Constraining the planetary surface by detections of distinct atmospheric types of rocky exoplanet atmospheres

Future observations of rocky exoplanets are expected to enable the characterisation of their atmospheric compositions. This is expected to reveal a much larger diversity of atmospheric compositions than those known from our solar system. Although constraints on the abundances of atmospheric species might be possible, they will remain very challenging for rocky exoplanets. Therefore, the characterisation of exoplanetary atmospheres will rely on the theoretical understanding of potential atmospheric types and their observational differences. In addition to the implications on the atmosphere, these atmospheric types also function as a window into the surface conditions of the investigated planet.

During this presentation I will present our modelling approach on the connection between different atmospheric types, defined by their gas and cloud composition, and their corresponding surfaces. Our results are generated from a surface-atmosphere model which builds the atmosphere from bottom-to-top and includes cloud condensation.

Our investigations of various sets of elemental abundances based on different rock compositions reveal the diversity of atmospheric compositions, which form distinct atmospheric types. One of the most indicative links from the atmosphere to the surface conditions can be found in the chemistry of the sulphur species. While the sulphur cloud condensates of H₂S and H₂SO₄ only form for planets with high surface pressures and/or temperatures, the sulphur-bearing condensates at the planetary surface (including especially FeS, FeS₂, and CaSO₄) are directly linked to the atmospheric types. 

I will present model transmission spectra based on these atmospheric compositions, which show that the atmospheric composition can be constrained to a specific atmospheric type. Although it will remain challenging to obtain sufficient observations, these could in principle constrain the planetary surface mineralogy.