"Magmas, i.e. silicate melts, have played a key role in the chemical and thermal evolution of the Earth and other planets. The Earth's interior today is the outcome of mass transfers which occurred primarily in its early history and still occur now via magmatic events. Present day magmatic and volcanic processes are controlled by the properties of molten silicate at high pressure, considering that magmas are produced at depth. However, the physical properties of molten silicates remain largely unexplored across the broad range of relevant P-T conditions, and their chemical properties are very often assumed constant and equal to those known at ambient conditions. This blurs out our understanding of planetary differentiation and current magmatic processes.The aim of this proposal is to place fundamental constraints on magma generation and transport in planetary interiors by measuring the properties of silicate melts in their natural high pressures (P) and high temperatures (T) conditions using a broad range of in situ key diagnostic probes (X-ray and neutron scattering techniques, X-ray absorption, radiography, Raman spectroscopy). The completion of this proposal will result in a comprehensive key database in the composition-P-T space that will form the foundation for modelling planetary formation and differentiation, and will provide answers to the very fundamental questions on magma formation, ascent or trapping at depth in the current and past Earth.This experimental program is allowed by the recent advancements in in situ high P-T techniques, and comes in conjunction with a large and fruitful theoretical effort; time has thus come to understand Earth's melts and their keys to Earth's evolution."