How Does Salinity Shape Ocean Circulation and Ice Geom- Etry on Enceladus and Other Icy Satellites?
How does salinity shape ocean circulation and ice geom- etry on Enceladus and other icy satellites? Wanying Kang1∗, Tushar Mittal1, Suyash Bire1, Jean-Michel Campin1, and John Marshall1 1Earth, Atmospheric and Planetary Science Department, Massachusetts Institute of Technology, Cambridge, MA 02139, USA Of profound astrobiological interest is that not only does Enceladus have a water ocean, but it also appears to be salty, important for its likely habitability. Here, we investigate how salin- ity affects ocean dynamics and equilibrium ice shell geometry and use knowledge of ice shell geometry and tidal heating rates to help constrain ocean salinity. We show that the vertical overturning circulation of the ocean, driven from above by melting and freezing and the tem- perature dependence of the freezing point of water on pressure, has opposing signs at very low and very high salinities. In both cases, heat and freshwater converges toward the equa- tor, where the ice is thick, acting to homogenize thickness variations. In order to maintain observed ice thickness variations, ocean heat convergence should not overwhelm heat loss rates through the equatorial ice sheet. This can only happen when the ocean’s salinity has in- termediate values, order 20 psu. In this case polar-sinking driven by meridional temperature arXiv:2104.07008v2 [astro-ph.EP] 15 Apr 2021 variations is largely canceled by equatorial-sinking circulation driven by salinity variations and a consistent ocean circulation, ice shell geometry and tidal heating rate can be achieved. Since the Cassini and Galileo mission, Enceladus (a satellite of Saturn) and Europa (a satel- lite of Jupiter) have been revealed to have a high astrobiological potential, satisfying all three 1 necessary conditions for life: 1) the presence of liquid water 1, 2, 2) a source of energy 3, 4, and 3) a suitable mix of chemical elements 1, 5–10.
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