15 July 2015 - planet definitions

traditional definition: I grew up being told it was a planet.
problem: That ain’t science.

current official definition: It orbits the sun and has cleared its neighborhood of planetesimals.
problem: Extrasolar planets—aren’t.

wider definition: It has cleared its neighborhood.
problem: We still don’t know about extrasolar planets.

future definition: We’ve been calling it a planet.