The Pluto thing really bugs me. The only reason they came up with the new definition of a planet is because they had insisted for so many decades there was no 10th planet... and then they found the 10th planet (Eris). So before they made their announcement, they invented an arbitrary definition of “planet,” demoted Pluto, and then avoided the embarrassment of “there’s your tenth planet, right there, suckas.”
A planet should be any body large enough to be rounded by hydrostatic equilibrium that revolves independently around the sun. Making the definition subjective on what else is in the neighborhood and NOT interacting with it is just plain stupid. “Clears its own orbit?” How often are we going to face “We thought it was an extrasolar planet, but it turns out, we found another object in its neighborhood, so never mind?”
Also rubs me the wrong way: calling any orbiting rock a “moon.” Call them “natural sattelites,” if you want, but there’s nothing apparently in common between The Moon and a big snowball orbiting Jupiter. At some point, we’re going to see Jupiter clearly enough that we’ll need some distinction between “moon” and “larger chunk of ice in a ring.”
No kidding: one so-called “moon” of Saturn is buried in the D ring and is only 150 meters.
Proposed new definitions:
“Moon” means a body that orbits around another planet and is large enough to that the effects of its own gravity are strong enough to morph solid rock into a rounded shape.
“Natural satellite” means any other natural object in orbit around a planet.
That means Earth has one moon; Jupiter has four; Saturn has five; Uranus as four; Neptune has one; and Pluto has one.
*That’s a very fancy word, necessary for a very precise definition, but it’s not so hard of a concept:
Thanks for that. Very interesting.