Experimental investigation of methane hydrates dissociation up to 5 GPa: Implications for Titan’s interior

• We study the stability of methane hydrates at high-pressure and high-temperature.
• Raman shift of C–H mode is higher for MH-III than the one of pure solid methane.
• Methane hydrates dissociate at temperatures close to the melting curves of H2O-ices.

Methane may be present in significant amounts in the interior of Titan and other icy moons, as well as in water-rich exoplanets, potentially stored in the form of clathrate hydrates. Here we report a high-pressure investigation of methane hydrates stability using a diamond-anvil cell combined with Raman spectroscopy and X-ray diffraction. The phase changes with increasing pressure and temperature were determined using Raman spectroscopy and X-ray diffraction. Raman shifts in the C–H symmetric stretching mode signature (ν1 mode) for both MHs and solid methane were established for pressures ranging between 0.2 and 5 GPa. From the observed differences in Raman shifts and X-ray diffraction peaks, we determined the dissociation temperatures of MHs for pressures between 1.5 and 5 GPa. Our results show that, in this pressure range, MHs dissociate into solid methane and liquid water at temperatures close to the melting curves of water ices. The implications of these new results for the fate of methane in Titan and in water-rich exoplanets are briefly discussed.