Titan at the time of the Cassini spacecraft first flyby: a prediction for its origin, bulk chemical composition and internal physical structure
I report the results of a new set of calculations for the gravitational contraction of the proto-solar cloud to quantify the idea that Titan may be a captured moon of Saturn (Prentice 1981, 1984). It is proposed that Titan initially condensed as a secondary embryo in the same proto-solar gas ring from which the central solid core and gaseous envelope of Saturn were acquired. At the orbit of Saturn, the bulk chemical constituents of the condensate are rock (mass fraction 0.494), water ice (0.474), and graphite (0.032). The mean density is 1523 kg/m^3. Structural models for a frozen Titan yield a mean density of 2095 kg/m^3 (chemically homogeneous case) and 1904 kg/m^3 (fully differentiated 2-zone case). The agreement to one percent of the latter value with the observed mean density suggests that Titan is indeed a fully differentiated satellite. The value of C/MR^2 for this model is 0.316. It is predicted that Titan has no internal ocean or induced magnetic field but it may possess a small native dipole field of magnitude 2 x 10^11 Tesla m^3 due to thermoremanent magnetization fed by the ancient magnetic field of Saturn. Capture of Titan was achieved by gas drag at the edge of the proto-Saturnian envelope at a time when that cloud had a radius close to the present orbital size of Titan. Collisional drag was also probably an important agent in securing the capture of Titan. Perhaps Hyperion is the shattered remnant of a pre-existing native moon of Saturn that was destroyed on the arrival of Titan. Titan should thus have much the same appearance as Triton, being nearly smooth, crater-free and streaked with elemental carbon (Prentice 2004a).