Compositional heterogeneities in the outer ice shell of Europa – a scale-coupled computational study

• Applicants: Professorin Dr. Julia Kowalski; Dr. Ana-Catalina Plesa
• Subject Area: Geophysics ; Astrophysics and Astronomy
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 460819306

Studying the icy moons of the Jupiter and Saturn system is highly desired by the scientific community, as it will a) improve our understanding of the solar system’s evolution, and b) yield insight into these moon’s potential to harbor life outside Earth. The presence of liquid water oceans in their interior, which may be in contact with the silicate core (e.g., Europa) makes these worlds ideal candidates for the search of habitable environments. The present-day surfaces and interiors of icy satellites are a result of evolutionary processes. Of particular interest is the evolution of the outer ice shell, which is in direct contact with the subsurface ocean. Chemical composition (salt impurities) in the ice shell is subject to change due to reactive interface processes at ice-water interface, e.g. at the ice-ocean boundary or within crack systems of tectonic or cryo-volcanic origin. At the same time, the outer ice affects both the morphology of the surface, and the composition of the liquid ocean by material transport through solid-state convection. While compositional heterogeneities have been observed at the surfaces of e.g., Ganymede, Europa and Callisto by the Galileo Near-Infrared Mapping Spectrometer (NIMS), little is known about chemical anomalies in the subsurface. These heterogeneities may lead to formation of liquid pockets, which, if stable over longer time periods, constitute potential near-surface habitable environments. The Jovian moon Europa is a particularly interesting candidate for subsurface habitability in the outer Solar System. Future measurements of the ESA’s JUICE mission and NASA's Europa Clipper mission scheduled for launch in 2022 and 2024, respectively, will analyze the composition of non-water ice material at Europa's surface. Investigation of recently active surface regions will help understand the interaction between the surface, ice shell and ocean, while additional measurements will constrain the thickness of the icy shell, the degree of heterogeneity and presence of liquid pockets in the outer ice shell. A better understanding of both origin and evolution of chemical heterogeneities in the outer ice shell of Europa is therefore necessary to provide a reliable interpretation of forthcoming space mission data.Our major goal for this project is to develop a hybrid, scale-coupled numerical modeling approach that combines a computational mesoscale model of the ice-ocean boundary layer with macroscale models of solid-state convection, and to apply it in order to improve our understanding of mixing efficiency and distribution of chemical anomalies in the outer ice shell. In this project, we will focus on Europa’s icy shell. Nevertheless, we emphasize that the proposed computational strategy is generic and it is our plan to extend our studies to other Jovian and Saturnian moons in the future.

• DFG Programme: Research Grants