Quote:
Originally Posted by Anthony
Any effect that elongates the planet will similarly elongate the atmosphere.
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Yep. If the planet is notably oblate because e.g. of rapid rotation the atmosphere will be deeper at the equator than at the poles, but because the centrifugal effect reduces effective gravity it will lighten the air column to just the same effect as it deepens it, resulting in the air having the same pressure and therefore density all over the surface. It has to work out that way because the geoid is an equal-energy surface, which means that gravity-cum-rotational effects will not cause air to flow over the surface, which means no pressure differences from that consideration.
That leaves, I guess, the proposition that the land surface might not conform to the geoid (the water surface has to if it's connected), but that's inconsistent with hydrostatic equilibrium in the mantle, and it would correct itself in only thousands to about 20,000 years. I suppose that it's possible that there might have been truly enormous ice-caps that weighed down the polar regions and displaced mantle material to under the topics. If such caps melted very recently (in the last couple of thousand years) then I suppose that the planet might be in the midst of adjusting from a large-scale disequilibrium. But then I think you would expect to see large polar oceans and equatorial land-masses, with the oceans about as deep as the highlands are elevated. There would be progressive flooding of the equatorial land as it sank towards equilibrium, and vigorous seismicity. Even so, I feel intuitively that the amount of ice necessary to make this effect noticeable to the extent implied is implausible. I'll have to ask a geophysicist about that. In any case, this situation is hardly compatible with there being any land at the poles.