The idea of a subsurface ocean on Titan is nothing new and surfaces in the geophysics/geoscience literature every so often. For example, when Voyager I passed by the moon, it detected an abundance of only 3% (mole fraction) of CH4, which is sufficiently low to preclude the stable coexistence of liquid CH4 on the surface. Lunine, et al. ("Ethane ocean on Titan", Science, 222, 1229-1230, 1983) suggested that Titan's atmospheric CH4 may have broken down by a catalyzed photochemical reaction to C2H6, with the C2H6 stemming from a subsurface ocean; the resulting deep ocean would consist of a 3:1 mixture of C2H6 and CH4. (To explain, the dissociation steps of C2H6 involve loss of hydrogen by escape, with the postulated set reactions: 2CH4 -> C2H6 + H2 and 2CH4 -> C2H6 + 2H. The intermediate molecule C2H2 plays the role of catalysis and shielding of C2H6 from photolysis. Furthermore, CH4 would break down at a rate of 1.5*10^10cm^-2/s and H/H2 would leave the atmosphere at 5.5*10^9 and 7*10^9cm^-2/s, which is consistent with Hanel, et al.'s analysis ("Infrared observations of the Saturnian system from Voyager I", Science, 212, 192-200, 1981). As such, it is reasonable to conclude that the result is a production of an CH4-rich ocean of 1km depth and a 100-200km thick layer of solid C2H2 on Titan's ocean floor).
For additional analyses, see: F. M. Flasar, "Oceans on Titan?", Science, 221, 55-57, 1983; O. B. Toon, et al., "Methane rain on Titan", Icarus, 75, 255-284, 1988; N. Dubouloz, et al., "Titan's hypothesized ocean properties: The influence of surface temperature and atmospheric composition uncertanties", Icarus, 82, 81-96, 1989; W. R. Thompson, et al., "Vapor-liquid equilibrium thermodynamics of N2 + CH4: Model and Titan applications", Icarus, 97, 187-199, 1992.
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