The recent observations by the James Webb Space Telescop revealed a massive role of the out-of-equilibrium chemistry in temperate exoplanets, which cannot be explained with the simple models often implemented up to now. With the expertise of our group on out-of-equilibrium atmospheric chemistry, we were able to provide the best support to our community to tackle this challenge and to strongly contribute by investigating the importance of atmospheric chemistry in the field of exoplanets.
The work achieved during the first period of the project is threefold:
First we focused on temperate sub-Neptunes, as those are among the most promising exoplanets to be observed by the JWST and ARIEL in terms of habitability. Those are located close or in the habitable zone of their host star. Their atmosphere is hydrogen rich, and exhibits a high metallicity (a large amount of carbon in particular). Their proximity to their star involves an intense evaporation process leading to an efficient hydrogen loss toward the interplanetary medium, and a progressive enrichment in heavier molecules, like methane or carbon dioxide. Temperate sub-Neptunes are therefore to-date considered as key planets for studying how the secondary atmosphere of the early-Earth was formed. In order to investigate the gas-phase chemistry occurring in these exoplanetary atmospheres, we have therefore led a large range of experiments in H2 rich conditions, varying the content in methane vs carbon dioxide. The fine analysis of this large dataset is in progress, and major results are already revealed on the formation of oxydized organic molecules of interest for prebiotic chemistry.
Secondly, we tackled one of the main limitations for the interpretation of the exoplanets observations, which is the lack of knowledge on the optical properties of hazes. We synthesized experimentally a set of analogues of particles representative of various chemical conditions in exoplanetary atmospheres. Then we developed a demanding and rigorous methodology to characterize the particles’ optical properties on the broad UV-Far IR spectral, requiring measurements on multiple devices, among them IR measurements at SOLEIL, French national synchrotron facility. We were thus able to deliver during the first period of the project a pioneer work, providing the first optical properties of exoplanet’s haze in a large 0.3 to 30 μm spectral range, consistent with the JWST measurements.
Finally, another very important achievement concerns the experimental development of a specific reactor for investigating sulfur chemistry. Sulfur chemistry is indeed rather tricky to explore in the lab (corrosive and toxic). It has been therefore very few investigated in the past for planetary science. The chemical databases are poor by lack of experiments. Sulfur chemistry is however of prime importance in a number of planets, where volcanism is present. Our successful and safe experimental development therefore opens large perspectives for research in planetary science and atmospheric chemistry.
