The damping of forced librations of triaxial satellites with eccentric orbits: Consequences on the dynamics of Mimas

Gérard Caudal (1)

1 ESTER - LATMOS

Saturn's moon Mimas is a triaxial body orbiting close to the planet on an eccentric orbit, and as a consequence it is librating significantly. Libration is usually believed to enhance dissipation within a planetary satellite. In this paper Mimas’ poorly understood strong inward migration obtained by Lainey et al. (2012a) is interpreted as an effect of dissipation within the librating moon. Tajeddine et al. (2014) performed observations of the phase and amplitude of libration and proposed several interior models, from which they retained only two models compatible with observations: a solid body with nonhydrostatic core, or a 3-layer body including an inner dense core, surrounded by a water ocean and an icy solid shell. In this paper I combined three major observations: libration amplitude and libration phase observed by Tajeddine et al. (2014), and inward migration da/dt obtained by Lainey et al. (2012a). A further study by Lainey et al. (2015) however tends to indicate that the Mimas’ strong inward motion might be questioned, and therefore this paper also explores situations with smaller da/dt. Within the assumption that inward migration is mainly due to librational dissipation, the solid model with nonhydrostatic core is found to be inconsistent with the observations. In contrast, a 3-layer model including core, ocean and shell is compatible. The observations permit to determine the icy shell depth h, core equatorial flattening β_i and core pendulum quality factor Q_Pei , provided that an assumption is made concerning the core density. Due to the uncertainty of da/dt inferred from observations, the value of Q_Pei is however rather uncertain. Dissipation within the oceanic boundary layers is found to contribute significantly to the total dissipated power.

Domaines: Astrophysique [astro-ph]; Astrophysique stellaire et solaire [astro-ph.SR]

Gérard Caudal. The damping of forced librations of triaxial satellites with eccentric orbits: Consequences on the dynamics of Mimas. Icarus, 2017, 286, pp.280-288. ⟨10.1016/j.icarus.2016.10.011⟩. ⟨insu-01386420⟩