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Old February 13 2013, 04:47 PM   #54
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Re: Help name the moons of Pluto

Rhubarbodendron wrote: View Post
I am inclined to agree, but then think of the asteroid belt in our solar system. There are man rather big objects in there and there are a few tiny dwarf planets. Where would one draw the line between dwarf planet and gigant asteroid?
Actually that's incorrect. There's only one body in the Main Asteroid Belt that definitely qualifies as a dwarf planet, namely Ceres. The line you're asking about has already been drawn: a body is considered a dwarf planet if it's in a gravitationally relaxed state due to hydrostatic equilibrium, i.e. if it's massive enough to pull itself into a spheroidal shape. Ceres is the only Main Belt object that definitely meets that qualification. Vesta, the asteroid visited by the Dawn spacecraft last year, may also qualify as a dwarf planet, though it's hard to be sure because its shape has been distorted by an enormous impact event in its past, so the jury's still out.

And there appear to be many more larger objects to be lurking beyond Pluto. Having more than 25 planets could indeed make our solar system a bit difficult for laypersons like school kids.
On the other hand, there are over a hundred countries on Earth and thousands of cities, rivers, mountains, etc. Should we narrow the definition of a country or city in order to make geography class less challenging?

I think the best approach for the future would be to teach about the Solar System by region: the inner system containing the four terrestrial planets and Near-Earth asteroids; the Main Asteroid Belt containing Ceres, Vesta, and countless smaller objects; the middle system containing the two gas giants, two ice giants, and their extensive moon and ring systems as well as Trojan asteroids; the Kuiper Belt containing Pluto and countless icy minor objects; the outer system containing an as-yet-undetermined number of dwarf planets, minor objects, and possibly larger planets, as well as the heliopause; and the Oort Cloud forming a vast halo around the system.

How about counting anything as a planet that revolts directly around a sun plus has an atmosphere or used to have one?
With this definition we could keep all the original planets*, exclude big asteroids and include the more interesting objects yet to be found.
We shouldn't try to find an arbitrary definition that lets us keep our old preconceptions. Science doesn't work that way. We should amend our definitions and conceptions to fit new evidence and insights.

Alidar Jarok wrote: View Post
RJDiogenes wrote: View Post
That's what makes the most sense to me. If the definition can include objects as diverse as Jupiter and Mercury, there's no reason why it can't include Plutonian objects.
Shouldn't they be Erisian objects? I'm confused at why you aren't arguing more for Eris than Pluto, since it's a more massive dwarf planet.
But there could be more massive ones still that we haven't yet discovered. It does make a certain amount of sense to name a category after the first example discovered -- for instance, T Tauri stars, or all the dinosaur species named after the location where the first fossil was unearthed. And trans-Neptunian dwarf planets are already called plutoids (although I think that's kind of a silly category because it includes all dwarf planets except Ceres and maybe Vesta).
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