"Prepare yourself—the Pluto debate has returned, and people are not going to be
able to shut up about it. Pluto might be about to regain its planethood.

It might feel like scientists are jerking you around. A decade ago they all
decided that Pluto wasn’t a planet—it was actually a dwarf planet—and now all of a
sudden they want to change it back? Maybe you even think that this just goes to
show how meaningless it all was to begin with. Planet, dwarf planet—it’s all a
made-up system determined by some esoteric group anyway.

But categories do matter, and so do the definitions we use to arrive at those
categories. The fact that people (even experts like the scientists at NASA) go
back and forth on what definitions we should use doesn’t make them less
meaningful. It just means that we’re still learning. That’s what science is all
about: we have to be able to adjust our definitions to fit our understanding. And
this whole Pluto business is a perfect example."

See:

http://www.popsci.com/pluto-might-be-planet-again