The reality is we still don't have good definitions for these objects. > They can't, as one of the defining characteristics of a planet is having enough mass t

The reality is we still don't have good definitions for these objects. > They can't, as one of the defining characteristics of a planet is having enough mass to be rounded under it's own gravity. The problem here is that "rounded" simply means "roughly spheroid". It's an imprecise term with no rules governing how far from a sphere the objects can deviate and still be considered planets or dwarf planets. > Dwarf planets have no such restriction. It is that restriction that separates dwarf planets from large asteroids. The distinction between planet and dwarf planet has to do with whether or not the object has cleared its orbit of other debris.