“Pluto, no longer considered a planet (it was the ninth until 2006), is not marked on the chart, but it would be below Neptune just outside the pink region (2,300 km diameter and 30-50 AU away).“
Do not take this the wrong way, but I am always a little confused about people feeling about the whole planet-dwarf_planet thing so strongly.
Pluto is still out there, just as it was a hundred years ago, when nobody knew it existed. And just recently, NASA sent a probe Pluto's way, that managed to amaze me, an outspoken Pluto-hater[0]: Turns out that Pluto is much more complex than people had anticipated.
Who cares what the IAU decides to call it? It is what it is. You could call a rose a turd, and it still would not smell as badly. ;-)
[0] Okay, I do not hate Pluto. I just wish NASA, ESA or whoever would send a couple of probes to Uranus and Neptune. I feel very strongly about this.
one question: Why do dwarf plants on the right have an upward sloping diameter as you get farther out? Isn't a dwarf defined by an absolute diameter cutoff (i.e. above which it's a true planet, below which it's not)? or is there a formula that takes into account distance from something?
The difference in definition between a planet and a dwarf planet is just that a dwarf planet has not cleared debris from it's orbit. So not directly dependent on the mass, diameter etc.
I'm unsure why the further would orbits require a larger size though; my guess is something to do with longer, slower orbits needing more mass to get rid of the debris.
> I'm unsure why the further would orbits require a larger size though
Stern–Levison's Λ finds a body's ability to scatter smaller masses out of its orbital region over a period of time equal to the age of the Universe scales inversely with its semi-major axis [1]. (A circle's semi-major axis is its radius [2].)
This is most simply because a wide orbit contains more volume than a small orbit.
