Laboratory Experiments and Numerical Models to Constrain Melt Migration Under Strike-Slip Faults on Europa

DESCRIPTION: The subsurface ocean on Jupiter’s moon Europa is encased in a geologically active icy shell. Strike-slip motion has been inferred on the double ridges of Europa (Hoppa et al., 2000), which produces tidally driven shear heating. This localized heating results in partial melt generation beneath the faults which may either form shallow water sills or the melt may instead drain through the ice shell and into the ocean. Although this process has been considered in previous studies (Kalousova et al., 2014; Craft et al., 2016), the relevant mechanical behaviors of partially molten ice at icy satellite conditions are largely unconstrained. Integrating results from ice friction experiments and shear heating models from my ongoing work studying the frictional behavior of icy satellite faults, I plan to conduct laboratory experiments to better constrain the permeability, capillarity, and effective bulk viscosity of partially molten ice with relevant impurities at icy satellite temperatures and use the experimental results as parameters for a numerical model of melt migration under strike-slip faults. The focus will be on Europa but the results are applicable to other icy satellites with strike-slip faulting (Cameron et al., 2018; Nimmo et al., 2007; Burkhard et al., 2022). This work will address:
1. What happens to melt generated by frictional heating at the double ridges on Europa?
2. Can shallow-water sills (“melt ponds”) form and remain stable under strike-slip faults?
3. Can melt migration transport oxidants (or other exogenic material) into the subsurface ocean?

The dynamics of melt in the ice shell may be relevant to both the exploration and habitability of icy satellites. Given the variable thickness of Europa’s ice shell (Billings and Kattenhorn 2005) and the challenges associated with it in exploring its ocean, the existence of a stable body of liquid water in the ice shell may make for a more realistic environment for future exploration. In searching for life, melt ponds may be their own potentially habitable niche, separate from the ocean on icy satellites. Closer to the surface, melt ponds would be more likely to contain radiolytically produced oxidants and exogenic material from the surrounding environment. The existence of stable melt ponds at geodynamic settings such as double ridges or chaos terrains would aid the selection of landing sites for future missions. If the melt instead drains through the ice, melt migration may then be a transport mechanism for material from the surface to the ocean. In particular, if radiolytically produced oxidants can make their way into the ocean, they may oxygenate the ocean in the absence of photosynthesis or direct ocean-atmospheric interaction, as is present on Earth (Chyba 2000). Therefore, melt migration could be a potential mechanism for oxidant supply into the ocean and we can better constrain this oxidant flux which would allow us to estimate the redox flux of Europa’s ocean and energy availability for life throughout its history. However, this is dependent on the oxidants reaching shallow subsurface melt. Oxidants may reach subsurface melt if they are penetrated further into the ice through impact gardening and/or plume deposition (Hand et al., 2006). Shear heating of ice with impurities involving deep eutectics may also allow for shallow melt generation. I am currently exploring the effect of partial melt and impurities on frictional fault behavior and hope to use the results to inform this proposed work.