Quote:
Originally Posted by rally
So long as the majority of the planet is made up of the same "stuff" thats OK
But of course some planets have rocky cores and liquid or gaseous outer layers
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Not necessary. The planet's orbit is defined by its total mass not its density. It does not matter what the combination of solid/liquid components are, we are only calculating an the average figure for density; and yes, Density=Mass/Volume, hence we talk of grams per cubic centimetre or kilograms per cubic metre. I would think that the orbits of detected exo-planets would relate to the combined mass of the planet and moon(s) (if any).
Robert