Through the Looking Glass: Understanding Planetary Oceans through their Ice Shells

Without direct access to their oceans, exploration of Ocean Worlds beyond Earth heavily relies on understanding the ice shells that separate these oceans from the surface. Planetary ice shells possess some unique processes, but also represent the exotic manifestation of processes familiar to us on Earth. The geodynamic evolution of an ice shell is also directly coupled to the history of the planet and its ocean, and geophysical techniques are a frontier in exploring these worlds. Thus there are many opportunities where terrestrial analogs play an important role in our understanding of planetary oceans, particularly at the poles. The ice shells of the outer solar system are derived from freezing and exchange with underlying oceans, which is expressed at the surfaces of these worlds in varying ways from global tectonic expansion observed in small worlds where oceans have cooled, to disrupted and potentially subducted ice that together reflect exchange of material between the surface and the subsurface. In this regard, oceans on these worlds are both oceans similar to the Earth's--likely rich in salts, having global dynamics and interacting with the seafloor in a variety of ways, and also play roles similar to Earth's mantle--sourcing material for the ice shell and potentially driving thermal exchange with the shell. This means that the ocean and the ice shell are physically and chemically linked, and that surface composition and geologic processes provide windows into ocean characteristics and processes. As a result, geophysical sensing of these ice shells help us to understand their oceans. We will highlight the upcoming observations to be made by the Europa Clipper spacecraft, including ice penetrating radar, topographic analyses and potential fields (gravity and magnetics) as well as future opportunities with landed seismic and electromagnetic techniques to explore the ice and ocean together. We will also discuss progress that can be made through interactions with the ocean science community and work on terrestrial analogs.