How I Killed Pluto and Why It Had It Coming - Mike Brown [82]
All of this planet-or-not-a-planet business would eventually be decided by the International Astronomical Union, which, by international agreement since 1919, has the right and the responsibility to make sure that everything in the sky is categorized, named, and filed in its right place. Before the IAU came along, the skies were filled with objects named by whatever system the astronomers categorizing them chose. The reddish star in the upper right of the spectacular constellation Orion is known not just by its common name Betelgeuse, which in Arabic means “armpit of the giant,” but also by HD 39801, for its place in Henry Draper’s catalog from the 1920s, and by many more names, including PLX 1362, PPM 148643, and my favorite, 2MASS J05551028+0724255, in other catalogs. The IAU now has procedures and policies for what to do about almost every type of discovery in the sky. A new supernova explodes? It gets a year and a letter. Supernova 1987A was the closest and brightest in living memory, and those five characters can still provoke a glowy sigh in an astronomer of a certain age. The procedure is much more systematic, though the names are not quite as evocative as giants and armpits.
Only with the solar system does the IAU require history and poetry when it comes to naming things in the sky. By IAU decree, the moons of Jupiter are to be named after the consorts (voluntary or otherwise) of Zeus, craters on Mercury are to be named after poets and artists, and features on Saturn’s gigantic moon Titan (and I can only call them “features” because we have no idea what they really are) are named after mythological places in literature.
The IAU was quick to act after the discovery of the first objects out beyond Neptune in the Kuiper belt. Things way out are named after creation gods in world mythology, though as the number of objects in the Kuiper belt grew faster than new creation gods, the rule began to be applied more and more loosely. Recently someone even got away with calling something in the Kuiper belt Borasisi, which is a god from a fictional story by Kurt Vonnegut.
For all of its preparedness for endless contingencies and countercontingencies, the IAU had never actually contemplated a question that was suddenly on everyone’s minds: What do you call something new that is bigger than Pluto? How do you recognize a new planet when you see it?
Like any good international organization, it knew what to do when faced with such emergencies: It needed to form a committee. Better yet, it already had one. At about the same time that Xena was discovered and astronomers (and everyone else) began to try to figure out how small the smallest planet could be, astronomers were also struggling with the question of how big the biggest planet could be. We had it easy in the solar system; it was unlikely that I would ever find anything bigger than Jupiter that needed to be categorized, but discoveries of things larger than Jupiter orbiting around distant stars were beginning to become routine. Some were about as massive as Jupiter or only a little more so. They were clearly planets. Some were only somewhat less massive than the sun. Those were clearly stars. Some were in between. What to do? The IAU formed a committee to decide. This same committee was now charged with figuring out the small end of planets, too.
When the reporters called to talk about the discovery of Xena, they wanted to know where it was, how we had found it, and how big it was. We didn’t yet know the size for sure but thought it could be as much as half again the size of Pluto. And then they asked: When is the IAU going to make a decision about planets?
“I hope they’ll decide before my daughter starts crawling,” I joked when Lilah was three weeks old.
When a bevy of new reporters called after the story about the Spanish snooping broke, they asked what was going to happen to the Spaniards, how the conflict was going to be resolved, and how this might change the way