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Fate of primitive organic matter during icy moons’ geological evolution

Presentation #114.03 in the session Laboratory Investigations (Oral Presentation)

Published onOct 23, 2023
Fate of primitive organic matter during icy moons’ geological evolution

Organic molecules are ubiquitous in primitive solar system bodies such as comets and could be a major component of the icy moons, and dwarf planets [1]. Primitive organic molecules (OM) may have formed in the interstellar medium (ISM) and in the protoplanetary disk (PPD) before being accreted in the building blocks of larger outer solar system objects. During the early differentiation of large icy moons, like Ganymede and Titan, this primitive OM would have been exposed to large amounts of liquid water at pressures of several GPa and temperatures up to a few tens of degrees above the ice melting point [2]. The evolution of the OM at these conditions remains largely unknown. We have studied the evolution of primitive organic matter analogues produced in a laboratory simulator of the protoplanetary disk (aka Nebulotron). The amount of nitrogen varies from N/C(bulk)=0 to N/C(bulk)=0.63. The initial organic matter has been analyzed using FT-ICR-MS. Highly condensed polyaromatic (PAHs) molecules were observed in every sample. High nitrogen content leads to a dramatic increase of the chemical diversity dominated by N-bearing molecules composed of 5- to 6- membered rings containing up to 4 nitrogen atoms. Evolution of the organic matter analogues with water at conditions relevant to the interior of large icy moons during its differentiation (<7 GPa, Tmax=700 K) was observed in diamond anvil cells. In situ Raman spectroscopy and single-crystal X-ray Diffraction provide information on 1) the chemical species released during the reactions of the OM in presence of water, and 2) the amount of graphitization of the organic matter. Carbonates appear as the major species formed during our experiments. No crystalline carbon phase (e.g. graphite or diamond) was detected. Nitrogen rich analogs are highly reactive in the hydrolysis process. These results suggest that, just after the differentiation into a hydrosphere and a refractory core, Ganymede and Titan’s refractory cores would be composed of hydrated silicates, carbonates, and highly condensed organic matter. References: [1] Reynard B. & C. Sotin, Earth Planet Sci Lett,612; 2023 [2] A. Néri, et al, Earth Planet Sci Lett, 530; 2020.

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