Planetary Original Diagnostics at Extreme Conditions with Raman Spectroscopy

The scarce information we have about Giant planets comes from telescopes, which see electromagnetic radiation; space missions, which observe only the planetary surface; and computational simulations. Through the development of this fellowship, we will create and study planetary materials under extreme conditions in our laboratory. For the first time, we will know what our solar system is made of.

A diamond anvil cell (DAC) is a versatile and simple device, in which pressures of 1 million times above the atmospheric pressure and beyond can be generated by pressing a tiny sample between two diamonds, (10^8 ml). DACs will be coupled to resistive and laser heating, which allows us to reach conditions close to the Giant planets outer layers. Chemistry is different at these pressures and does not follow traditionally expected routes.

Pressure causes extraordinary changes in the properties of matter by bringing the atoms closer and closer to each other. It can turn the air we breath into a beautiful dark red crystal (oxygen), make a semiconducting polymer out of nitrogen or transform peanut butter into diamond. When we misunderstand the nature of planetary materials, then all our models of planetary dynamics will go awry.

The main elements of interest in this project will be hydrogen and helium which constitute over 87 % of Giant gas planets' mass, and water, ammonia and methane, the main mantle constituents of the "icy planets" (Neptune and Uranus). These planets have strong magnetic fields, created by dynamo mechanism. In the case of Jupiter metallic liquid hydrogen drives the dipole moment, while in the case of Uranus its dynamo is thought to be due to super-ionic water.

Conductivity in these molecular fluids is induced by the extreme pressure and temperature in the planetary mantle, which ranges from 20 GPa and 2000 K to 600 GPa and 7000 K.

The aim of this project is to understand the role of hydrogen within the planetary interiors: this is expected to be in a metallic fluid state. However, it is not known whether it will be interacting with helium or if it will be able to penetrate the water, ammonia and methane layers of Neptune and Uranus forming new chemical structures or accumulating as fluid impenetrable drops.

Raman spectroscopy is an effective technique which gives access to the physico-chemical properties of matter. Coupled with diamond anvil cell technique it opens up a perfect window into the unusual world of extreme conditions at which planetary materials exist. A novel part of the project will be the fast high-temperature isothermal compression achieved within a novel devise called dynamic diamond anvil cell, to avoid problems of sample time-based reactions, characteristic of hydrogen, helium and water related materials.

This project will implement the most modern advances of Raman spectroscopy at the same time utilising my skills and experience.

This is a multidisciplinary project binding material, physical, planetary and chemical sciences. The FLF will enable me to make the first measurements of phase transformations in material behaviour at conditions relevant to Jovian planets. The astrophysics community will benefit from solid experimental proofs of the behaviour of fundamental elements in planetary conditions.

The condensed matter field, on the other hand, will be extended with knowledge of the novel materials created at extreme and brought back to ambient conditions. Therefore, this project entails a unique link between different scientific branches, namely astrophysics and material sciences. These experiments would put the UK in the forefront of extreme conditions and astrophysics sciences.

The expanding number of research groups interested in high-pressure science will benefit directly from the in-house, high-pressure facilities planned (and existing), their future development and their adaptability to their problems.