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Originally Posted by freddie
since we're redifining the definitions lets do a thorough job at it - only objects that pass a certain diameter can be considered planets, while others remain planetoids.
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The problem is that such a limit would be totally arbitrary and would lead to endless debate. Don't get me wrong, personally i was in favor of the 4-class proposal, 1 class for the 4 terrestrial planets, 1 class for the 4 jovian planets, 1 class for the Asteroid Belt objects, and 1 class for the Kuiper Belt objects, in that proposal Pluto was downgraded to a Kuiper belt object. Unfortunately there were not many astromomers who supported that idea.
There was a proposal with a fixed diameter limit, that limit was 2000km, which didn't solve anything since 2003 UB313 is well over the limit, and several other Kuiper Belt objects of similar or even bigger size will probably be discovered. And setting a higher limit was unpopular among astronomers since that would have meant downgrading Pluto.
You'll notice though that in the proposal that is most likely to be adopted, the IAU makes a difference between 'major planets' and 'pluton planets' (Pluto being obviously part of the latter), and from what i've read, astronomers are also starting to use the term 'dwarf planets' for anything smaller than the 8 classical planets.
So in a way, it's a 2-class system that is being created, 1 class for bigger planets alone on their orbits, and 1 class for smaller planets belonging to debris belts.
So like i said in my first post, the general public who always want simple things can consider that there are only 8 (major) planets, plus a 'certain number' of dwarf planets that will keep growing in the coming years, which is not such a problem since the general public doesn't really care for smaller planets.
This
Wikipedia page explains how planets will be categorized… In any case, it is clear that the 8 major planets are set apart, and that Pluto is moved to a subcategory that will likely contain tens of dwarf planets.