Self-Assembling Ice Membranes on Europa: Brinicle Properties, Field Examples, and Possible Energetic Systems in Icy Ocean Worlds

Brinicles are self-assembling tubular ice membrane structures, centimeters to meters in length, found beneath sea ice in the polar regions of Earth. We discuss how the properties of brinicles make them of possible importance for chemistry in cold environments-including that of life's emergence-and we consider their formation in icy ocean worlds. We argue that the non-ice composition of the ice on Europa and Enceladus will vary spatially due to thermodynamic and mechanical properties that serve to separate and fractionate brines and solid materials. The specifics of the composition and dynamics of both the ice and the ocean in these worlds remain poorly constrained. We demonstrate through calculations using FREZCHEM that sulfate likely fractionates out of accreting ice in Europa and Enceladus, and thus that an exogenous origin of sulfate observed on Europa's surface need not preclude additional endogenous sulfate in Europa's ocean. We suggest that, like hydrothermal vents on Earth, brinicles in icy ocean worlds constitute ideal places where ecosystems of organisms might be found.The authors thank Norm Sleep and two anonymous reviewers for helpful input, and Mohit Melwani Daswani for additional input on the nearly final manuscript. Brine calculations benefitted from work by JPL interns Nina Botha-my and Amira Elsenousy. S.D.V. thanks Bruce Bills and Baptiste Journaux for many stimulating discussions relevant to this work. Research by L.M.B. and S.D.V. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. L.M.B. and S.D.V. were supported by the NASA Astrobiology Institute (NAI) Icy Worlds project (13-NAI7-0024). S.S.S.C. acknowledges the financial support of the UK Leverhulme Trust project RPG-2015-002. J.H.E.C. acknowledges the Spanish MINECO grant FIS2016-77692-C2-2-P. No competing financial interests exist