What is the Thickness of Europa’s Water–ice Shell

Constraining the thickness of Europa’s water–ice shell: Insights from tidal dissipation and conductive cooling

Authors:

Quick et al

Abstract:

The time of crystallization of a 100 km thick ocean on Europa is estimated using a Stefan-style solidification solution. This solution is then extended to estimate the present thickness of the ice shell. It is assumed that the shell is initially in a steady-state conductive regime, and the ocean is taken to be an infinite liquid half space cooling from above. We find that in the absence of tidal heating and without the presence of low-eutectic impurities to serve as anti-freezes, a 100 km thick ocean solidifies in about 64 Myr. Conversely, when considering the present thickness of Europa’s ice shell, if tidal heating is included at a global dissipation rate of ∼1 TW, the shell is found to be, on average, approximately 28 km thick. However, if this dissipative heating is solely restricted to the shell, the local rate of heating may vary significantly due to crustal compositional heterogeneities and it is shown that this process may, in turn, produce thermal maxima in the crust, which could lead to local melting and structural instabilities, perhaps associated with the formation of chaos regions. Our approach is also extended to Ganymede and Callisto in order to estimate the time of solidification of their putative subsurface oceans and the current thicknesses of their ice-I shells.