¹Olivier Poch et al. (>10)
Science 367, eaaw7462 Link to Article [DOI: 10.1126/science.aaw7462]
¹Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38000 Grenoble, France.

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¹Mario Fischer-Gödde,¹Bo-Magnus Elfers,¹Carsten Münker,²Kristoffer Szilas,³Wolfgang D. Maier,¹Nils Messling,^4,5,6Tomoaki Morishita,⁷Martin Van Kranendonk,⁸Hugh Smithies
Nature 579, 240-244 Link to Article [DOIhttps://doi.org/10.1038/s41586-020-2069-3]
¹Institut für Geologie und Mineralogie, University of Cologne, Cologne, Germany
²Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark
³School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK
⁴Faculty of Geosciences and Civil Engineering, Institute of Science and Engineering, Kanazawa University, Kanazawa, Japan
⁵Lamont-Doherty Earth Observatory, Columbia University, New York, NY, USA
⁶Volcanoes and Earth’s Interior Research Center, Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
⁷Australian Centre for Astrobiology, University of New South Wales, Sydney, New South Wales, Australia
⁸Geological Survey of Western Australia, East Perth, Western Australia, Australia

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^1,2Tuan H.Vu,^1,2Mathieu Choukroun,^1,2Robert Hodyss,^1,2Paul V.Johnson
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113746]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
²NASA Astrobiology Institute, USA
Copyright Elsevier

The composition of Europa’s subsurface ocean is of great interest for understanding the internal geochemistry and potential habitability of this icy body. However, current constraints on the ocean composition need to rely largely on its expression on the surface. In this work, we combine chemical divide modeling with cryogenic Raman and X-ray diffraction experiments to examine freezing of a simple putative brine system containing Na⁺, Mg²⁺, Cl⁻, and SO₄²⁻ across a range of ionic concentrations and freezing rates to assess the feasibility of inferring the ocean’s chemical composition via in-situ techniques. The results suggest that multiple hydrated salts not predicted by chemical models are frequently encountered in the final solid phase, making accurate quantification of the subsurface liquid composition via surface observables rather challenging. In addition, flash freezing of diluted brines often produces water ice together with amorphous hydrated Mg salts, which may significantly hinder their detection. These findings can help inform both analytical protocols for a Raman spectrometer onboard a Europa surface lander as well as potential locations for exploration, in order to best provide meaningful constraints on emplacement mechanisms and the composition of frozen salt minerals on the surface.