Classifications should be separate for composition, atmosphere, size, orbit, origin and whatever else is needed to distinguish objects. Earth is so a terrestrial medium sized object with stable primary solar orbit. Pluto is a small sized object (I don't know the composition, but AFAIK it's neither terrestrial nor jovian) in a stable binary solar orbit or something like that. If enough objects share similar attributes, then a named class should be defined, not in reverse. There's no need to stuff everything in drawers, some things can easily be left outside if they don't match all requirements.
Separating classifications by parameters should be simple enough, but if for example they start to decide whether something should be called a planet if it's larger than 2000km, there are a couple of moons matching that description. But if they add to that that it also needs to circle the star, Pluto instantly loses its planetary status because it's a binary planet/whatever and shares its orbit with Charon.
I think that people are too used to the 9 planets that any definition will be made only to try to match that set. Not that that itself is bad, but it's possible that this definition would be made so forcefully that it wouldn't take long to be replaced again.
On the other hand, what's wrong with two sets of definitions: "astronomical" (according to attributes of individual objects) and "classical" (the existing nine planets), just as long as there's a clear difference between the two. |
