PhD Defense: Alizée Amsler

Members of the jury :

• Christophe SOTIN (Nantes Université) – Reviewer
• François LEBLANC (LATMOS, Paris) – Reviewer
• Emmanuel LELLOUCH (LIRA, Observatoire de Paris) – President
• Vincent HUE (LAM, AMU) – Examiner
• Frank POSTBERG (Freie Universität Berlin) – Examiner
• Audrey VORBURGER (Bern University) – Examiner
• Olivier MOUSIS (LAM, AMU) – Supervisor
• Alexis BOUQUET (PIIM, AMU) – Co-supervisor

Abstract :

Since Galileo discovered the first icy moons in 1610, these bodies have continued to raise questions about their current composition, formation process, and evolution. Numerous observations and measurements made in recent decades using telescopes and space missions have revealed the many unique and sometimes unexpected characteristics of these ice moons. Among these bodies, Europa, Ganymede, Callisto, Titan, and Enceladus are of particular interest due to their specific characteristics, but also because of the potential presence of an ocean beneath their icy crust. The presence of such an ocean raises the question of their possible habitability, especially for Europa and Enceladus, whose oceans are in contact with their rocky mantles. Jupiter’s system will be intensively explored over the next decade by the ESA/JUICE and NASA/Europa Clipper missions, launched in 2023 and 2024 respectively. The future data acquired by these missions will enable a major leap forward in our understanding of their formation conditions and potential habitability. However, this will only be possible if these data are correctly interpreted in terms of the physical and chemical processes that occurred during the moons’ evolution.

In this context, this thesis aims to evaluate how the processes that occurred after accretion, affected the nature and distribution of volatile species present in the hydrosphere of icy moons. It focuses more specifically on the earliest phase of the moons’ existence, known as the “open ocean” phase, which precedes the formation of the ice crust above the ocean. In order to model the evolution of the composition of the primordial hydrosphere of the icy moons, three processes are taken into account: the equilibrium between the ocean and the primordial atmosphere, the formation of clathrates, and water-rock interactions. Two studies were conducted during this thesis. The first one focuses on Europa and the influence of the abundance of different accreted volatiles on the composition of its primordial hydrosphere. The second focuses on Titan and examines how clathrate formation during its primordial phase could explain the absence of noble gases in its current atmosphere.

The results of this thesis aim to provide key information to facilitate the interpretation of data from future Europa Clipper and JUICE missions, particularly with regard to the composition of the ocean. These measurements, expected in particular from the JUICE/NIM and Clipper/MASPEX mass spectrometers, will provide greater insight into the scenarios for Europa’s formation and the key processes involved in its evolution.