So, What’s the Beef?

It’s been great fun reading all the comments in various blogs and listservs about the continuing process of recategorizing the places in the solar system. I think such “sorting” is a step in the right direction, and I’ll get to why in a moment. For some folks, however, the IAU’s recent action to further clarify some dwarf planets as Plutoids, including Pluto, is a slap in the face of “tradition” (the one that says Pluto is a planet and all’s right in the universe). I guess I can see why they might want to stick with that tradition, although none of the arguments I’ve heard really convince me that Pluto’s categorization is a bad one. The IAU is doing what needs to be done when you are confronted in science with multiple things (moons, planets, animals, plants, etc.): taxonomy.

Let’s think of it this way: suppose you have a bag of marbles of five different sizes and colors. You are given the job to sort and name them. So, you make five different subcollections according to size. Just to keep it simple, all marbles of each size are the same color. So, you end up with a pile of tiny pink ones, some little red ones, some middle-sized yellow ones, some rather large clear ones, and some huge blue ones. You name them Huge Blues, Large Clears, Middling Yellows, Little Reds, and Tiny Pinks. You would be foolish to pick up and say, “Well, this Tiny Pink really looks more like a Red, so I’m going to call it a Little Red, instead.” It wouldn’t logically fit in your taxonomy, although calling it a Little Red might make YOU personally feel better…

Anyway, this is the kind of “sorting” into bins that IAU is doing with the “places” of the solar system. They do it because sorting of things (classifying them) is a way of keeping “like” things together. Good taxonomies grow as the collections of “things” they categorize grow, and they help the scientists who use them characterize and study the objects they contain.

The problem of the “wrong” sorting bin for Pluto came about because we just didn’t know enough about our solar system when Pluto was discovered, and our rather old-fashioned taxonomy was simpler than that bag of marbles. We had planets, asteroids, comets, moons, and dust. Then, as solar system exploration (and the tools we do it with) got better, we found all kinds of things in between those bins — ring particles and worlds that were either bigger or smaller than the criteria we used to lump things into the original categories. Not only that, but we used to lump the worlds of the solar system into two “made out of” categories: rock and gas. Now we know that there are worlds out there that are ice, and that some of those also have rock, and that some of the gas giants could also be thought of as ice giants.

Taxonomy is a big step toward “sorting” the solar system by a number of different criteria. It may seem rather “bookkeeperish” of the IAU, but what they’re doing is allowing scientists to group worlds together by their evolutionary paths (among other things), which helps us understand the history of solar system evolution. And what we learn can be applied to planetary systems we find around other stars to help us understand their formation and evolution.

So, I don’t have a problem with the taxonomy the IAU is slowly putting together for the solar system. It actually shows that we’re learning more about our neighborhood and that there’s still a lot left to learn.