Does Titan's Slightly Oblate Shape suggest a Capture Origin?

Cassini radar observations show that Titan is slightly oblate (Zebker et al, 2009 Science 324 921). The average polar radius falls short of the expected value by 120 m. The synchronously rotating ellipsoid of uniform density that best matches Titan’s shape has a spin rate that is 1.12 times faster than the present rate. Next, a freely-spinning, uniform-density, oblate spheroid of Titan’s mass and mean size which best fits the satellite’s shape has a polar radius which equals the observed value exactly. The spin rate of this hydrostatic equilibrium object is 1.97 times the present value. These calculation are based on the theory of rotating fluid satellites developed by Dermott (1988, Icarus 37 575). The Titan shape data, along with the existence of the non-zero value of the eccentricity of Titan’s orbit, re-awaken the possibility that Titan did not originally condense in orbit about Saturn (Prentice, 1980 JPL Publication 80-80; 1984 Earth, Moon and Planets 30 209). Instead, it is suggested that Titan first condensed as a secondary solid embryo within the gas ring that was shed by protosolar cloud (hereafter PSC) at Saturn’s orbital distance from the Sun. By forming in a free orbit about the PSC, Titan’s shape would have initially been that of an oblate spheroid, like Ceres. Next, the condensate that forms in the PSC gas ring of temperature 94 K consists of anhydrous rock (mass fraction 0.4925), water ice (0.4739) and graphite (0.0336). Its mean density at 94 K is 1.5221 g/cm3 (Prentice, 2006 Publ. Astron. Soc. Australia 23 1; 2007 38th LPSC, 2402.pdf). The gravity measurements of Iess et al (2010 Science 327 1367) have revealed that the interior of Titan is in a state of incomplete separation between the rock and ice phases. The axial moment of inertia is C/MR2 = 0.342. The gravity data suggest that the interior of Titan is cold and that its structure consists of a central core of rock and ice that is surmounted by a mantle of pure ice. The non-zero orbital eccentricity of Titan also points to a cold and rigid interior (Sohl et al, 1995 Icarus 115 278). It is proposed that Titan initially accreted at low temperature (94 K) within the gas ring shed by the PSC at Saturn’s orbit. Titan’s present 2-zone structure came about through the melting of its outer layers via the dissipation of gravitational energy in the final stages of its accumulation, as has been suggested for Callisto (Lunine and Stevenson 1982 Icarus 52 14). Initially Titan was spinning rapidly and had a highly oblate shape. Titan’s capture by the Saturn system was secured by collision with one or both of 2 volatile-rich native moons of Saturn that once existed at 17RSat and 24RSat where RSat = 60268 km (Prentice 2005 BAAS 37 729). It is the NH3 and CH4 ices of those lost moons which is the source of Titan’s N2 -CH4 atmosphere. If Titan’s outer ice mantle was still warm at the time of capture, then its shape would soon relax via tidal dissipation to that demanded by the moon’s new orbit about Saturn. The shape of the cold inner core might, however, retain its oblate shape. Titan’s shape today is thus the outcome of an amazing and complex dynamical past. I present numerical models for Titan’s radiogenic evolution to solar age which show that the central core has remained cold to solar age.