Atmospheres of exoplanets are our main observing window into the physical and chemical properties of these remote worlds. Hot exoplanets found very close to their stars have been found to lose a substantial fraction of their atmospheres. It is surmised that such planets could be entirely stripped of their atmospheres, raising the possibility that gaseous planets in milder irradiation regimes could give birth to smaller planets with residual, Earth-like atmospheres.
Upper atmospheres give rise to spectacular spectroscopic signatures in the UV (H) and more recently in the IR (He). Observations of exospheres in the UV only yield part of the information about the escaping gas which need to be completed by probing the thermosphere in the IR. It is thus essential to simulate self-consistently thermosphere and exosphere. The joint interpretation can be done using sophisticated simulations with the EVaporating Exoplanets (EVE) code. The main purpose of the EVE code is to calculate the absorption of stellar light across the simulated atmosphere. The better coupling of thermospheric and exospheric structure allows us to interpret together observations of upper atmospheres obtained in the UV and near-IR.
In addition, synergies between chemical models and chemical experiences will help understand the chemistry in the remaining Earth-like atmospheres. Because sulfur may play a crucial role in prebiotic chemistry and now that it has been observed in exoplanets (SO2 in WASP-39b), our goal is to improve the understanding of sulfur chemistry in exo-Earth atmospheres. Experimenting with sulfur under a wide range of oxidation and reduction conditions aims to discover the reactivity that can occur. It will be done by analyzing reactor synthesized products, identifying new chemical pathways, and checking with chemical models.