http://arxiv.org/abs/1612.03664
Context: Regarding dissipation in Saturn, usually parameterized by Saturn’s quality factor Q, there remains a discrepancy between conventional estimates and the latest determination that has been derived from astrometric observations of Saturn’s inner satellites. If dissipation in Saturn is as large as the astrometric observations suggest, Mimas would migrate fast due to tidal torques exerted by Saturn. In that case its initial orbital would be located inside the synchronous orbit or even inside Saturn’s Roche-limit contradicting orbital evolution models.
Aim: Using simple structure models and assuming Saturn’s core to be viscoelastic, we suggest dissipation models which are consistent with both the latest observations and with Mimas’ orbital migration.
Method: We calculated the ranges of rigidity and viscosity which are consistent with the observed Saturnian dissipation. Within the constrained rheological parameters, Mimas’ initial semi-major axis was calculated considering the frequency dependence of dissipation in Saturn’s core.
Result: If the viscosity of the solid core is near the lower boundary to generate the observed dissipation k_{2s}/Q_s~4×10^{-5}), Mimas can stay outside the synchronous orbit and the Roche limit for 4.5 billion years of evolution, and Saturnian Q becomes less than 10^4.
Conclusion: In the case of a frequency dependent viscoelastic dissipative core, the lower boundary of the observed Saturnian dissipation can be consistent with the orbital expansion of Mimas. In this model, the assumption of a late formation of Mimas, discussed recently, is not required.
D. Shoji and H. Hussmann
Tue, 13 Dec 16
10/77
Comments: 9 pages, 4 figures, 1 table, Submitted to A&A
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