Phase behaviour of methane clathrate under conditions relevant to Titan's interior

Methane clathrates are likely to be an important constituent of icy satellite interiors and a source of methane in the atmosphere of Saturn's giant satellite Titan. There is uncertainty concerning the phase behaviour of this material under the pressures which exist in Titan's interior. At room temperature, the primitive cubic low-pressure phase is though to transform to a hexagonal structure at ~ 1 GPa, and thence to an orthorhombic phase, which is a stuffed form of cubic ice, at ~ 3 GPa. However, there is evidence that the sequence is interrupted by the occurrence of a fcc phase prior to the hexagonal phase at temperatures close to the dissociation curve. Our objective is to compress methane clathrate both at room T and near to the dissociation curve in order to establish the definitive sequence of phase changes, and to obtain P-V data on those phases.