Ice-Ocean interactions and the circulation of salty oceans on Icy Moons

The potential for life is considerably increased in the presence of liquid water, an energy source, and nutrients. There is growing evidence that some of the Icy moons of the solar system (e.g., Europa) harbor liquid oceans, putting them at the forefront of the search for extra-terrestrial life. But it remains unclear whether these oceans are salty, that is, contain potential nutrients useful for life.

From a dynamical point of view, a salty ocean is expected to behave in a very differently to a freshwater ocean. This is in part due to the non-linearities of the equation of state for salty water (notably cabelling and thermobaricity). In the case of a subglacial ocean, transports of heat and freshwater/salt are also tightly coupled because of processes at the ice-ocean interface, some of which are strongly salinity-dependent (e.g., freezing point).

The working hypothesis of this project is that the differences in ocean circulation due to salinity could be observable through signatures on the outer ice shell and the magnetic field, giving us a probe into the chemical composition of oceans of Icy moons and one of the conditions for life. This PhD project is a first step in this direction by addressing the following objectives:

1. Clarify and quantify the differences in circulation between salty and freshwater oceans, 2. Determine potential signatures of these circulations on the ice shell (e.g., rates/pattern of ice renewal)

Few studies have addressed the 3-dimensional ocean circulation of the Icy moons. None has explicitly accounted for the ocean-ice interaction and a realistic representation of the coupled heat/water/salt fluxes at the ocean-ice interface. As a result, effects of salt on the 3D ocean state have not been addressed.

On a shorter term than that required to evaluate the habitability of the icy moons, the present work is a step change in understanding the dynamics and evolution of these moons, eventually feeding into missions such as the ESA's Jupiter Icy Moons Explorer JUICE.

The approach will combine numerical modelling with a state-of-the-art General Circulation Model and idealized theoretical models of the ocean.