The Planetary Society Blog
By Emily Lakdawalla
What's in a Name?
Oct. 20, 2006 | 22:54 PDT | Oct. 21 05:54 UTC
by Bill Nye
Many friends and people I hardly know ask me about Pluto. Is it a planet? Most people are somehow disappointed or angry. Pluto, they feel, has lost its status. If nothing else, it's lost its unequivocal status. The International Astronomical Union (IAU) has declared Pluto a "dwarf planet" and therefore not a true "planet." Yikes. This nomenclature will never work. They are going to have to revisit this issue, I'm sure. It's like saying a paperback book is not a true book, or something. When it comes to words, keep in mind they include more than they leave out. The word "frog" refers to an amphibious animal, a fastener for a coat, and mucus in your throat. And, we all pretty much know what we're talking about. So, the word planet may end up describing a variety of objects. Read on.
Everyone loves Pluto; kids often say Pluto is their favorite planet. This may be in large part, because Pluto has a dog. By the way, we all know that Disney's Pluto is an animal not a person, because Pluto the Dog doesn't have any clothes on. Mickey and Mini, for example, do. Pluto the Dog has led to a familiarity with Pluto the outer solar system object. Pluto the object is also mysterious. It's way out there, cold, and dark. It holds fascination for many of us.
The thing-of-it is that if Pluto were discovered today, it probably wouldn't be a called a planet. If you could somehow bring Pluto close to the Sun, it would develop a tail like a comet. Hmm. Nevertheless, when it was discovered, the word "planet" was the state of the art. And, people for a short while apparently thought Pluto might be quite large, maybe larger than Neptune. So, the word planet has stuck for Pluto.
In all scientific classification, often one must ask oneself, "Am I a lumper or a splitter?" That is, to I group things or split them off. Bear in mind that this exercise is just for humans (as far as we know). Pluto is going to be there no matter what we call it. For those of you familiar with the Bill Nye the Science Guy show, you might notice that I'm a lumper. I'm always looking for patterns and ways to generalize. And of course, I may be wrong about some things. But, let's consider the downside of calling anything with enough gravity to be a ball that orbits the Sun primarily rather than orbiting something that orbits the Sun, the way our Moon orbits the Earth. This lumping would render Ceres a planet as well as Pluto and Sedna and maybe Xena and Quaor planets. Well, that might not be so bad. Perhaps Ceres is too small to be a planet, because it doesn't have enough gravitational influence to clear its orbital path -- perhaps. But the proliferation of names I don't see as much of a problem. One has no difficulty at all meeting kids, who can name several dozen ancient dinosaurs -- not just several, but several dozen. Having a lot of planet names would or will be fine.
With all manner of objects being called planets, what value does the word have anymore? Well, it has all kinds of value, if we're allowed to add some adjectives. I find the expression "Main Plane" very useful. The traditional first eight, Mercury to Neptune would be those that are observed in the plane of ecliptic -- the main plane. Also, this expression has the charm of assonance (consecutive similar vowel sounds) akin to the baseball description of a throw from the third baseman or shortstop to first base: the toss across.
If we want to distinguish planets further, we can use further descriptors: the terrestrial planets, the gas giants, the icy crusts. All this adds meaning and pedagogy to the happy and familiar word planet. The most appealing description of Pluto might be "ice dwarf." Better yet, I'd like Pluto to be the first among a class of objects called the "Plutonian" planets. What fun would that be. There'd be a lot of planets, but still eight in the Main Plane with who yet knows how many beyond. That's the charm of Pluto isn't it. It's so far away and yet we share a star.
We've got a few years to mull this over before the New Horizons flies by Pluto and brings us to a new level of understanding. It will show us pictures which will no doubt amaze us. New Horizons will produce these images in 2015. Meantime, let's all keep thinking about an appropriate classification system. It's one more way we can consider and know our place among the planets and among the stars.
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