"The problem is, as that as we find more, that list will balloon"<br /><br />I think this is the conceptual problem. There is a fundamental assumption among anti-Pluvians <img src="/images/icons/smile.gif" /> that the list of planets should be short in number. This is entirely an historical anachronism based on a primitive concept of a solar system consisting of a star, a small number of planets in quasi-circular orbits, and some garbage-- and that's based largely on the really primitive idea of the entire heavens consisting of the sun, moon, some comets and a few wandering lights.<br /><br />The solar system is a complex place full of a myriad bodies and those who determinedly rejected the smaller ice planets with the bizarre ad-hoc "cleared its orbit" criterion seem determined to keep it simple so far as one can tell so they can recite a list of "The Planets" and keep to a simple mental model that looks like a 17th century orrery.<br /><br />The solar system consists of a star, four major gas giants and a whirling mass of other worlds composed from various proportions of rock and ices. But we ended up with a definition that (not only ludicrously only applies to our own little stellar system) but lumps the utterly dissimilar Jupiter and Mercury into the same classification, just apparently to keep things simple and keep our own tidgy planet at the "top table".<br /><br />The solar system is a complex place. The list, naturally, balloons.