High-pressure neutron diffraction and models of titan

Saturn's largest moon Titan is the only planetary satellite to have a significant atmosphere. The nature of this atmosphere and the origins of the ～5% of methane in it are a source of longstanding debate. The high-pressure properties of the icy components - ammonia monohydrate and methane hydrate - from which Titan formed are crucial to modelling of Titan and yet until recently were poorly known. We have now carried out neutron diffraction studies of both systems across the entire pressure and temperature range relevant to Titan. We found several new phases in ammonia monohydrate and have been able to construct an equation of state for this material. And we have shown that methane hydrate does not decompose into ice and methane at 1.2 GPa as had been calculated. These results move modelling of Titan onto new ground.