The first observation of ‘plastic ice’ reveals unusual behaviour of water molecules

Neutron-scattering experiments have revealed a predicted high-pressure phase of ice called ‘plastic ice VII’, in which molecules form crystals, as they do in normal ice, but rotate as in liquid water. These data highlight the role of hydrogen dynamics in defining exotic ice phases and could have implications for the geodynamics of icy planets. Plastic ice VII is an exotic phase with characteristics of both ice and water.