the surface seen from high above, but Pluto—only special Pluto—had a painting of what the planet would look like if you were standing on the surface looking back at the
tiny dim Sun. The surface of the planet was covered in icy spires. These days I realize that the artists would have had no idea what Pluto looked like and probably felt the need to make the surface look like
something
interesting, but as a first grader I was thoroughly convinced that Pluto was covered in icy spires and that they would shatter at the slightest touch by a future Neil Armstrong. Clearly Pluto was different and mysterious and potentially very fragile. It would take another thirty-five years for me to learn just how fragile it really was.

In third grade we finally learned about planets in school. Most people I know memorized their order by learning some variant of the mnemonic “My very excellent mother just served us nine pizzas” for “Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto,” but for some reason, in my school we learned one that I have never heard since: “Martha visits every Monday and just stays until noon. Period.” The “and” appears between Mars and Jupiter, just where the asteroids are, though I always suspected that that was just dumb luck. The “period” at the end, though, seemed fishy even in third grade. It didn’t seem so much as to make Pluto special, as the other odd characteristics did, as much as to make Pluto seem an afterthought or a late addition or just perhaps an undesirable misfit.

Oddly, though, for a kid interested in planets, I had never been very interested in the actual night sky. Sure, I could name some of the more obvious constellations and sights—the Big Dipper, Orion, the North Star. I could point out the Milky Way galaxy, which was actually visible in the dark skies above Alabama, and I could even convince the other kids that it really was the Milky Way they were seeing and not just clouds in the sky as they always seemed to think. Once, I even saw a real comet through binoculars when my father dragged me out of bed one cold winter night in 1973 and drove us to the top of a
dark mountain to see what was supposed to be the spectacular Comet Kohoutek but instead looked to me like a shaky little smudge and please could I go back to sleep now? But I was never one of those kids who built his own telescope by grinding mirrors from blanks or who memorized the locations of each of the nebulae hidden among the constellations or, even, who could tell you that the bright light above the just-set sun was, in fact, not an airplane but the planet Venus. I could passionately describe the rings of Saturn, the number of moons of Jupiter, the rocky plains of Mars, and, of course, the icy spires on Pluto, but the fact that these distant worlds were up in the sky above me was never really part of how I thought about them, much like when I think of Antarctica now I think of pictures and descriptions and maps, but I never really think about the fact that if I jumped in a boat, turned south, and started sailing, I would actually end up there.

I did get a telescope for Christmas when I was in the third grade—the seemingly perfect gift for a kid like me—but I could never make it work. My brother was capable of constructing elaborate LEGO structures for any purpose and could make balsa wood airplanes that looked sleek and flew straight and were painted beautifully. I was lucky if my LEGO constructions stayed together and were made of more or less the same colors. My attempts at balsa airplanes usually ended in my deciding that, really, I had meant to make that model of an airplane
wreck
, and yes, it would be fun to burn the whole thing now. Trying to make the telescope work went little better. I needed to carefully align mirrors and keep the tripod steady and adjust eyepieces, and it never worked. I think I found a single star once—though in retrospect, knowing now what a star
should
have looked like in such a small telescope, it is entirely possible that I only looked at an out-of-focus streetlight with a shaky telescope.

One night in the late fall when I was fifteen years old, I was awake late enough to find myself looking up at Orion—the one truly familiar part of my winter night sky—and I noticed that something didn’t look right. Orion is full of bright stars that make very clear patterns even for the casual sky glancer: three stars for the belt, a dagger beneath, and a quartet of bright stars outlining the rest of the body. They are among the brightest stars in their region of the sky and nearly impossible not to recognize. And yet somehow, overhead, a little to the left, there was a pair of stars every bit as bright as those of Orion that I didn’t recall ever having seen before. I was not a photographic-memory-star-pattern-recognizing kid and just assumed I had somehow overlooked them, much the way I would also overlook my allegedly lost shoes even when they were right in the middle of the floor in my room. As the months went on, however, the two stars did something extraordinary. They moved! You would have never noticed it in a single night or even in a single week. But over the months, they very slowly crawled closer together. As the winter wore on and moved into spring, the two then moved apart and then around each other in an elaborate dance high overhead, while the remainder of the stars remained fixed in their constellations. I found myself eager to go check on the stars night after night. In the winter, I would have to stay up late before they rose in the sky, but as spring came, the dancing stars were directly overhead as soon as the sun went down.

I didn’t ask or talk to anyone about the moving stars; I just silently kept track. At some point that spring, though, I came across a single-paragraph article in the newspaper describing the once-every-twenty-years close conjunction of the two largest planets, Jupiter and Saturn, which looked like two bright stars wandering near Orion. They were planets! Today, I am surprised that I could possibly have been as shocked as I was. How could
I not have known? What did I think those moving stars were? How at fifteen could I have seen something unknown in the sky and not immediately needed to know what it was?

I guess no one had ever mentioned to me that you could actually see planets in the sky overhead. As soon as I realized that my two moving stars were Jupiter and Saturn, however, it became clear: Planets were not just an artist’s conception on my poster, nor even just images sent from distant spacecraft, but they were bright points of light that moved among the stars. Imagine how you might feel if you had been looking at pictures of the Grand Canyon all of your life and passionately studying the layered geology and tracing Powell’s trip down the canyon on the first raft expedition on a topo map, and then, suddenly, while out on what was supposed to be an ordinary afternoon stroll, you turned a corner and came unexpectedly to the canyon rim and almost fell in. At that point, how could you not want to explore every corner, every tributary, and learn everything that you could possibly learn about this wonder in your own backyard?

I have been hooked on the real planets in the sky ever since. I’ve kept track of Jupiter and Saturn in their travels through the stars season after season. Each year they move a little farther east in the sky as they orbit around the sun. Saturn is so far away and moves so slowly that it takes a full thirty years to complete one orbit. Today, almost thirty years after I first noticed Saturn above, it has finally almost completed one of its transits all the way around the sky—one full Saturn year—and when I look outside at night I see that it is almost back in the same place where I first saw it when I was a teen wondering what those bright stars were that danced. With luck, I’ll get to watch Saturn trek all the way around the sky and end up in this spot once more in my lifetime, but probably not twice.

Jupiter, closer to the sun, is comparatively fast; it takes only twelve years to go completely around the sky. When it gets to where it started, though, Saturn has moved on. It takes another eight years—twenty years in total—for Jupiter to finally catch up to Saturn once again so they come close together in a conjunction just like the one I noticed when I was fifteen. I’ve often wondered about the timing of this conjunction. If I had been born a few years earlier, I would have looked up at age fifteen, but Jupiter would not yet have caught up to Saturn’s position in the sky. I would have noticed only one bright planet moving a little below Orion instead of two. Would I have noticed their dance? Would I have become the person I am today, someone whose first instinct when walking outside at night is to always look up, check the stars, look for planets, locate the moon? It’s impossible to know, but it’s always hard not to feel that in some ways, for me at least, perhaps the early astrologers were right: Perhaps my fate actually
was
determined by the positions of the planets at the moment of my birth.

Whether or not the planets controlled my fate, one thing was clear: I knew what a planet was. As a child, I knew planets from my poster on the wall. As a teen, I knew them from watching them move across the sky. And later I knew them from years of writing a Ph.D. dissertation. Nobody was going to be able to change my mind about what a planet was. Right? So then, as my friend Sabine and I were sitting inside the Hale Telescope dome at Palomar Observatory on a cloudy, drizzly night finalizing our bet about whether or not someone would find a new planet, why was it that astronomers around the world suddenly could no longer agree on a definition of the word
planet
? How could it be that even I was unsure about what would and would not count?

The end of the twentieth century was not actually the first time that the word
planet
had become confusing. The word has existed for thousands of years, and its meaning has been continually updated to reflect our continually shifting view of the cosmos. Over the millennia there have been a few major events leading to dramatic changes.

The original ancient Greek meaning of the word
planet
was simply “wanderer,” or something that moved in the sky. When, as a teenager, I first noticed Jupiter and Saturn dancing among the stars, I was seeing the sky as it had been seen for millennia and noticing that there were things that were special, things that stuck out, things that moved in a different way. As the sky slowly revolves throughout the year, the stars stay in fixed patterns while the wanderers move separately and conspicuously through the constellations of the zodiac. The ancient Greeks and Romans knew seven wanderers in the sky: the five visible planets—Mercury, Venus, Mars, Jupiter, and Saturn, which are all easy to
see if you know where and when to look—plus the moon and the sun, which both also move through the sky and were also considered planets in good standing.

In a pre-electric-light, pre-urban world, people must have been much more intimately connected with the sky and the planets. Mercury and Venus, which are close to the sun and thus only show up low in the early-evening or early-morning sky, are these days frequently mistaken for airplanes; even I sometimes mistake them. But before we became used to the idea of artificial lights in the sky, the recurring appearance of the evening or morning star would have been an obvious and spectacular event that would have been hard to miss. Mars, distinctly red in the sky, even to the naked eye, always stands out. It is no wonder that some of the earliest recorded scientific records of any sort are of the positions of the planets. Everyone would have known what a planet was back then. Planets mattered. And it is no wonder that all of our basic units of time are based on the sky: A year traced the time it took for the sun to go all the way around the sky to reappear at the same location again, while a month (“moon”-th) is about the amount of time it takes for the moon to circle the earth. The seven days of the week are even named after the seven original planets. Sunday, Mo[o]nday, and Satur[n]day are the most obvious, while Tuesday through Friday are more than a bit obscure. Tiw was an ancient Germanic god of war, as Mars was to the Romans, so Tuesday is actually Mars’s day. Wednesday is Woden’s day. Woden was the carrier of the dead—a Germanic grim reaper—fulfilling one of Mercury’s less well known jobs. Thor was the Norse king of the gods, like Jupiter, and Friday is the day of Venus in the guise of the Norse Frigga, the goddess of married love.

Though planets were so deeply embedded into many aspects of everyday life, there is no recording of the public reaction to
the first and most significant shock to the word
planet
. In the sixteenth century the idea began to spread that the sun, rather than the earth, was at the center of the universe and that the earth and the planets revolved around it. Suddenly, the wanderers were in disarray. Instead of the sun and the moon and the other planets revolving around the earth, five of them (
the planets
) went around one of them (
the sun
), while the seventh (
the moon
) went around the earth. The earth, like five of the wanderers, also went around the sun. Copernicus wrote down what is perhaps the most startling proposition of all time: “The motions which seem to us proper to the Sun do not arise from it, but from the Earth and our orb, with which we revolve around the sun like any other planet.” We revolve around the sun like any other planet! The sun doesn’t move; the earth does. The earth under our feet is like any other planet in the sky. The earth
is
a planet. What seems so obvious and ingrained in us today must have been profoundly disorienting. I’ve tried to put myself in the frame of mind of the time and tried to understand how shocking it would have been, but I’ve never come close. It is as hard for me to image an Earth-centered universe as it would have been for them to imagine anything else. Everybody thought they knew what a planet was, and suddenly, one appeared beneath their feet.