How I Killed Pluto and Why It Had It Coming - Mike Brown [8]
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?
Chapter Two
A MILLENNIUM OF PLANETS
The end of the twentieth century was not actually the first time