  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).
