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Sensing the Endgame for Callisto's Ocean
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  • Steven Vance,
  • J. Michael Brown,
  • Bruce Bills,
  • Christophe Sotin,
  • Baptiste Journaux,
  • Krista Soderlund
Steven Vance
Jet Propulsion Laboratory, California Institute of Technology

Corresponding Author:[email protected]

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J. Michael Brown
university of washington
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Bruce Bills
Jet Propulsion Laboratory, California Institute of Technology
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Christophe Sotin
Jet Propulsion Laboratory, California Institute of Technology
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Baptiste Journaux
University of Washington
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Krista Soderlund
University of Texas at Austin
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We explore the possibility that Callisto’s ocean sits beneath its high-pressure ice, rather than above it. Oceans perched between ice phases are considered to be stable configurations for Ganymede, Callisto, and Titan. High-pressure ices under the liquid water ocean will transport heat and solutes into the ocean as long as the convective adiabat for the ices remains close to the melting temperature (Choblet et al. 2017, Kalousova and Sotin 2018). However, this configuration may become unstable when the perched ocean is close to freezing and its salinity increases, if the ocean becomes denser than the underlying ice. Among the oceans in the solar system, Callisto’s must be among the coldest and most saline because the internal heat appears to be low in the absence of tidal dissipation. Surface geology indicates its lithosphere is fully stagnant (Moore et al. 2004). Solid-state convection may continue beneath less than 100 km or dirty non-convecting ice (McKinnon 2006). And just below this layer may reside a liquid water ocean that is the lag deposit of Callisto’s thicker primordial ocean, the concentrated result of 4 Gyr of freezing. Using representative interior structures based on the current constraints from the Galileo mission (Anderson et al. 2001) coupled with recently obtained thermodynamic data (Vance et al. 2018), we demonstrate the possibility for using magnetic induction to identify where the ocean currently resides in Callisto. Anderson, J. D. et al. (2001). Shape, mean radius, gravity field, and interior structure of Callisto. Icarus, 153(1):157–161. Choblet, G. et al. (2017). Heat transport in the high-pressure ice mantle of large icy moons. Icarus, 285:252–262. Kalousovà, K. and Sotin, C. (2018). Melting in high-pressure ice layers of large ocean worlds - implications for volatiles transport. Geophysical Research Letters. McKinnon, W. (2006). On convection in ice I shells of outer solar system bodies, with detailed application to Callisto. Icarus, 183(2):435–450. Moore, et al. (2004). Callisto. Jupiter. The Planet, Satellites and Magnetosphere, 1:397–426. Moore, J. and Pappalardo, R. (2011). Titan: An exogenic world? Icarus, 212:790–806. Vance, S. D. et al. (2018). Geophysical investigations of habitability in ice-covered ocean worlds. Journal of Geophysical Research: Planets, 123, 180–205.