Quote:
Originally Posted by grant hutchison
Radial density gradient. The "radial" modifies the "density gradient". Signifying, "how rapidly the density changes along a radius"; in this case, a Titan radius.
Grant Hutchison
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Gotcha. (And by "ELF" I assume you mean extremely low frequency radio waves.) But the density probably changes in a discontinuous, step-wise fashion. Most simple models of such moons assume a three layer structure: a rocky core surrounded by a silicate mantle, that is in turn surrounded by an "ice" shell ("ice" is a catchall word in planetary science referring to heavier volatiles like water, methane, and ammonia--as opposed to H
2 or He--that doesn't necessarily imply solidity).
Titan is probably typical in that regard, so it's almost certain that Titan has an icy shell--the question is whether it is liquid or not. And while gravitational measurements can say whether Titan has an icy shell or not, such gravitational measurements cannot settle the question of whether that icy shell exists in a partially liquid state--as they cannot for Europa.