Pluto resonance causing demotion

“When the Earth had Two Moons”, Erik Asphaug, is a great book I gladly recommend, but...

He claims that Pluto’s resonance with Neptune is how Pluto failed the IAU planethood requirement, but I thought Pluto’s small mass prevents it from clearing out the other bodies in its orbit. Remove Neptune and Pluto still is too small, regardless where it’s new orbit finds as home.

What am I missing?


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