In little more than two years of scientific operations, JWST has revolutionized our understanding of exoplanets and their atmospheres. The ARIEL space mission, to be launched in 2029, will soon contribute to this revolution. A main finding that has been enabled by the exquisite quality of the JWST data is that exoplanet atmospheres are in chemical disequilibrium. A full treatment of disequilibrium is complex, especially when the atmospheres are metal-rich, i.e. when they contain in significant abundances elements other than hydrogen and helium. In a first step, our project will numerically investigate the extent of chemical disequilibrium in the atmospheres of JWST targets suspected to have metal-rich atmospheres. We will use towards that end an in-house photochemical model. In a second step, our project will explore the effect of super-thermal chemistry as a driver of chemical disequilibrium. This will offer previously-unexplored insight into the chemistry of metal-rich atmospheres, with the potential to shed new light into the chemical and evolutionary paths of low-mass exoplanets.

Gamma-Ray Bursts are short lived (0.1-100 s) gamma-ray transient sources that appear randomly on the entire sky. Even if they have been discovered at the end of the 1960s, their nature remained mysterious until the end of the 1990s. It is only thanks to the observations of the BeppoSAX satellite at the end of the last century and especially thanks to the observations of the Swift satellite starting from 2004, that the mysterious nature of GRBs started to be elucidated.
These emissions are related to the final stages of very massive stars (30-50 times the mass of the Sun) for the long GRBs (<2 s) or to the merger of two compact objects (typically two neutron stars) for the short GRBs (< 2s). In either case there is the creation of a powerful relativistic jet, which is at the origin of the electromagnetic emission that is measure in gamma-rays and in other energy bands. If this jet points towards the Earth, GRBs can be detected up to very long distances (z~9.1) corresponding to a young age of the Universe (~500 Myr).
Svom is a sino-french space mission dedicated to GRBs, which has been successfully launched on June 22nd 2024, and in which CEA/Irfu/DAp is deeply involved. The PHD subject is aimed at exploiting the multi-wavelength data of SVOM and its partner telescopes in order to investigate the nature of GRBs, and in particular to make use of X-ray data from the MXT telescope in order to try to constrain the nature of the compact object which is at the origin of the relativistic jets.

Planet formation is a key topic of modern astrophysics with implications on existential questions such as the origin of life in the Universe. Quite surprisingly, we do not precisely know when and where planets are formed in protoplanetary disks. Recent observations however indicate that this might happen sooner than we previously believed. But the physical conditions in the young disks remain poorly constrained. During this thesis we propose to test the hypothesis that planets could form early. We will perform 3D simulations of protoplanetary disk formation with gas, dust and including the mechanisms of planetesimal formation. In addition from determining whether planets form early we will be able to predict the architectures of exoplanet systems and to compare them to real ones. This work, beyond the current state-of-the-art, is timely as many efforts are currently being done by our community to better understand exoplanets as well as our origins.