Determination of Titan's Moment of Inertia in the Cassini Mission

Details Determination of Titan's Moment of Inertia in the Cassini Mission Determination of Titan's Moment of Inertia in the Cassini Mission

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999baas...31.1587c&link_type=abstract

American Astronomical Society, DPS Meeting #31, late abstracts, #59.22; Bulletin of the American Astronomical Society, Vol. 31,

Astronomy and Astrophysics

Astronomy

Scientific paper

Titan is a triaxial body in synchronous rotation. A great puzzle in the internal constitution of Titan is the extent and nature of its core, as required by its mean density rho =1.88 g/cm3: the measurement of its moment of inertia C is the crucial quantity to constrain its interior. The differences (C-A) and (B-A) between its moments of inertia will be determined by measuring their effects on the Doppler frequency shift of the Cassini spacecraft radio carriers during four dedicated gravity flybys. Saturn's torque on Titan's triaxial body forces a difference between its obliquity and its inclination proportional to (C-A)/C and of order 2 x 10-3. We propose a method to measure Titan's obliquity, thereby determining this ratio and, using the previous measurement, C. Since the polar displacement caused by the precessional motion is 2x 10-3RT 5 km, an accuracy of 300 m in the pole position is needed to obtain C to 5%. Cassini's SAR will map a substantial fraction of Titan's surface. Overlapping SAR strips will be used to construct a geodetic network and will provide information on the position of the pole. For higher accuracy one should use special pairs of flybys separated by an interval not close to a multiple of the rotation period; if the same region, roughly in the North/South (N/S) direction, is tracked, the sensitivity of the data to the true pole position will be greatly enhanced. This plan requires a good knowledge of the position of Cassini and Titan during the flybys, for the N/S overlapping strips method with an accuracy of 300 m or better. Radio and optical methods to determine Cassini's orbit will be investigated. For Titan, which is covered by an opaque atmosphere, we propose to use the four gravity flybys to determine the location of its center of mass.

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