Description du sujet de thèse

The CNRS and the University of Arizona are developing various scientific projects within a collaborative initiative entitled "In search of habitable worlds, in the solar system and beyond". One of these projects is called "Linking Cryovolcanism and Space weathering on Europa". It aims to link cryovolcanism and surface alteration by energetic particles ("space weathering") on the surface of Europa, icy satellite of Jupiter.

This project consists on the one hand in studying the potential transport mechanisms between the internal ocean of Europa and the surface and on the other hand in investigating the chemical evolution of the materials deposited by cryovolcanism on the surface of Europa, and in particular the fate of the organic species.

The first part, concerning the transport mechanisms, is conducted at the University of Arizona in Tucson. The second part is conducted concurrently in France at the Origins Institute of Aix-Marseille University, with the experimental part realized at the PIIM laboratory (UMR 7345 AMU CNRS), which is the topic of this thesis. It will be part of a PhD prepared at Aix-Marseille University. This PhD will be financed by a PhD contract. Thus, the selected person will be employed by the CNRS assigned to the PIIM laboratory for 3 years.

In the course of this part of the project, the PIIM will follow an experimental approach -irradiation of samples of analogous ice of the surface of Europe in vacuum chambers- to determine how the radiolytic processes make the surface evolve from the physicochemical point of view and how the nature of the ice (composition and structure) influences this evolution. During the thesis, the selected candidate will work on the evolution of the experimental design, the execution of the experiments and the interpretation of the resulting data.

The icy targets to be irradiated will include a water ice matrix and an organic compound of interest (i.e., alcohol, amine, carboxylic acid) with possible addition of compounds bringing other heteroatoms (nitrogen, sulfur). More complex compounds that could serve as bio-indicators (mixtures of amino acids) will also be considered. The experiments will be carried out in parallel at GANIL using an ion source. It will be possible to compare the reactivity induced by these different sources.

The refractory organic residue obtained at the end of the experiment (after sublimation of the most volatile compounds) will also be analyzed at our partners' facilities using Ultra-High Resolution Mass Spectrometry to determine the properties of the refractory material that could form on Europa's surface.

This work will notably allow to:

1) characterize the processing mechanisms of organic compounds in surface ice deposits on Europa;
2) characterize the reaction pathways and products made possible by the presence of sulfur and nitrogen;
3) determine the chemical (by gas chromatography and mass spectrometry), physical, and spectral (mid- and near-infrared) characteristics of organic products in the surface environment on Europa;
4) to provide results that will help the interpretation of data obtained by the JUICE and EUROPA CLIPPER space missions which have the common objective of studying Europa.

Publications related to the project:
• Tenelanda-Osorio, L., Bouquet, A. et al. (2022) Effect of the UV dose on the formation of complex organic molecules in astrophysical ices: irradiation of methanol ices at 20 K and 80 K. Monthly Notices of the Royal Astronomical Society, 515(4), 5009-5017
• Ruf, A., Bouquet, A., et al., (2021). “Sulfur ion irradiation experiments simulating space weathering of Solar System body surfaces-Organosulfur compound formation”. Astronomy & Astrophysics, 655, A74.
• Ruf, Bouquet, et al., “Organosulfur Compounds Formed by Sulfur Ion Bombardment of Astrophysical Ice Analogs: Implications for Moons, Comets, and Kuiper Belt Objects,” Astrophys. J. Lett., vol. 885, no. 2, p. L40, 2019.

Contexte de travail

The activity will take place on the university site of Saint-Jérôme in Marseille. The PIIM laboratory is classified in a restricted area (ZRR) which requires the attribution of a specific access authorization.

The person recruited will work within the research teams ASTRO (Astrochemistry, Spectroscopy, Theory, Reactivity, Origins) and H2M (Hydrogen, Molecules, Materials) at the PIIM laboratory, recognized for their experimental activities in astrochemistry, which combine classical vacuum techniques with cutting-edge analytical chemistry. All the numerical and experimental tools of the teams will be put at his disposal.

Part of the work will also be conducted at the Grand Accélérateur National d'Ions Lourds (GANIL) facility in Caen for sample preparation, and at the COBRA laboratory in Rouen for solid matter analysis by ultra-high resolution mass spectrometry. Travel to the United States to interact with the University of Arizona team is also expected; interactions with teams working on the most concerned space instruments (on the American Europa Clipper mission and the European JUICE mission) will also take place.

Frequent interactions with other laboratory of the Origins Institute will allow exchanges on topics related to the thesis subject (ongoing modeling of Jovian moons, space instruments…).

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

• Risk related to ionizing radiation,
• Laser risk,
• Chemical risk and the risk related to the handling of pressurized gas cylinders,
• Work on screens.

Informations complémentaires

Master's degree in analytical chemistry and/or physical chemistry is expected; experience with one of the above techniques and/or with a Ultra-high Vacuum system is a strong advantage. Knowledge of a computer language such as Python to assist in data analysis is also an important advantage. A background in planetology is appreciated.

Strong written and oral communication skills in English are expected. The ability to work in a team, autonomy, and initiative are also required.