White rust (WR) is a highly reactive material that acts as a precursor in many chemical processes. It is produced during iron corrosion and has been implicated as a key reactive intermediate in the origins of life on Earth. Our work has shown that WR would have commonly formed on the early Martian surface under low CO2, offering a simple explanation for the composition of sedimentary rocks analyzed by the MSL rover, and carrying fundamental implications for climate evolution. However, very little is known about the formation of WR, its structural evolution, and its relationship to other well studied Fe-minerals. This proposal is focused on acquiring fundamental data on the localisation of H2O and its role in defining the structure and stability of WR. This work will shed light on the formation and reactivity of this enigmatic material, and its role in countless geochemical systems.