I swear I'll stop (planets, cont.)

Two interesting comments re: the definition of planets. First, Flocons gets the prize for wit:

This new planetary definition follows in the legacy of Esperanto. It's built around logical and unambigious rules... but in the end, the public will ignore it and use what they use already.

Second, Chris writes:

The reason the huge moons aren't now classified as planets is because they properly orbit their planet.
... It's actually a fairly nice elegant and common sense solution.

Well, kind of. What this definition strikes me as is a way to rationalize the definition of planets without changing the definition of Pluto-Charon in any way whatsoever. Which strikes me as a silly way to write what is supposed to be a label with some academic value. (Here, "academic" can be read however you like it.) I agree, Chris, that this is actually an elegant way of summing up the conventional list of planets - that is, what do all the nine common planets have in common. Nevertheless, I think the definition remain problematic.

We agree that, conventionally speaking, Pluto-Charon don't orbit the sun the same way the Earth, but not the moon, does. Rather, they orbit a point in space between the two bodies. So we've already agreed that the definition of "planet" isn't exclusive to bodies that solely orbit the Sun.

I submit that it's hard to argue that Ganymede, which indirectly orbits the sun as it is tugged around by Jupiter, is easy to distinguish from Pluto-Charon, which orbit the sun as they are tugged around by each other. Notwithstanding the IAU's distinction between "double planets", etc.

Moreover, if a body like Ceres, or UB313, are inducted in to the hall of fame, this will mean that the label "Planet" is non-exclusive, as Ceres will remain best described as a G-class asteroid, and UB313 will best be described as a Kuiper Belt ice body. So Ganymede should be able to qualify as both a Planet in its own right, as well as a satellite of a larger planet.

(Binary stars remain stars if they orbit a larger parent star, after all. Star starry star star.)

If we are making a definition of a planet that is based solely on the shape, mass, and composition of a body - without regard to its orbit - then I think it's basically impossible to define Mercury as a planet but not Ganymede, which is actually larger than the innermost planet.

And all of this needs to be kept in context - this is possibly the least important debate going on right now. But the whole idea of building a rational naming scheme with the express goal of not leaving out the last-discovered, least-known, most-insignificant planet in the solar system strikes me as silly. I have no idea why I became a partisan for Ganymede, but I did.