Tom Hole wrote:
Hmmm, we might be orbiting a tad differently if our mass were significantly
different than we have guessed it to be as a semi-solid core. Talk about
global warming.

Heh.

But the mass is known from Newton's laws (from the Moon's distance and
orbital period), not from estimates based on the Earth's composition.
That composition is understood from observations of wave propagation
through the Earth's innards, and you're quite right that if the Earth
were hollowed out in any way (including like a donut), those waves would
propagate quite differently than they do in fact.

Brian Tung
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