"take a bunch of M&M's scatter them on you're desk then push all the ones in the center out, you get a big high density belt and a steep drop off due to that hi

"take a bunch of M&M's scatter them on you're desk then push all the ones in the center out, you get a big high density belt and a steep drop off due to that high density." Huh? The whole issue is that it looks like it's been pushed from both sides. We know what pushed it from the inner, what pushed it/limited it from the outer? Here's a good visualisation of the edge: http://www.cfa.harvard.edu/iau/lists/OuterPlot.html http://www.cfa.harvard.edu/iau/lists/OuterPlot.html Density + mass v. orbital AU / period: http://en.wikipedia.org/wiki/File:TheTransneptunians_73AU.svg http://en.wikipedia.org/wiki/File:TheTransneptunians_73AU.sv... "Pluto got de-ranked for a whole suite of things beyond it's local orbit" Well, I'm just going by what the IAU says, I can't speculate as to the rest of it. I don't have any particular emotional attachment to the notion of Pluto being classed as a planet or not, or whether we have hundreds of the things. I think Pluto is still regarded as a kind of "honourary planet" in practise. Anyway there's plenty of other stuff in resonant orbits, especially at 2:3 and around 4:7, so again Pluto's influence seems likely to be minor. Pluto might be the local actor but it's Neptune providing the periodic "kick". "possibly there and missed isn't anywhere close to necessary to explain physical phenomena" You're the first person I've heard claim there isn't anything to explain. This is a recognised phenomenon and the consensus is we don't know the answer. Hence the need for these theories to explain it.