24-188 High Temperature Cross-section Measurements

il y a 3 semaines


Paris, France CNES - Centre National d'Etudes Spatiales Temps plein

Doctorat, 36 mois
- Temps plein
- Aucune expérience exigée
- Maitrise, IEP, IUP, Bac+4
- Exobiology, Planetary protection & Exoplanets

**Mission**:
As shown by the first observations of the JWST (James Webb Space Telescope), the next generation of space missions (JWST but also ARIEL, Atmospheric Remote-Sensing Infrared Exoplanet Large-Survey) will allow major advances in the knowledge of planetary systems through the study of exoplanets. Less than thirty years ago, the discovery of the first exoplanets revealed the diversity of planetary worlds that exists in the Universe. Since then, several thousand of exoplanets have been confirmed with very various masses, radius, and orbital parameters. Spectroscopic observations performed these last years using the space-based telescopes Hubble and Spitzer and ground-based instruments permitted to characterize the presence of a few molecules in the atmosphere of exoplanets and also to constrain the thermal structure of these latters. However, the quality and the quantity of current observations make that many unknowns remain concerning these worlds: what are the links between the nature of the star and the characteristics of the planets? How is the chemical composition of the atmosphere and its evolution related to the training environment? Since a little more than one year now, JWST provides very good quality observations, with a very large spectral coverage, allowing the first detection of key molecules such as CO2 and SO2. However, to improve deeply our knowledge of exoplanetary worlds, and answer the questions listed above, the systematic study of a very large number of planetary systems is mandatory. This large-scale study will be carried out by the ESA-M4 mission ARIEL (PI: G.Tinetti), which will be launched in 2029. We are strongly involved in this mission since Olivia Venot is a member of the Scientific Consortium, head of the "Chemistry" Working Group, and member of the ESA Science Team. In addition, we are also very involved in the analysis of JWST observations.

The chemical composition of exoplanets will be determined by comparing the observations of the telescopes ARIEL and JWST with the results of different models: kinetic model and retrieval model. The confidence index in the interpretation of observations therefore depends essentially on the reliability and robustness of the models used. For this thesis, we propose to focus on the improvement of photo-thermochemical models used to determine the chemical composition of exoplanets. This is an essential step to improve the understanding of the chemical composition of exoplanet atmospheres from future observations of these telescopes.

A major source of uncertainty in photo-thermochemical models is the inadequacy between the physico-chemical data used (mainly the absorption cross sections known at ambient temperature) and the characteristics of the atmospheres studied (very high temperatures). To correctly represent the chemical composition of hot exoplanets, we want to experimentally determine the thermal dependency of the VUV absorption cross sections for the main molecules of atmospheric interest. These data are almost inexistent and are eagerly awaited by the community. The team "Exobiology and Astrochemistry" of the LISA is one of the few in the world to have the expertise to carry out these determinations and has already gained international recognition in this field. In the recent years, we have studied the cross-sections (and thermal dependency) of CO2 (Venot+2013, 2018), CO (Poveda+in prep), and C2H2 (Fleury, Poveda+in prep). These measurements have been performed on our new spectroscopic platform installed at LISA, whose deployment was made possible thanks to the support of the CNES (APR EXACT & PhD funding of Mathilde Poveda). Our results show the important dependency with temperature of these data, and the impact on the atmospheric composition of exoplanets.

Given the quality of JWST and future ARIEL observations, it is mandatory to use absorption cross sections adapted to the conditions of warm exoplanets, which are the main targets of these telescopes. This thesis will exploit the instrument (VUV spectroscopic platform) deployed thanks to the CNES in order to measure the absorption cross-section of important species for planetary atmospheres. We have already identified our next target species, NH3, SO2 and HCN, which will be studied in the context of this thesis.

=================

**Profil**:
Owner of an astrophysical or molecular physics Master, the student will have a good knowledge of molecular physics and will be attracted by experimental sciences.

**Infos pratiques**:
LISA

**MESSAGE from Phd Team**:


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