Simulating planetary interiors with a diamond anvil cell

Planets consist of several internal layers. In the Earth, these layers include the silicate-rich crust and mantle and the iron-rich core. Pressure and temperature increase with depth inside a planet. These high-pressure and high-temperature conditions cause phase transitions in mantle and core material, including melting and solid–solid crystal-structure transformations. Such transitions affect the seismic, magnetic and elastic properties of a planet. A diamond anvil cell can simulate planetary interior conditions in the laboratory. Diamonds are chosen because their hardness withstands extreme pressures and their transparency allows optical and X-ray measurements. In this device, two gem-quality diamonds (anvils) are positioned opposite each other with their culets (the flat facets at the crystal tip) facing each other. A gasket with a central hole is placed between the culets to hold the sample, which can be powder or a single crystal. Pressure is generated by turning four screws that push the diamonds together. The small culet size (~100–500 microns in diameter) concentrates the force to generate high pressures. Pressure is measured using known calibrants such as gold or platinum. Hydrostatic pressure is maintained using pressure media, such as a methanol–ethanol mixture, or inert gases, such as neon or helium. High temperatures can be generated using a laser heating system. Plank’s radiation law is used to estimate the temperature from the thermal radiation emitted by the sample. The device can then be coupled with different X-ray and spectroscopic techniques to investigate material properties.