Tessenyi, M; (2014) A theoretical framework to understand the diversity of exoplanet atmospheres with current and future observatories. Doctoral thesis , UCL (University College London).

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Abstract

The exoplanet field has been evolving at an astonishing rate: nearly two thousand planets have been detected and many more are awaiting confirmation. Astronomers have begun classifying these planets by mass, radius and orbital parameters, but these numbers tell us only part of the story as we know very little about their chemical composition. Spectroscopic observations of exoplanet atmospheres can provide this missing information, critical for understanding the origin and evolution of these distant worlds. Currently, transit spectroscopy and direct imaging spectroscopy are the most promising methods to achieve this goal. Ground and space-based observations (VLT, Keck Observatory, IRTF, Spitzer Space Telescope, HST) of exoplanets have shown the potentials of the transit method. However, the instruments used in the past ten years were not optimised for this task: the available data are mostly photometric or low resolution spectra with low signal to noise. The interpretation of these --- often sparse --- data is generally a challenge. With the arrival of new facilities (GPI, SPHERE, E-ELT, JWST), and possibly dedicated space instruments such as the Exoplanet Characterisation Observatory (EChO), many questions needed to be tackled in a more systematic way. The focus of this thesis is to provide a theoretical framework to address the question of molecular detectability in exoplanet atmospheres with current and future facilities. The atmospheric components and their spectroscopic signals depend strongly on the planetary temperature and size, therefore I have simulated a significant sample of planets out of a range of sizes and temperatures, to describe comprehensively the chemical compositions that can be expected in those exotic worlds. Such simulations were convolved through instrument simulators to assess performance and limitations of current and future facilities. While my study has been inspired by transit spectroscopy with a hypothetical EChO-like space-based instrument, the methodology and results of this thesis are applicable to observations with other instruments and techniques.

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