The discovery of 2003 UB313, an object larger than Pluto orbiting at a far greater distance, has called back into question the debate as to what a “planet” is. The media is already dubbing it the tenth planet; but given this, 2003 EL61, Quaoar, and Sedna, my loyalties in the “Planet/Kuiper Belt Object” debate are starting to fall to the KBO side. This is surely not the last significant Pluto-like body we’ll find out there, and there’s a good chance Pluto is simply just another one of these objects, icy spheres with highly eccentric orbits a great distance from the sun. If that’s so, it can’t rightly be termed a planet, unless we’re willing to start calling every large KBO a planet as well. We’ll have dozens of “planets” before we’re done cataloguing all these objects. Yet I can’t bear to relegate Pluto, with all its historical significance, to a nomenclatural dung heap.
Currently, “plutino” is used to refer to Pluto-like bodies in the outer solar system with a 3:2 mean motion resonance to Neptune’s orbit. If we want to properly distinguish planets from large, rocky, icy orbital bodies, while also maintaining Pluto’s stature as the first of these bodies to have been found by modern astronomy, I suggest we expand the term “plutino” to cover KBO’s and trans-Neptunian objects and such. It’s a nice, compact word, and it somewhat simplifies our understanding of the outer solar system. I’m not sure our current astronomical taxonomy for the local neighborhood needs further complication in the way it classifies and labels various objects anyway.