Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p31b1534m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P31B-1534
Other
[5418] Planetary Sciences: Solid Surface Planets / Heat Flow, [5450] Planetary Sciences: Solid Surface Planets / Orbital And Rotational Dynamics, [6040] Planetary Sciences: Comets And Small Bodies / Origin And Evolution, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites
Scientific paper
It has long been recognized that orbiting closer to Saturn and possessing a greater eccentricity might give Mimas an advantage over Enceladus in terms of tidal heating. This is clearly not the case, and is sometimes referred to as the “Mimas paradox.” There is no paradox, of course, as Enceladus’ tidal activity is maintained by its 2:1 e-type resonance with Dione, whereas Mimas and Tethys are locked in a 2:1 ii’-type resonance that simply does not force Mimas’ eccentricity. Nevertheless, the maintenance of Mimas’ eccentricity (0.02) requires either that Mimas possess low dissipation (high Q), which a priori does not seem unlikely, or that the eccentricity is not primordial, and thus decaying. What could be origin of Mimas’ eccentricity? 1) It could be primordial, a relict of the accretionary epoch. It would be preserved for 4.5 x 109 yr for high enough Q (>>100). For a Maxwell viscoelastic Mimas, Q > 103 for T < 230 K. Thus, although Maxwell dissipation in a cold, inert Mimas would be very low, in this situation other sources of dissipation probably prove more important, i.e., dissipation due to transient creep mechanisms or frictional losses in the tidally worked surface regolith. Scaling estimates indicate tidal stresses of order 10 kPa at present, a dissipative surface layer ~100 m thick, and a resultant global Q of ~500-1000. 2) Mimas’ eccentricity could be the result of a massive impact. But even the most favorable case, a head-on cometary collision, would require an impacting body ~60-km across (half the size of Mimas’ largest extant crater, Herschel), which would have been catastrophic for Mimas. 3) Mimas’ eccentricity could be the result of one or more resonant passages with other midsize satellites in the past, as argued by Meyer and Wisdom (2008, Icarus 193). In their models Mimas does not necessarily have a very low Q, and substantially higher eccentricities are characteristic of the past. Sustained surface heat flows of several mW m-2 appear possible, well in excess of the long-term radiogenic contribution. Such heating might be responsible for Mimas’ nearly hydrostatic global shape, as well as a sintered and thus denser interior. Tidal heating today is quite modest, however, and the reservoir of remaining orbital energy available to Mimas unimportant.
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