I understand your question to be why is it important to have a category labeled "planet".
Clearly there are a variety of properties that can be observed; some bodies have some; some have others.
It seems to me that the answer to your question is, what are we going to ask school kids to learn about as common knowledge that corresponds with what we now call "planet". That doesn't seem to be the question pompe answered; he seemed to answer what he felt ought to be the characteristics shown by bodies important enough to be called "planet". I must say, I find it hard to argue with him.
The other side of the coin: one characteristic used by the IAU was that the body be large enough so that gravity dominates its shape; it makes it round. That seems an important characteristic, and one that pompe doesn't mention. I think the ones that he does mention wind up being more restrictive. Since we can detect much smaller bodies in our vicinity it seems a reasonable criterion.
But I wonder how much of the final decision was reluctance to let the public off the hook at all? We've made them learn nine; by golly, we're not going to let them get away with learning less. ;<)
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Clearly there are a variety of properties that can be observed; some bodies have some; some have others.
It seems to me that the answer to your question is, what are we going to ask school kids to learn about as common knowledge that corresponds with what we now call "planet". That doesn't seem to be the question
The other side of the coin: one characteristic used by the IAU was that the body be large enough so that gravity dominates its shape; it makes it round. That seems an important characteristic, and one that
But I wonder how much of the final decision was reluctance to let the public off the hook at all? We've made them learn nine; by golly, we're not going to let them get away with learning less. ;<)