This session aims at understanding deep interiors and atmospheres of solar system bodies and massive extra-solar planets, their associated internal processes and corresponding material behaviour at extreme pressures and temperatures. These will have important implications for structural models (e.g. location of layer boundaries), evolution scenarios (e.g.
demixing phenomena, diffusion), and magnetic field generation (e.g. nonmetal-metal transitions). The session will include solicited and contributed papers addressing observational, laboratory, and theoretical studies of matter under planetary interior conditions.

Included subtopics are:
(1) Ab initio simulations and laboratory studies for matter under extreme conditions
(2) Interior structure, composition, and evolution
(3) Equation of state, melting, and phase transformation at extreme states