by Spider » Thu Jul 16, 2015 10:09 am
I don't think its much to do with arbitrary measurements of specific objects....more a matter of establishing classes of objects. Regardless of size or orbit, being a big half dirt clod, half snowball, Pluto has a lot more in common with all the other Kuiper belt objects than with any of the planets. Or even most of the moons. Any number of the Jovian or Saturnian moons are much more closely related to Mercury than they are to Pluto. There's some good reasoning behind these classifications. Pluto just happened to be the first big chunk we discovered out there.