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Comment by adolph | Hacker News Reader

It seems as though Pluto's primary problem is "clearing the neighbourhood." Given Pluto's orbit travels closer and further from the sun than Neptune, does Neptune also have the neighborhood clearing problem since it has not cleared Pluto?

  In celestial mechanics, "clearing the neighbourhood" (or dynamical dominance) 
  around a celestial body's orbit describes the body becoming gravitationally 
  dominant such that there are no other bodies of comparable size other than 
  its natural satellites or those otherwise under its gravitational influence.[0]

https://en.wikipedia.org/wiki/Clearing_the_neighbourhood

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Trans-neptunian objects, including Pluto, are in orbital resonance. They owe their stable orbits to the existence of Neptune.

It’s like saying Jupiter is not a planet because the Trojans exist.

...or like saying Earth is not a planet because NEA's share our orbit.

If you have to argue that it doesn't apply to Jupiter or Earth because they are obviously planets, it implies that "clearing the neighbourhood" is a vague and not particularly useful criteria.

Except I said nothing of the sort. I said the opposite.

Jupiter, Neptune and earth in your example dominate the gravity of their orbit by locking the smaller bodies into orbital reasonances.

It’s not a vague criterium. It might be an irrelevant one if you are interested in geophysics, but it’s concrete and testable.

It’s not vague or unimportant. Clearing their orbits literally made them planets because they absorbed the mass of everything they cleared out.

> other bodies of comparable size

In addition to what other commenters said about orbital resonance: Neptune has approximately 20 times bigger radius and is about 10_000 (ten thousand) times heavier. This is comparable to difference in mass between a human and a hummingbird. Could we really call them "comparable size"? I'm not sure, this is not a particularly precise term, but I would say - no.

The "Criteria" section of that article clarifies the question. Neptune holds Pluto in an orbital resonance, which qualifies as Neptune gravitationally dominating its neighborhood. Perfect, 100% clearance is not expected anyway, since that's basically impossible in a real, dirty world where things move around.

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