The impact of salt on the microstructural and mechanical evolution of granular ice under Enceladus-like conditions

Icy moons such as Europa and Enceladus are known for their icy outer shells and liquid subsurface oceans that may be habitable [1,2,3]. Salt-bearing ice has been detected on their surfaces and is thought to have originated from these salty subsurface oceans. Sodium salts [4,5], and more recently phosphate salts [6], have been proposed as components of Enceladus’ surface and ocean. However, the effects of salt contamination on the surface evolution of icy moons under space-like conditions remain poorly constrained. We do not know how different salts influence the microstructural and mechanical evolution of icy moon surfaces. With ongoing and upcoming missions to icy worlds, it is important to have experimental analogue work to accompany the interpretation of data from these missions and help define mission design needs.

We experimentally investigate how salt contamination affects the microstructural and mechanical evolution of granular ice under Enceladus-like surface conditions. We prepare granular ice intra-mixtures of water and salts, and irradiate them in a pre-cooled vacuum chamber to examine how they evolve over time. The study includes monitoring temperature evolution during the simulation, pre- and post-exposure microstructural imaging and reflectance spectroscopy, and obtaining the depth-dependent mechanical strength profile of the samples after simulation. We found that surface evolution is highly dependent on salt type. All salt-bearing samples formed a crust, supported by their spectral changes and strength measurements, but had distinct depth-dependent strength profiles. Surface cracking was observed in some salt samples and appears to depend on salt type. This implies that salt-rich regions on icy moons may develop different mechanical properties and morphologies, depending on the dominant salt species present. Therefore, constraining salt type may be crucial for explaining surface evolution as well as for future lander missions, as near-surface consolidation and mechanical behavior seem to depend on salt type.

 

References:

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