Quote:
Probably worth pointing out how, in my quote above, the Cassini team are using several flybys for these measurements. If you catch Titan at different distances from Saturn, you get a measure of how it deforms under tidal strain: that not only gives you density-gradient information, but an idea of the viscoelastic properties, too.
That second modality is also helpful in differentiating liquid from solid.
Grant Hutchison
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They'll be lucky to get a good estimate of the J
2 gravitational moment (which is affected by how uniformly the density distribution is--the lower the J
2 is, the more uniform the density is). So while that definitely constrains the search space of plausible models, there is still a huge family of plausible models that can fit the data. The fact is we don't know the exact composition of the core--and that alone introduces enough uncertainty to swamp out any differences in density between frozen and liquid ice.
I'm not saying there isn't a liquid ocean--I bet there is. And there is some other evidence that's suggestive in that regard: the surface doesn't have a lot of cratering; apparently there's cryovolcanism; lots of nitrogen implies lots of ammonia that has a low freezing point; and if there really are liquid lakes on the surface, it stands to reason there is liquid beneath the surface as well.
But a definitive answer to the OP question would require simultaneous measurements of gravitational and topographical amplitudes of the semidiurnal tides, and to do that will require a dedicated orbiting spacecraft.
