Probing Planetary Ices with Compression Experiments

• Applicant: Professor Dr. Dominik Kraus
• Subject Area: Astrophysics and Astronomy ; Experimental Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 505630685

The interiors of the ice giants Uranus and Neptune are largely composed of the light elements hydrogen, helium, carbon, nitrogen and oxygen at extreme pressures of several million atmospheres and temperatures of several thousand kelvins. These environments presumably allow the formation of unfamiliar structures, such as superionic states of water and ammonia, and exotic chemistry, e.g., the dissociation of hydrocarbons into diamond and metallic hydrogen. These processes are highly complex and, so far, cannot be modeled reliably with existing theory and simulation methods. At the same time, they are thought to significantly shape the internal structure and evolution of Uranus and Neptune and may be key to explain the unusual magnetic fields observed for both planets and to elucidate their internal heat balance. Moreover, planets of similar size and probably composition, in particular so-called “sub-Neptunes”, are found to be highly abundant outside our Solar System. Thus, a better understanding of matter at conditions comparable to the interior of ice giants is required for both better models of our Solar System and a reliable classification of exoplanets from telescope data of mass and radius.To this end, we will perform laboratory experiments to create mixtures of carbon, hydrogen, nitrogen and oxygen (C-H-N-O) at conditions similar to the interiors of ice giants on Earth using energetic pulsed laser systems. These states will then be probed in situ by both optical and X-ray diagnostics to characterize physical properties, such as equation-of-state, conductivity, diffusivity and viscosity as well as the kinetics of phase transitions and chemical reactions. The proposed project will join two highly successful principal investigators in this field for a joint effort: Alessandra Ravasio (A.R.) has pioneered liquid sample environments for high-energy laser facilities to realistically match the stoichiometric composition of the ice giants. Dominik Kraus (D.K.) has combined several in situ X-ray techniques (X-ray diffraction, spectrally resolved X-ray scattering and small-angle X-ray scattering) at X-ray Free Electron Laser facilities to precisely study chemical reactions in dynamic compression experiments mimicking planetary interiors. The proposed project will exploit the latest developments at state-of-the-art optical and X-ray laser facilities to gain a comprehensive understanding of the properties of matter in the interiors of the ice giants. The obtained experimental data will be discussed within an international collaboration maintained by the PIs, which includes experts of molecular dynamic calculations and planetary interiors modelers. This will give important guidelines for the subsequent phases of the projects and, as a final result, will bring a tangible improved understanding of a vast class of astronomical objects, from icy moons to large ice giants planets, comprising Uranus and Neptune and a wide set of exo-planets.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partners: Dr. Mandy Bethkenhagen; Dr. Alessandra Ravasio