"we are using both mass and distance from the Sun (more specifically, M^2 / A^1.5, where M is mass and A is distance from the Sun). That combination of mass and orbital radius gives the average time for a body to "clear its orbit". Trying to understand the argument against Pluto a bit more and did the shallow internet search for the "Stern-Levison parameter" . If I understand the equation correctly Pluto would be a planet if it were withing 0.8 AU because it would be whipping around so fast even it's puny scattering ability would have had time to clear smaller bodies over a "long period of time" whatever that is. So if it were in Mercury's orbit it would be a planet (well for about 3 seconds until it evaporated) but way out on the edge it isn't. I'm thinking for the solar system a long time may mean something else than it might to us which apparently means from the formation until now..... Is that really the deal here? Seems dumber than I thought already.