Numerical Simulation of Semiconvection in Exoplanets

During recent years the research on exoplanets has evolved into one of the most exciting areas of astrophysics. Meanwhile the existence of more than 700 planets outside our solar system has been confirmed. This list of objects keeps growing continuously. There are strong indications for the existence of more than twice as many further exoplanets from the observational data collected thus far. The combination of results from ground-based instruments with observations from satellites is pivotal for the determination of basic properties, structure, and evolution of exoplanets: only the space missions COROT and Kepler (as well as MOST and in the near future hopefully BRITE and in the long-term the proposed PLATO mission) allow extremely long series of observations under optimum conditions undisturbed by the terrestrial atmosphere. The theoretical study of structure and evolution of exoplanets is immediately linked to stellar astrophysics, but has also strong relations to geophysics. This research is challenged in a completely new way by the enormous varieties of objects and stellar systems. The change of thermodynamical quantities (temperature, pressure, and density) as well as the chemical composition and the aggregate state (gaseous, liquid, solid) from the directly observable outer layers (the atmosphere of a planet and, possibly, a solid surface) to the centre of those objects is essential to understand their formation and evolution processes. The interior of planets is not accessible to direct observations and as in stars the numerical, hydrodynamical simulation takes a key role in their investigation. The research project "Numerical Simulation of Semiconvection in Exoplanets" is supposed to study by means of such numerical, hydrodynamical simulations for gaseous giant planets the role of convective processes in mixing of matter within planets and of heat transport which is responsible for the gradual cooling of planetary interiors. Specifically, the following problems are to be investigated: are the models of layered semiconvection which are inspired by geophysics also valid in the parameter space of gaseous giants, especially in shear flows and for the case of realistic microphysics? How efficient is the transport of material in layered semiconvection? Can it be represented sufficiently accurately by parametric models? Are these models also valid in case of rapid rotation of an object? The knowledge gained from the numerical simulations is hence expected to contribute to the improvement of physical models of structure and evolution of gaseous giant planets and therefore in particular of many of the exoplanets known thus far.

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