So on that basis, Pluto is a planet because it's been as such in the public consciousness for almost eighty years. You can't go back on that now. So my definition is, if it orbits the sun (primarily) and it's been given a name, ipso facto, it's a planet, for the simple reason that we irrational humans have given it an identity.

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To elaborate on my above post, let me state that I am not a scientist although I do follow and take a great interest in science, especially astronomy. I am however something of a poet, and I think what's needed here is for the astronomers who are currently arguing over this definition to take a step back from their text books, loosen up a little and try to see the poetic side of the problem. They have invoked the poetic in naming an object in the first place. Let me explain.

In the subatomic world all the various particles and forces are discrete and easily catalogued, once their properties are discovered. Scientists tend to get used to the idea that everything in nature can be neatly packaged up in boxes like that, but it ain't so, especially when you get to astronomical sizes. What exactly is a planet? Where is the cut-off point between a planet and a star? Or between a planet and a lump of rock? Answer: there isn't one. It's like trying to segregate lakes from ponds, streams from rivers, islands from continents. Whatever rule you come up with, someone will disagree.

On Phil Plait's page (link above) there are some fascinating facts to be found about planets and their properties, and a lot can be learned from that. I urge anyone with an interest in astronomy to read what Phil has to say on that page. But can any of these hard facts be used to determine what is in effect, a vague human poetic term like "planet"? My answer (with my poet's hat on): no, they never will. It can't be done, and here's why. The astronomers have to realise that when they point to something in the sky and give it a name, they have stopped being scientific. They have become poetic. Once you have given something a name, you have deserted your strict scientific boundaries and shown yourselves to be "merely" human, and the upshot of that is that you can't then distance yourselves from that emotional leap and go back to trying to fit that "fact" into a pigeonhole. You deserted that pigeonhole when you named it. You're stuck with it. Live with it.

It's similar to giving an animal a name; suddenly it's not just any old animal, it's become a pet. It has gained recognition in our eyes. It has become part of the Human consciousness; part of our world view. It's not scientific, but it is poetic. Same goes with celestial objects. It's a planet if it's considered important enough to be given a name (and is obviously not anything else like a star or comet or galaxy. Of course the same rule applies to those categories.)

And if that sounds a bit vague, then sorry but that's the way it has to be. If you don't want it to be thought of as a planet then don't give it a name!