I've been listening in all day to the Great Planet Debate conference being held at the Applied Physics Laboratory. The scientific presentations have been fascinating; I especially enjoyed the one from Sara Seager describing the diversity of extrasolar planets, and the challenge of figuring out meaningful classification schemes for them.
However, once the panel discussion started, I was quickly turned off. I simply don't understand why people get so emotional about this. I think there is a reasonable level of emotion -- the sort you feel when you are participating in an argument and you think you have a good case to make -- but this debate is sparking a level of emotion in which people descend to ad hominem attacks on other people who hold divergent positions. I hate that; at the risk of sounding like a Vulcan from Star Trek, it seems to me that so much emotion is incompatible with logic and reason, and harms the process.
I think the weakest argument I heard today was that Pluto should be a planet because if we redefine "planet" in such a way that there are now only eight of them, that means schoolkids will be taught less than they were taught when there were nine planets, because they only get taught about "planets" and not the other stuff. I have two problems with this argument. First, we cannot let public policy dictate the conduct of science. Many educators will agree; one commented during today's meeting that the scientists need to just define the word based on science and let the educators sort out how to teach it to kids, and the audience applauded her.
Second, there are often concerns about only stuff that's defined in educational standards getting taught to kids. The fallacy here is that most members of the public are under the incorrect impression that educational standards are a list of facts. They are not. Content standards (that is, facts) are an important component of educational standards, but there are also standards about how science should be taught, how teachers should be taught, how science programs should be structured, and how students' learning should be measured. The overarching idea is that science should be taught as a method of understanding the universe and our place in it, not a list of facts received from experts.
Frankly, I think it's much less important for a student to be able to name all the planets than for the student to understand the basic structure of the solar system: that Earth is one of many worlds that orbit around the Sun at different distances. Each of these other places has similarities to and differences from Earth. Studying these other worlds is both fascinating in its own right and also helps us understand our own planet. And the way we study other worlds is by looking at them from Earth with telescopes and by visiting them with the spacecraft that leave Earth (most of them leaving Earth forever) to wander our solar system, serving as our eyes, ears, hands, and sometimes even noses.
That's what I would like every member of the public to understand. If they're into it, they can go on to learn more about the menagerie of planets, moons, asteroids, comets, and stuff that falls in between and makes classification difficult. But I don't think that we teach people that exploring the solar system is valuable by teaching them "My Very Good Mother Just Served Us Nuts". We do it by teaching them what it has to do with understanding our own place in the universe.
I use the word "worlds" a lot, and that's my cop-out from the debate over "what is a planet?" The reason the public gets so exercised about this definition is because it sets up a hierarchy -- "planets" are important, and anything that's not in that club is not. Scientists don't share this view. All these places are worthy of study. Some get studied more because we have better data. We didn't study extrasolar planets in the past because we couldn't see them. Now we can, and we study them. Planets have moved from being points of light, to points of light with satellite points of light; they've been joined by lots of other points of light in the asteroid belt as the planets themselves graduated to becoming resolvable disks. As long as we were confined to Earth-based observations, the sizes of solar system bodies made that hierarchy central to their study. Now, with spacecraft, we can visit objects of arbitrary size. So, many more scientists study Itokawa (which is truly tiny) than study Pallas (the second or third largest body in the asteroid belt), because we have excellent data on Itokawa and we have very little on Pallas. In fact, there could be more people working on Itokawa than are working on Neptune and all its rings and moons. No definition of "planet" is likely to include Itokawa. But it's a fascinating world worthy of study.
As a postscript, I highly recommend that members of the public who care about what kids get taught read the National Science Education Standards to see what they say. This document is not enforceable -- standards are set locally, not nationally -- but it has provided the framework for many local standards.