Abstract
Ocean worlds have been identified as high-priority astrobiology targets
due to the link between life and liquid water. Young surface terrain on
many icy bodies indicates they support active geophysical cycles that
may facilitate ocean-surface transport that could provide observables
for upcoming missions. Accurately interpreting spacecraft observations
requires constraining the relationship between ice shell characteristics
and interior dynamics. On Earth, the composition, physical
characteristics, and bioburden of ocean-derived ices are related to
their formation history and parent fluid composition. In such systems
the ice-ocean interface, which exists as a multiphase mushy layer,
dictates the overlying ice’s properties and evolution. Inclusion of the
physics governing these boundaries is a novel strategy in modeling
planetary ices, and thus far has been limited to 1D approaches. Here we
present results from 2D simulations of an archetypal ice-ocean world. We
track the evolution of temperature, salinity, porosity, and brine
velocity within a thickening ice shell enabling us to place improved
constraints on ice-ocean world properties, including: the composition of
planetary ice shells, the thickness and hydraulic connectivity of
ice-ocean interfaces, and heterogeneous dynamics/structures in the
interfacial mushy layer. We show that stable eutectic horizons are
likely a common feature of ice-ocean worlds and that ocean composition
plays an important role in governing the structure and dynamics of the
interface, including the formation of chemical gradient-rich regions
within the mushy layer. We discuss the geophysical and astrobiological
implications of our results and highlight how they can be validated by
instrument specific measurements.