Congratulations to Simon Schleich on his successful PhD defence!

Simon Schleich and his doctoral thesis committee. Back row: Suzanne Aigrain. Front row, from left to right: Alvaro Hacar, Glenn van de Ven, Simon Schleich, Sudeshna Boro Saikia and Michiel Min. © Anahí Caldú

What is the atmospheric composition of exoplanets? Which information can we extract from observations by the James Webb Space Telescope (JWST)? How reliable are these results?

Simon Schleich addressed these questions during his PhD research. Since the discovery of the first planets outside our solar system (exoplanets) more than 30 years ago, our knowledge has expanded to include more than 6,000 such objects. Spectroscopic observations of these exoplanets enable us to gather information about the thermochemical composition of their atmospheres. The knowledge gained from this can be used to answer questions about the physical processes in the atmospheres of exoplanets, such as cloud formation or the course of chemical reactions. It also enables us to get to the bottom of broader questions regarding the formation and evolution of exoplanetary systems.

To characterise the atmospheres of exoplanets, we use Bayesian statistical methods. These methods require us to analyse the underlying spectroscopic observations robustly. In his research project, Simon investigated the extent to which uncertainties in this analysis process influence the derivation of atmospheric characteristics of gas giants. To this end, he produced the atmospheric spectrum of the exoplanet WASP-39 b. The reduction of JWST data is a complex process comprising many individual steps. By comparing results obtained from slightly different spectra, he has shown that certain derived atmospheric characteristics, such as the proportion of sulphur dioxide in the atmosphere, are strongly influenced by these differences. This is particularly relevant when these properties are used to infer further knowledge about the physical and chemical processes within an atmosphere.

Furthermore, in his research project, Simon has focused on the assumptions underlying the models used to represent the atmospheres of exoplanets. Through a wide-ranging study, he has investigated the influence of the vertical temperature structure in exoplanet atmospheres. His research has shown that the simple assumption of an isothermal structure can significantly influence the results of atmospheric characterisation and lead to errors.

The latest results from the JWST and the expected observations from future missions, such as the Ariel space telescope, require us to further develop and closely scrutinise the methods we use to characterise the atmospheres of exoplanets. Simon is currently working on an application for the Erwin Schrödinger Fellowship, through which he aims to study entire populations of exoplanets and explore these topics further.

My time at the Department of Astrophysics has had a significant influence on my development as a researcher and as a person. My supervisors and VISESS have enabled me to engage in continuous exchange and professional development, not only within my research group but also within the broader research environment of VISESS and through international collaborations.