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Chemical EXchanges On WATER-rich worlds: Experimentation and numerical modelling

Final Report Summary - EXOWATER (Chemical EXchanges On WATER-rich worlds: Experimentation and numerical modelling)

The main goal of the EXOWATER project was to characterize the chemical exchanges within water-rich bodies including icy moons of the giant planets and dwarf planets in the Solar System, as well as exoplanets that are now discovered around other stars. Recent spacecraft missions, Galileo (1996-2003) and Cassini-Huygens (2004-today), have revealed that complex chemical exchanges occur between their warm silicate inner core and the water-rich outer layer on Jupiter's moon Europa and Saturn's moons Enceladus and Titan. Similar exchange processes are also likely to occur within water-rich planets outside our Solar System. By combining experimental investigations and numerical modelling, we investigated the possible interaction between seafloors, oceans, ice shells, and surfaces, atmospheres of water-rich worlds. This original approach allow us to quantify the efficiency of chemical exchanges between the internal layers composing these water-rich worlds and the consequences on their thermo-chemical evolution, which is necessary first step to assess their astrobiological potential.

More specifically, we investigated experimentally the stability of volatile compounds such as CO2, CH4, N2 in water-rich interiors and surfaces, with particular applications to Titan and Ganymede. These new experimental data provide fundamental constraints on the chemical evolution of their interiors and the role of internal volatile transport and outgassing for the generation of an atmosphere. For Titan, we showed by analyzing Cassini-Huygens data that Titan likely harbors a salted ocean underneath a cold and conductive ice layer, suggesting reduced chemical exchange with the surface at present. However, we showed by modeling the early stage of its evolution that intense chemical exchanges between the internal ocean, the crust and atmosphere occurred until at least the Late Heavy Bombardment epoch. For Enceladus, using full 3D models of tidal deformation developed during the project, we showed that tidal processes control the surprising activity observed at Enceladus’ south pole by Cassini and favored chemical exchanges between the rock core, the ocean and the surface. We also developed two-phase flow models of water and ice mixture in order to determine the conditions under which intense tidal heating may generate meltwater reservoirs at shallow depths on Europa, which may be detected by future ESA and NASA exploration missions. Finally, we developed a generic model to quantify the tidal response of exoplanets with various H2O content and the impact of tidal heating on their thermal state, which is essential to assess the impact of tides on their planetary habitability.