Alan Boyle, author of The Case for Pluto, makes an eloquent and moving argument for the importance of thinking of Pluto — and its trans-Neptunian brethren — as full-fledged worlds in their own right.  Conceiving of them as worthy of the culturally-weighted term “planet” makes a difference in how we see our own position in the solar system:

“Never again can Pluto be the ninth planet. Or the littlest planet. Or the most distant planet. But does that make Pluto a non-planet? No way. Even before Pluto was discovered, the solar system was divided into two classes of planets: the rocky worlds like Earth, and the gas giants beyond. Pluto has pointed the way to the solar system’s third great class of planets, no less important than the other two…

“Alan Stern, the principal investigator for the New Horizons mission to Pluto, says there could be many thousands of icy worlds out on the solar system’s rim–and hundreds of them could well qualify as dwarf planets. Over the long run, that will almost certainly change the way we look at our own place in the universe. And what’s so bad about that?

“‘The original view, until 10 or 15 years ago, was that we had four Earth-like terrestrial planets, four gas giants, and the misfit Pluto. But the new view is four terrestrial planets, four gas giants, and hundreds of Plutos,'” Stern says. “‘It’s jarring, because Pluto’s no longer the misfit. It’s the Earth-like planets that are the misfits.'”