Why is Pluto not a Planet?

For the final part of the planet-related posts inspired by Mike Brown's book, here is his own explanation of the rationality of an eight planet solar system:

Many astronomers, tired of the endless debates before and after the demotion of Pluto, will tell you that, in the end, none of this matters. Whether Pluto is a planet or not is simply a question of semantics. Definitions like this are unimportant, they will say. I, however, will tell you the opposite. The debate about whether or not Pluto is a planet is critical to our understand of the solar system. It is not semantics. It is fundamental classification. 

Classification is one of the first processes in understanding something scientifically. Whenever scientists are confronted with a new set of phenomena, they will inevitably, even subconsciously, begin the classify. As more and more things are discovered, the classifications will then be modified or revised or even discarded to better fit what is being observed and what they are trying to understand. Classification is the way that we take the infinite variability of the natural world and break it down into smaller chunks that we can ultimately understand. 

So how should we classify the solar system? It's hard because we are sitting in the middle of it and have known planets our whole lives. But let's try to do it from the perspective of someone who has never seen a planet before. Imagine that you are an alien who has lived your whole life on a spaceship traveling from a distance star to the sun. You don't know that planets exist. You don't even have a word for planets in your language. All you know is your spaceship and the stars you can see surrounding you. The sun - which originally looked like any other star - now gets brighter and brighter as your destination nears.  

As you start to stare at and wonder about the sun, you suddenly notice that - wait! - the sun is not alone! You see that there is something tiny right next to it. You're excited beyond alien words. As your spaceship gets closer and you look even more carefully, you suddenly realize that there are two tiny things next to the sun. No, three. No, four! 

You have just found the things we call Jupiter, Saturn, Uranus, and Neptune: the giant planets. From your perspective, still quite far from the solar system, they look tiny and so close to the sun as to barely be distinguishable. You don't have a word to describe them, so you make one up in your alien language: Itsgan. 

You keep looking for a fifth Itsgan out beyond that fourth one you found, because it seems logical that there should be more, but even as your spaceship gets closer and closer to the system, you don't see anything out there. Trust me, I understand your disappointment. 

Finally, as you get close and the four Itgsan get brighter and appear more distinguishable from the sun, you realize you were looking in the wrong place all along. there are other things next to the sun, but they are inside the first Itgsan, not outside. There are four of them, but they're much smaller than the first four you found. So you come up with a new word. You call them Itrraestles. You don't know it, but you've just found Mercury, Venus, Earth, and Mars. 

For a very long time, as you keep getting closer, there is nothing new. Finally, when you're almost on top of the solar system, you realize that between the small Itrraestles and the large Itgsan there is a band of millions and millions of tiny things going around the sun. And looking even more carefully, you see that outside the large Itgsan there is another band with even more. You can them something but I can't pronounce, but I call them the asteroid belt and the Kiuper belt. 

Nowhere in that alien brain of yours would it be likely to occur to you to take one or two or even a few hundred of the things sitting in the Kuiper belt or in the asteroid belt and put them in the same category as the big Irrarestles. Instead, you would quite rationally declare that the solar system was best classified by four major categories. And you would, I think, be correct.

The only thing wrong with our current classification of the solar system as a collection of eight planets and then a swarm of asteroids and a swarm of Kiuper belt objects is that it ignores the fundamental distinction between the [4] terrestrial planets and the [4] giant planets. So even though the aliens call them Itgsan and Irrarestles, we'll lump them together and just call them all Tsapeln. 

If you didn't notice that the alien jargon was just the scrambled forms of "giants, terrestrials, planets" don't worry because I didn't either at first - even AFTER he discussed this technique used by other astronomers for other nomenclature. As you can deduce, Pluto is just one of the many members of the Kiuper belt. When it was discovered in 1930, there was little controversy over its planetary status. Later evidence of a moon even reinforced the claim! But after Brown's discoveries, Pluto was finally put in its place. Before I conclude, I want to mention two important aspects of the book I haven't touched on: one fundamental and one personal. When Brown discovered an object now called "Haumea," another group in Spain plagiarized it as their own by tracking down its location from an online data center coming from a telescope in Hawaii. It's a shame but plagiarism truly exists everywhere: http://en.wikipedia.org/wiki/Controversy_over_the_discovery_of_Haumea.

Secondly, Brown actually got married and had a child during the course of these events!! He spent quite a bit of time writing hilarious accounts of the "scientific approach" involved in caring for Lilah:

Lilah did little more than sleep and eat and cry, which to me was the most fascinating ting in the entire universe. Why did she cry? When did she sleep? What made her eat one day and little the next? Was she changing with time? I did what any obsessed person would do in such a case: I recorded data, plotted it, and calculated staistical correlations. First I just wrote on scraps of paper and made charts on graph paper, but I very quickly became more sophisticated. I wrote computer software to make a beautifully colored plot showing times when Diane fed Lilah in black; when I fed her in blue (expressed mother's milk, if you must know); Lilah's fussy times, in angry red, her happy times, in green. I calculated patterns in sleeping times, eating times, crying times, length of sleep, and amounts eaten. Then, I did what any obsessed parent would do these days: I put it all on the Web. It's still there, at least until Lilah gets old enough to find it and is sufficiently mortified that she makes me take it down (www.lilahbrown.com).

The website actually drew an international following of people who would remind Brown to update when he missed a few days. Parents to this day email him when they stumble upon the page thanking him for keeping them sane and realizing that their baby was normal with his/her (seemingly) unusual daily habits.

I found this book to be fascinating because of the incredibly long-winded story behind what transpired to be one of the biggest discoveries in the field of planetary astronomy. It inspired me to want to read into other discoveries - not just in astronomy or even the sciences but in subjects that I've ignored to take an interest. As Brown writes himself, I hope from reading these posts you have a further appreciation of not only the actual subject of astronomy but the nerdy looking professors in the Astronomy, Physics, or any science department that seem incapable of having friendly personalities. Their published work may not seem to be interesting but they all have incredible stories of their own. This was Mike Brown's story.