Double-diffusive convection in Europa's icy shell and subsurface ocean

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Europa, a mid-sized satellite of Jupiter, is a unique icy body which shows a remarkable variety of features, indicating a young surface and widespread activity. Magnetic field data from the Galileo spacecraft and the images of potentially erupting plumes from the Hubble Space Telescope provided compelling evidence for the presence of a subsurface ocean. Colored bands and disrupted terrains on the surface are enhanced in hydrated minerals, potentially indicative of the composition of the subsurface ocean. These observations invoke various hypotheses of how materials are being transported from the seafloor to the surface by hydrothermal plumes, and raises questions on heat transfer. Here we propose to investigate double-diffusive convection, the process in which both the temperature and composition (or salinity if the chemical constituent is salt) are involved the dynamics of the convecting layer, therefore having significant consequences on the thermal evolution of Europa which we aim to understand. Chemical heterogeneity affects the vigour of convection, the forms of plumes, the generation and destruction of stratified or finger structures in the ocean, and thus the transport of heat and materials from the interior to the surface. We will model convection in the icy shell and the subsurface ocean first as separate systems to study their behavior as a function of theirproperties. After establishing a basic understanding of each system, we will examine their coupled evolution to see how the dynamics in one system affect the other. A number of numerical codes (finite volume, finite element, spectral methods) are available to study the icy shell (infinite Prandtl number) and the ocean (low Prandtl number). The results will enable us to (1) constrain the depth of the icy shell, (2) estimate the timescale of mixing, (3) infer the heat flux, and (4) provide clues about the formation of surface features. The approach developed in this research will be pertinent to studying icy bodies harbouring subsurface oceans, which are prospective destinations for future exploration. The predictions from this study can be tested by expected observations from the upcoming ESA JUICE and NASA Europa Clipper missions. This will further our knowledge on the physical processes and the evolution of Europa, having important implications for the satellite's evolution, surface environment, and habitability.