Re: PLUTO.......Planet, planetoid, Celestial Body or what?
Oddly enough, no. They likely coalesced around a rocky core, for starters. Pluto isn't - so far as we know - essentially "a ball of rock with some snow on top". You could think of it more like "a gigantic pile of parkinglot gravel and snow mixed up randomly, but in such huge quantities that it's gravity pulled it into a sphere."
The gas giants, by comparison, are basically an earth-like ball of rock surrounded by a truly outrageous amount of volatiles. And here it is thought that you're going to find a much more diverse set of volatiles than you'll find on Pluto. The biggest thing being that's where all the Nitrogen in our solar system seems to have gone.
But Pluto almost shares more with comets than with rocky planets, gas giants or ice giants. It is a plutino, a form of Kuiper belt object. They are their own class, with their own composition, their own traits and similarities. Kuiper belt obejcts really aren't like the other planets - or even the main belt dwarfs Vesta and Ceres - at all.
In reality, the main determinant of whether or not you're a planet is a combination of size and composition. You probably can get away with being a "planet" at a smaller diameter than something might be considered a "dwarf planet" if, as a planet, you're a big hunk of rock instead of a snowball. Density matters. It is a determining factor in whether or not you've cleared your orbit of any of the really big things or whether you're just one bit of rubble amongst many.
And Pluto emphatically is "just one bit of rubble amongst many". There are a couple of KBOs out there bigger than Pluto that we know of already, and quite probably a few we don't know about as well. I think the last estimate was that there could be another 200 KBOs of approximately Pluto's size and composition.
So, if Pluto is a planet - a full bore, honest to $deity planet - then we must accept all - or at least most - dwarfs as planets. We go from a system of 8 major planets and categories of dwarf planets to a system of hundreds of planets.
Being a planet (or not) ir pretty arbitrary anyways. It's a classification designation created by humans to make it easier for humans to understand the solar system. So the surest reason that Pluto had to be demoted was simply because doing so made the solar system easier to understand.
8 planets, each largely unique, most with their own "ecosystem" of sattelites to learn about. Several dwarf planet and minor body categories each with collections of bodies that are roughly similar, most that exist less as their own separate "thing" and more as a "cloud of things" within the solar system.
That's fairly easy to understand. Certainly easier to remember and get engaged with than "our solar system was 250+ planets. Mercury, Venus, Earth....(208996) 2003 AZ, (55637) 2002 UX, (90568) 2004 GV...
If you're looking for absolutes in this decision, you won't find them. It's messy either way. But the decision to demote Pluto to a dwarf will make our solar system easier to understand for the next generation of astronomers who try to get a handle on just how diverse our little neck of the woods really is.
At the end of the day, that may be the best argument of all.