The tidal history of Iapetus: Spin dynamics in the light of a refined dissipation model

Details The tidal history of Iapetus: Spin dynamics in the light of a refined dissipation model The tidal history of Iapetus: Spin dynamics in the light of a refined dissipation model

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgre..11609008c&link_type=abstract

Journal of Geophysical Research, Volume 116, Issue E9, CiteID E09008

Astronomy and Astrophysics

Astrophysics

6

Mineral Physics: Creep And Deformation, Mineral Physics: Elasticity And Anelasticity, Planetary Sciences: Solid Surface Planets: Interiors (8147), Planetary Sciences: Solar System Objects: Saturnian Satellites, Solar Physics, Astrophysics, And Astronomy: Celestial Mechanics

Scientific paper

We study the tidal history of an icy moon, basing our approach on a dissipation model, which combines viscoelasticity with anelasticity and takes into account the microphysics of attenuation. We apply this approach to Iapetus, the most remote large icy moon in the Saturnian system. Different authors provide very different estimates for Iapetus's despinning timescale, by several orders of magnitude. One reason for these differences is the choice of the dissipation model used for computing the spin evolution. As laboratory data on viscoelastic properties of planetary ices are sparse, many studies relied on dissipation models that turned out to be inconsistent with experiment. A pure water ice composition, generally assumed in the previous studies of the kind, yields despinning times of the order of 3.7 Gyr for most initial conditions. We demonstrate that through accounting for the complexity of the material (like second-phase impurities) one arrives at despinning times as short as 0.9 Gyr. A more exact estimate will remain unavailable until we learn more about the influence of impurities on ice dissipation. By including the triaxial-shape-caused torque, we encounter a chaotic behavior at the final stage of despinning, with the possibility of entrapments in the intermediate resonances. The duration of these entrapments turns out to be sensitive to the dissipation model. No long entrapments have been found for Iapetus described with our laboratory-based dissipation model.

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