A Modest Proposal from Charlie Stross...

It will make memorizing the planets easier:

Charlie's Diary: The new solar system: Last week, the International Astronomical Union began work on a rather important counting-angels-on-the-head-of-a-pin exercise: defining precisely which bodies orbiting our sun qualify for the appellation of "planet"....

We all know that the only real planets -- the big ones that accreted from the solar disk right at the beginning -- are Jupiter, Saturn, Nepture and Uranus. They're self-accreting bodies that aren't massive enough to undergo fusion and that formed in orbit around a star. OK? That's a planet.

Naturally you're biased: you live on Earth after all. But I have to tell you, these days we have this theory called the heliocentric model that holds that Earth isn't the centre of the universe. Guess what? Earth isn't a real planet, either. It's just a ball of rocky left-overs that didn't get its fair share of gas when the accretion disk was still swirling. Indeed, the same goes for Mars, Venus, and Mercury. These tiny rocks (Earth, the largest, is barely a thousandth the mass of Jupiter) orbit in the wrong damn place, far to close to their primary star to have any hope of hanging onto a volatile envelope of hydrogen and a bit of helium. In fact, I think it's about time the IAU bit the bullet and admitted that these dwarfish rocky cores are just that, and introduced a new category, "failed planetary nuclei", to define the rocky Earthlike bodies of the inner solar system.

Given that the "Plutonoids" are believed to be mostly condensed gassy stuff, we can (subject to confirmation) then redesignate them as "failed planetary atmosphere fodder". The asteroids and small KBOs can then be allocated to one group or the other, or a fourth, catchment category: "irritating little s---". And the rationalization of the solar system is done.

It'll be so much easier to teach kids the names of the planets when we've pruned them back to four!