From Buried Ocean to Surface Ice: Spectral Signatures of Leaking Oceans on Icy Moons.

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In our solar system, most of the oceans are covered by kilometers of ices. These buried oceans, considered amongst the most promising places to host extraterrestrial life, are now a priority in both ESA and NASA’s programs for in situ observations with landing missions. To prepare for these programs, and the scientific return of current/future missions, we need to understand how buried oceans interact with the surface, the paths to reach them, and whether we can know more about their composition and physical conditions before visiting them. In fact, while these oceans are buried under a crust of kilometers thick ice, they manage to leak to the surface and can be indirectly observed in several ways. Ocean water escape through geysers (plume) on the Saturnian moon Enceladus, subsurface fluids spill over onto the surface of the Gallilean moon Europa, or subsurface materials (ocean) lose some molecules that diffuse through the ice until reaching the surface where they are observed as ice. In parallel, James Webb Space Telescope (JWST) observations of the moons Ganymede and Europa have reported spectra showing subtle variations within the moon surface that are difficult to interpret but likely linked to the formation and evolution of surface ices. The aim of LeakingOceans is to determine the spectral signatures of ices produced by leaking oceans (plume, spilling or diffusion) allowing to identify these leaks in the observations. For this purpose, the processes by which buried oceans become surface ice will be studied experimentally and theoretically to obtain ices’ characteristics and spectral signatures. These tools will be instrumental for searching plumes on Europa or other moons. By determining signature and efficiency of the oceans’ leaks on icy moons, we will (1) understand the dynamics between oceans and surfaces of icy moons (2) deduce the composition and conditions present in these ocean worlds and (3) provide ways to reach these oceans for future exploration.