How I Killed Pluto and Why It Had It Coming - Mike Brown [4]
But when Jane told me she had just found the Kuiper belt, I didn’t know any of this. Jane explained. She had not found this vast collection of bodies beyond Neptune, exactly, but simply a single small icy body circling the sun well beyond the orbit of Pluto. The body was tiny—much, much smaller than Pluto—and as far as anyone knew for sure, it might have circled the sun all alone at the edge of the solar system. But still, exciting, right?
Cute, I thought. But it’s just one tiny object, and it’s farther away than Pluto. How could that matter?
So I nodded and listened and, like any diligent Ph.D. student midway through a dissertation, eventually walked back down the stairs, stepped into my office, and reentered the world of Jupiter and Io and volcanoes, where I actually resided.
I was wrong, of course. Even though the object discovered was only a lonely, relatively tiny ball of ice orbiting beyond Pluto, it showed that astronomers had been wrong: They didn’t actually know everything; there were things still to be found at the edge of our own solar system. Some astronomers were reluctant to consider this new possibility seriously, and they dismissed the discovery as nothing more than a fluke that presaged absolutely nothing. But soon, as more and more astronomers became excited about the possibility of discovery and started searching the regions beyond Pluto, more and more of these small bodies began to be found.
By the end of 1999, on the foggy December night when Sabine and I were sitting underneath the Hale Telescope at Palomar Observatory and I was proclaiming that I thought there were new planets to be found, astronomers around the world had already discovered almost five hundred of these bodies in a vast disk beyond the orbit of Neptune in what looked very much indeed like the Kuiper belt. From being something that most astronomers had perhaps heard of once or twice, the Kuiper belt had become the hottest new field of study within the solar system.
Of the five hundred bodies that were then known in the Kuiper belt in 1999, most were relatively small, maybe a few hundred miles across, but a few moderately large objects had also been found. The largest known at the time was somewhere around a third the size of Pluto. A third the size of Pluto! Pluto had always enjoyed a somewhat mythical status as a lonely oddball at the edge of the solar system, but it turned out that it had more company than astronomers had originally thought.
Over the years since I had dismissed the entire Kuiper belt as not quite interesting enough to pull my mind away from Jupiter, I had actually been thinking a bit about Pluto and about those five hundred small icy bodies recently discovered in the distant solar system. By now it seemed to me inevitable that, whether anyone realized it or not, astronomers were on an unstoppable march that would eventually lead to a tenth planet. It seemed to me obvious that it was there, slowly circling the sun, just waiting for the moment when someone somewhere pointed a telescope at the right spot, noticed something that hadn’t been there earlier, and suddenly announced to an unsuspecting world that our solar system had more than nine planets.
Sitting beneath the massive Hale Telescope that foggy night, ever the scientist, Sabine asked, “What evidence do you have?”
I told her about all of the recent astronomical discoveries. But when pressed for evidence, I had to admit: I had none whatsoever. I had a hunch. Officially, scientists