Re: "Pluto Now Called a Plutoid"

Bryan Derksen wrote:

Erik Max Francis wrote:
Brett Paul Dunbar wrote:
No that is actually totally wrong. The definition is entirely
unambiguous, given the sheer size of the gap. On either the
Stern-Levinson parameter or Soter's Planetary discriminant, the gap is
about five orders of magnitude.

Neither of these measures is mentioned, even indirectly, in the IAU's resolution regarding Pluto or any subsequent IAU resolutions. So, so what?

They don't mention any other specific method of measuring neighborhood-clearing either. Or several other potentially ambiguous parts of the definition, such as what it means to be "orbiting the sun" (there are various co-orbital bodies that could go either way if you play with the definition a bit). I think they assumed that most people reading their resolution would not be trying to lawyerly nitpick holes in it but would instead be more interested in the basic spirit it conveyed.

Do you know of any methods of quantifying "neighborhood-clearing" that don't make the division between Pluto and the rest obvious?

Sure, there are plenty of trivial ones. "An object has cleared its orbit if there are no orbits intersecting it (after projecting both their orbits into the ecliptic) that are greater in mass than Ceres." Or, "There are no other objects greater in mass than Ceres within 2 au." Or any number of other quantified definitions.

Why not assume that they intend one of the previously-published methods that _do_ make this division obvious, since they explicitly say in the resolution that it makes that division? Do you have some reason to believe that they picked an ambiguous definition and then made an arbitrary decision to exclude Pluto?

Since they never gave or hinted at a definition, and excluded Pluto anyway, yes.

Remember, the IAU has never said word one about what definition they were using. It's pretty obvious, because just like the other definitions, they didn't give one. (What is sufficiently "round"?) All the discussion you've carried on about _which_ definition they might have meant is pure speculation, because as you've already acknowledged, there are several.

They were giving vague measures of what it means to be a planet. But that was stupid; we all already _knew_ vaguely what it means to be a planet -- it's something that's big, round, and gravitational influential on its neighbors. The IAU definition accomplished nothing, except strike one of the previous members off the list.

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