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Dynamics of the global meridional ice flow of Europa’s icy shell

Nature Astronomy volume 2, pages 43–49 (2018)Cite this article

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Abstract

Europa is one of the most probable places in the solar system to find extra-terrestrial life1,2, motivating the study of its deep (~100 km) ocean3,4,5,6 and thick icy shell3,7,8,9,10,11. The chaotic terrain patterns on Europa’s surface12,13,14,15 have been associated with vertical convective motions within the ice8,10. Horizontal gradients of ice thickness16,17 are expected due to the large equator-to-pole gradient of surface temperature and can drive a global horizontal ice flow, yet such a flow and its observable implications have not been studied. We present a global ice flow model for Europa composed of warm, soft ice flowing beneath a cold brittle rigid ice crust3. The model is coupled to an underlying (diffusive) ocean and includes the effect of tidal heating and convection within the ice. We show that Europa’s ice can flow meridionally due to pressure gradients associated with equator-to-pole ice thickness differences, which can be up to a few km and can be reduced both by ice flow and due to ocean heat transport. The ice thickness and meridional flow direction depend on whether the ice convects or not; multiple (convecting and non-convecting) equilibria are found. Measurements of the ice thickness and surface temperature from future Europa missions18,19 can be used with our model to deduce whether Europa’s icy shell convects and to constrain the effectiveness of ocean heat transport.

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Fig. 1: Equilibrium state of the icy shell of Europa when the meridional ocean heat transport and ice convection are not included.
Fig. 2: Equilibrium state of the icy shell of Europa when ocean heat transport is included, while ice convection is absent.
Fig. 3: Equilibrium solutions when meridional ocean heat transport is absent and ice convection is active.
Fig. 4: Observational predictions and verification.

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Acknowledgements

E.T. was funded by the National Aeronautics and Space Administration Habitable Worlds programme (grant FP062796-A) and thanks the Weizmann Institute for its hospitality during parts of this work.

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Authors and Affiliations

  1. Department of Solar Energy and Environmental Physics, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel

    Yosef Ashkenazy & Roiy Sayag

  2. Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

    Eli Tziperman

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  1. Yosef Ashkenazy
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Y.A. and E.T. formulated the problem and performed the model runs and analyses. All authors contributed to the development of the model and the writing of the paper.

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Correspondence to Yosef Ashkenazy.

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Supplementary Figures 1–6, Supplementary Table 1, Supplementary References.

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Ashkenazy, Y., Sayag, R. & Tziperman, E. Dynamics of the global meridional ice flow of Europa’s icy shell. Nat Astron 2, 43–49 (2018). https://doi.org/10.1038/s41550-017-0326-7

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