Definition of a planet

lal_truckee wrote:
He's talking strength of materials, you're talking geometry. You are
talking past each other.

I'm not sure about that. I'm not talking solely about geometry; after
all, strength of materials is part of the reason I don't think you can
formulate this definition precisely.

I'd say spherical within a few tenths of percentage points of the
equipotential surface defined by a specific gravity envelope. For earth
we have Everest and the Marianas Trench each of which deviate from the
equipotential surface by less than 1/10 of a percent of the diameter of
the planet. Mons Olympus is taller and Mars is smaller - maybe a 2/10 %
deviation (someone check me!) But that's the idea. I think it's a sound
definition component, coupled with independent orbit around Sol, and
we're onto something.

How is "a few tenths" either precise or non-arbitrary? That's the
problem I have with the definition. Not to say that other definitions
aren't also similarly freighted with problems; they are. And I will
go along with David so far as to say that sphericity is a promising
direction. But he seems to think it's essentially a done deal. Maybe
I've misread him in that regard, but he seems awfully confident about
the definition.

--
Brian Tung
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