Enceladus and possibly Europa spew materials from their internal ocean into their exosphere, some of which are deposited back onto the surface of those Ocean Worlds. This setting provides a unique opportunity to seek traces of past or extant life in ice plume deposits on their surfaces. However, the design of lander missions and surface sampling techniques, and the choice of sampling locations rely heavily on strength expectations. Here we present an experimental investigation of the evolution in strength of ice plume deposit analogs at several temperatures, as well as a model that predicts first-order estimates of the strength of evolved ice plume deposits under geologic timescales relevant to Enceladus and Europa. These results suggest that plume deposits remain weak and poorly consolidated on Enceladus, while they may develop substantial strength (comparable to solid ice) within < 100 My on Europa.

Raman spectroscopy is a promising analytical technique for in situ characterization of the icy mineral context on the surfaces of Ocean Worlds. This technique is highly sensitive to the molecular environment of ice and non-ice constituents, whereby non-destructive measurements can be conducted without any specific sample preparation. However, the application of Raman spectroscopy for space exploration remains in its infancy. Potential in situ Ocean Worlds mission concepts seek a quantitative assessment of the icy mineralogical context of samples that would be further analyzed for organic content and possible traces of biosignatures, which could be satisfied with a Raman spectrometer. To begin assessing this possibility, the current study aims to evaluate how well a laboratory Raman instrument can quantify non-ice constituents in icy materials. Here, we focused on the binary H2O-Na2SO4 system because it is relevant to Europa, the materials that form upon freezing are well-understood, and the freezing behavior is predictable and devoid of metastable and/or glassy phases that could confound the analyses. We find that the sulfate-to-water peak area ratio shows a strong linear correlation with the salt concentration in the starting solution. Local heterogeneities in mineralogical abundances that likely developed during freezing of the solutions tend to degrade data precision and correspondingly increase the uncertainty of the estimated concentration from measurements conducted on frozen solutions. Future studies are needed to investigate other systems, include multiple components, and develop modeling approaches to account for textural and mineralogical variability in icy materials. Part of this work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Copyright 2021. All rights reserved.