Thesis defense “Evolution of primordial organic matter in ice satellites and dwarf planets: an experimental approach” – Pauline Lévêque

Recent studies suggest that the interiors of ice moons and dwarf planets are composed of silicates, sulfides, ices and organic matter (OM). During the differentiation of the hydrosphere of these icy bodies, primordial organic matter was altered by contact with liquid water. Determining and
characterizing the reaction products of this OM is necessary to understand its influence on the thermochemical evolution of icy bodies. Experiments were carried out to reproduce these alteration conditions (P<5 GPa, T<400°C), on analogous samples synthesized at the CRPG laboratory. The N/C ratio of these samples varied (N/C < 0.63) to reflect the diversity of the primordial OM. Highresolution FT-ICR mass spectrometry measurements show that these samples are good analogues of the OM of the solar system’s most primitive bodies. Their aqueous alteration shows their evolution towards highly condensed polycyclic aromatic hydrocarbons (PAHs). The volatile products of this degradation were identified by gas chromatography, Raman spectroscopy and X-ray diffraction.
From 200°C, CO2 and N2 are released, then CH4 appears in addition at 400°C. The abundance of CO2 allows carbonates to precipitate as early as 200°C. Denser than the ocean, PAHs and carbonates should mix with silicates and sulfides to form a refractory core that evolves as temperature rises. These experiments provide potential explanations for the presence of N2 and CH4 in Titan’s atmosphere, and for the carbon-rich regions observed on the surfaces of Ceres, Europa
and Ganymede.

Location : Faculty of Sciences, Nantes University