A number of compounds crystallise in the NH3-H2O-CO2 ternary system, including ammonium carbonates and carbamates, these being closely related to the water-deficient compound urea. NH3, H2O and CO2 are abundant in interstellar and planetary ices so we expect carbonates and carbamates to occur in the interiors of icy planetary bodies.Our objective is to obtain high-pressure information on the structure and properties of ternary NH3-H2O-H2O compounds to provide the basis of accurate planetary interior models. The proposed experiment complements recent ab initio calculations that show extreme elastic anisotropy (specifically, negative linear compressibility).Here we propose to compress deuterated ammonium carbamate to order 10 GPa using the Paris-Edinburgh press on PEARL, which we hope will confirm our DFT calculations and reveal the existence of any high-pressure polymorphs.