Number (1) is a quote from a person with very, very great interest in keeping Pluto a "planet".
You mean because he's with the Pluto mission? Fine. He's hardly the only one pointing out that there's a lot of junk out there in planets' orbits. There are 11,000 known near-earth asteroids. To redefine "planet", the IAU has to redefine "clear".
Also, Soter actually quantifies what "clearing its zone" means and that doesn't mean that Pluto wouldn't be there. Can you point to Soter's work and tell me what is wrong with his calculation for Neptune?
Nobody's saying there's anything wrong with his calculation; the issue is whether what he's calculating is an appropriate thing to use for deciding what's a planet. The IAU is doing violence to the meaning of the term. People using the word "planet" in assertions never intended to be making claims about ratios of object masses.
As for (2), if you follow Soter's work, you see that when quantified, his parameters show a distinct separation between the 8 major planets and everything else. By at least 2-3 orders of magnitude.
Over 4, actually. And he picked the middle of that gap -- 100 -- as the cutoff. So what do we do about solar systems that don't have that giant gap? When we find some other star that has a "dwarf planet" with mu=90 and "planets" with mu=150 and mu=50,000, we'll say there's a distinct separation between the dwarf planet and the planets?
And what do we say about objects with mu=1? 3 times clearer neighborhoods than our current dwarf planets; 24,000 times less clear than our planets; 100 times less clear than Soter's cutoff. Definite dwarf planets, I guess. Back around the time of the Late Heavy Bombardment, Uranus and Neptune shared an orbital zone, and may well have swapped positions. That means they both had mu about 1. So according to Soter's criterion, at that time they were both "dwarf planets", even though they were over 10 times the size of the Earth.
Now, you can say that perhaps he has picked the parameters of interest in such a way to end up with 8 planets and Pluto not a planet, and that may be a fair point. But Soter's approach is by far the best I've seen at attempting to actually take a scientific, quantifiable approach to this question.
Quantifiable, yes. Scientific, no. According to
Wikipedia,
Clearly distinguishing "planets" from "dwarf planets" and other minor planets had become necessary because the IAU had adopted different rules for naming newly discovered major and minor planets, without establishing a basis for telling them apart.
That's not science. That's bureaucracy.
What do you think are the best parameters to use for classifying Solar System objects? Roundess/Mass (i.e., hydrostatic equilibrium) is certainly a reasonable one, as would composition and origin. The last one is probably a bit fuzzier than the others. I'm guessing with this approach we would have multiple kinds of objects: Gas giant planets (J, S, U and N), Terrestrial planets (M, V, E and M), Cerean objects (with Ceres as a planet, and the other main belt asteroids), KBOs (with Pluto and a few others as planets), Moons (some of which would be planets), comets (short-period and long-period) and Oort cloud objects. Then there are Trojan asteroids and other objects (like NEAs) that are "out of place" due to their interaction with other objects.
This approach doesn't make for a nifty mnemonic, but it's far more scientific than most of the Pluto-whining going on.
That's not bad, actually. If we simply abolish "planet" as a technical category, we can stop pushing the fiction that there's a natural hierarchical taxonomy, with terrestrial planets more closely related to gas giants than to asteroids. Is there anybody to whom Mars really seems more similar to Neptune than it is to Ceres? Sure, by adding up the masses of nearby bodies, Soter was able to discover something that Neptune and Mars share that Ceres lacks. But to have gone looking for such an arcane property in the first place just to resolve the IAU's inconsistent naming rules was wrongheaded from the get-go.
