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The surface of some of the Jovian and Saturnian moons for which subsurface oceans have been proposed contains materials denser than water like rock. What keeps the surface from sinking under the subsurface ocean?

Also, what is the explanation for ruling out a process of differentiation during the moons' formation that placed material denser than water on top of subsurface oceans?

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    $\begingroup$ Source of claim? $\endgroup$ Apr 10, 2023 at 1:12
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    $\begingroup$ I'm not convinced by your claim that the surface contains materials denser than water. Do you have a source for this information? As far as I know, the surface is ice, which explains why it doesn't sink. $\endgroup$
    – Jim421616
    Apr 10, 2023 at 4:14

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What is the source of the claim? Let's take Enceladus as it is believed to contain subsurface ocean. Enceladus is mostly ice making it the most reflective body in the Solar System and since it reflects most of the sunlight, the temperature at surface level only reaches a mean noon temperature of −198 °C. Thus, most of the ice always stays frozen. Since ice is less denser than the water, it stays afloat. Also note that the subsurface ocean contains salt. Observations with Cassini revealed that the icy crust is thinner at the poles and thicker at the equator because the ice at the poles might be melting while the ice at the equator is freezing. As the ice melts and freezes, it changes the local concentration of salt i.e. when salty water freezes, the salt gets left behind, causing any remaining water to become heavier and that heavy water sinks in that region, and rises where the ice melts.

References

  1. https://www.universetoday.com/150749/there-are-ocean-currents-under-the-ice-on-enceladus/
  2. https://www.calacademy.org/explore-science/enceladen-oceans
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