Titan ’ s spin , gravity , and moments of inertia
نویسندگان
چکیده
Introduction Analysis of Doppler tracking data and radar images from the Cassini spacecraft have recently provided estimates of the low degree gravity field [1], and spin pole direction [2] of Titan. We examine implications of these measurements for the internal structure and rotational dynamics of that body. We derive separate estimates of the polar moment of inertia of Titan from the degree two gravity field, under the assumption of hydrostatic equilibrium, and from the spin pole direction, under the assumption of a fully damped spin-orbit configuration, or multi-frequency Cassini state. These estimates are quite different. We interpret the gravity-derived value as the actual moment of inertia of Titan, and the larger spin-derived value as an effective moment of inertia of a mechanically decoupled ice shell. This implies a sub-surface ocean, as the decoupling agent. Gravity constraints: For a body in hydrostatic equilibrium and synchronous rotation, the imposed tidal and rotational potentials together induce changes in the mass distribution which are mainly manifest as degree two spherical harmonic coefficients in the gravitational potential [3]:
منابع مشابه
Rotational dynamics and internal structure of Titan
Estimates of the moments of inertia of Titan, as separately deduced from its gravitational field and spin pole orientation, are quite different. This discrepancy can be resolved if Titan is either not precessing as a rigid body (e.g. if the shell is decoupled from the interior by an ocean), or if the spin pole is not fully damped (e.g. due to atmospheric excitation). By the end of the Cassini m...
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Article history: Received 21 May 2007 Revised 27 December 2007 Available online 3 April 2008
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