Editing Appendix/Ramblings/Saturn (section)

==Structure and Stability==
Excerpt from the first paragraph on p. 1050 of  [https://ui.adsabs.harvard.edu/abs/2019Sci...364.1046S/abstract L. Spilker (2019)]:
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Saturn's ring system acts like a seismograph, providing a measure of Saturn's internal oscillations (or normal modes) that directly probe the interior of the planet &hellip; and provide a means for measuring its deep rotation rate.  These vibrations, determined by Saturn's nonuniform internal structure, are probably driven by convection inside the planet, which cause oscillations in Saturn's gravity field &hellip; Preliminary modeling of the propagation behavior of this collection of waves provides an interior rotation rate for Saturn of &sim; 10.6 hours &hellip;
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See also:  
* [https://ui.adsabs.harvard.edu/abs/2014Icar..242..283F/abstract J. Fuller (2014)], Icarus, 242, 283-296:  ''Saturn ring seismology:  Evidence for stable stratification in the deep interior of Saturn''
* [https://ui.adsabs.harvard.edu/abs/2019ApJ...871....1M/abstract C. Mankovich, M. S. Marley, J. J. Fortney &amp; N. Movshovitz (2019)], ApJ, 871, Issue 1, article id. 1, 15 pp.:  ''Cassini Ring Seismology as a Probe of Saturn's Interior.  I.  Rigid Rotation''
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Excerpts from the article by [https://ui.adsabs.harvard.edu/abs/2019Sci...364.2965I/abstract L. Iess ''et al.'' (2019)], Science, Vol. 364, Issue 6445, p. 1052 titled, ''Measurement and implications of Saturn's gravity field and ring mass'':
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&hellip; the mass distribution inside a fluid and rapidly rotating planet like Saturn is largely driven by the ratio between centrifugal and gravitational forces.  In static conditions, the planet should rotate uniformly and its gravity field should be axially and hemispherically symmetric and thus described by zonal harmonics.''


In its final 22 orbits, the Cassini spacecraft passed between the rings and the atmosphere of Saturn.  In six of these orbits, while the spacecraft was in free fall under the combined attraction of Saturn and its rings, radio tracking from an antenna on Earth was established to measure the radial velocity of the spacecraft with</font> [high accuracy, which] <font color="green">&hellip; allowed us to determine the separate signatures from each zonal harmonic and the ring mass &hellip; We found that the measured values of <math>~J_6, J_8</math> and <math>~J_{10}</math> are so large that they cannot be matched with interior models relying on uniform rotation and plausible compositions, but they are in agreement with interior models that assume deep differential rotations extending from the equator into the interior up to distances of 0.7 to 0.8 Saturn radii from the spin axis.


The gravity measurements are consistent with a mass of Saturn's core of 15 to 18 Earth masses.
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