PerspectivePlanetary Science

Revealing Titan's Interior

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Science  12 Mar 2010:
Vol. 327, Issue 5971, pp. 1338-1339
DOI: 10.1126/science.1186255

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The interior structure and composition of solar system bodies are key to understanding their origin and evolution. Saturn's largest icy moon, Titan, and the jovian moons, Ganymede and Callisto, are of similar size, mean density, and primordial ice-rock fraction from which the satellites formed. Titan is distinct due to its dense nitrogen atmosphere, with methane as the next most abundant constituent, which precludes direct observations of the surface. Before the arrival of the Cassini-Huygens spacecraft to study the Saturn system in 2004, little was known about the nature of Titan's interior—information as to its origin, evolution, and the rate at which it degasses was limited. On page 1367 of this issue, Iess et al. (1) report evidence based on the analysis of its gravitational field that the interior was much colder than previously thought, and thereby impeded substantial melting and subsequent separation of the primordial ice-rock mixture.