A new high-pressure structure of methane hydrate surviving to 86 GPa and its implications for the interiors of giant icy planets

High-pressure and high-temperature experiments on methane hydrate were performed using a diamond anvil cell under conditions of 0.2–86 GPa and at room temperature to 1000 K. In situ X-ray diffraction studies revealed that a known high-pressure structure, filled ice Ih structure, of methane hydrate transformed to a new high-pressure structure at 40 GPa, and this structure was maintained to 86 GPa. No decomposition into solid methane and ice VII was observed until 86 GPa. In the heating treatments at 50 and 86 GPa, the new high-pressure structure of methane hydrate survived up to 1000 K without decomposition.