Size and Shape of Saturn's Moon Titan

Global Analysis of Titan In its orbit around Saturn, the Cassini spacecraft passes regularly by the planet's largest moon, Titan. Using a radar instrument to peer through the moon's thick atmosphere, Zebker et al. (p. 921, published online 2 April) developed a global model of Titan. Titan is slightly oblate, so that its poles have lower elevations than the equator, which may explain why the moon's hydrocarbon lakes are located at high latitudes. Titan’s poles lie at lower elevations than the equator, perhaps explaining its high-latitude hydrocarbon lakes. Cassini observations show that Saturn’s moon Titan is slightly oblate. A fourth-order spherical harmonic expansion yields north polar, south polar, and mean equatorial radii of 2574.32 ± 0.05 kilometers (km), 2574.36 ± 0.03 km, and 2574.91 ± 0.11 km, respectively; its mean radius is 2574.73 ± 0.09 km. Titan’s shape approximates a hydrostatic, synchronously rotating triaxial ellipsoid but is best fit by such a body orbiting closer to Saturn than Titan presently does. Titan’s lack of high relief implies that most—but not all—of the surface features observed with the Cassini imaging subsystem and synthetic aperture radar are uncorrelated with topography and elevation. Titan’s depressed polar radii suggest that a constant geopotential hydrocarbon table could explain the confinement of the hydrocarbon lakes to high latitudes.