Experimental simulation of Enceladus’ hydrothermal vents to constrain the evolution of primordial organic matter with iron-rich saponite

Data from Cassini-Huygens on the plume composition, and by extension the supposed composition of the Enceladus ocean, revealed a variety of organic-bearing compounds in which no amino acids were identified [1]. Given that icy moons form from small primordial bodies [2], we wondered how the primitive organic matter containing amino acids [3,4] evolved once it was accreted. This is relevant considering how the complex matrix of organic matter, minerals, and ices might evolve during the interaction with hydrothermal water circulating through the porous core of Enceladus. Among the minerals composing the building blocks of the icy moons, saponite has been detected in asteroid Ryugu and carbonaceous chondrites [5], presenting catalytic properties and a crystallographic structure that might facilitate the polymerisation of prebiotic molecules such as amino acids [5, 6].

To investigate the potential catalytic role of saponite in prebiotic chemistry in Enceladus hydrothermal system, we recreated the hydrothermal conditions (150°C, 20MPa) in an internally heated pressure vessel, in which we reacted synthetic mixtures of Fe(II)-saponite [7] incorporating organic matter obtained from a mixture of formaldehyde and glycolaldehyde, and ammonium-bearing fluids [8]. We conducted in operando analyses of Raman and Infrared spectroscopy to identify the evolution of organic matter within the aqueous mixture.

These experiments are novel in that they explore the effect of the variation of proportions of the compounds (i.e., saponite, organic, water) on their co-evolution in hydrothermal conditions. We will discuss the presence and nature of organic molecules trapped within the saponite interlayers and their potential role in catalyzing prebiotic molecules during the formation of the Enceladus ocean and their impact on its habitability potential.

[1] Khawaja et al., 2025 (https://doi.org/10.1038/s41550-025-02655-y); [2] Reynard and Sotin, 2023 (https://doi.org/10.1016/j.epsl.2023.118172); [3] Pizzarello et al., 2010 (doi: 10.1101/cshperspect.a002105); [4] Potzili et al., 2023 (https://doi.org/10.3390/life13071448); [5] Viennet et al., 2023 (https://doi.org/10.7185/geochemlet.2307); [6] Viennet et al., 2022 (https://doi.org/10.1016/j.gca.2021.12.002); [7] Noda et al., 2021 (https://doi.org/10.3390/min11111244); [8] Kebukawa et al., 2020 (https://doi.org/10.1016/j.icarus.2020.113827).