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tokens: layer is still unknown. It may be either an ice-rock layer between a rocky core and a water-rich outer mantle, or an outer rocky core composed of hydrous silicates (Lunine et al. 2010 ; Fortes 2012 ). If a mixed ice-rock layer indeed exists in the interior of Titan, then a newly discovered high-pressure solid solution in the H 2 O–CH 4 binary system called MH-III (also CH 4 filled-ice Ih) may hinder the outer transport of internal CH 4 into the atmosphere. The formation of MH-III was first reported by Loveday et al. ( 2001a ). Contrary to what was previously assumed for the H 2 O–CH 4 system, upon increasing the pressure above about 2 GPa, at room temperature, the classical structure H cage clathrate transforms into MH-III, rather than experiencing phase separation into water ice VII and solid CH 4 . In this way the solubility of H 2 O and CH 4 is kept throughout the entire pressure range inside Titan. This is also likely true for the much higher pressures spanning water ice mantles of water-rich exoplanets, given that MH-III was found to be stable up to about 100 GPa (Hirai et al. 2006 ), and temperatures higher than 1000 K (ichi Machida et al. 2006 ). We refer the reader to Loveday et al. ( 2001b ) for a detailed description of the crystallographic nature of MH-III. If CH 4 is indeed locked in grains of MH-III, scattered within a deep ice-rock layer above the rocky core of Titan, then how much of it may be transported outward depends on the buoyancy of these grains with respect to melt pockets and the solubility of CH 4 under such conditions. Such an analysis requires thermophysical data for MH-III at the appropriate conditions. In the context of Titan-like exoplanets, previous work on the transport of CH 4 across the interior pinpointed the necessary thermophysical data and the lack thereof (Levi et al. 2013 , 2014 ). Quantifying the needed thermophysical data is the prime object of this work. In Section 2 we probe the pressure regime in a possible undifferentiated ice-rock layer inside Titan, to better pinpoint our molecular simulations and the possible role of MH-III. In Section 3 we explain our computational methods. In Section 4 we derive the thermal equation of state (EOS) and thermal expansivity. Section 5 is dedicated to the heat capacity. In Section 6 we estimate the thickness of an MH-III enriched layer in Titan’s interior, and its carbon content capacity. In Section 7 we use a 1D thermal evolution model to asses the stability of such a layer. Section 8 is a discussion, and Section 9 is a summary. 2. The Pressure Regime in the Undifferentiated Ice-rock Layer In this section we estimate the pressure at the boundary between a possible internal ice-rock layer and Titan’s inner rocky core. We consider three basic constraints for Titan, its radius, mass and normalized MOI. We adopt a layered model for the internal structure (see Figure 1 ). The outermost condensed layer is a shell composed of ice Ih with a mass density of