Tidally heated convection: Constraints on Europa's ice shell thickness

Abstract

[1] The thickness of Europa's ice shell is constrained with numerical experiments of thermal convection, including heterogeneous tidal heating. Thermal convection occurs in the stagnant lid regime with most of the tidal heating located in the bottom half of the layer. The addition of tidal heating mainly results in the increase of the temperature of the well-mixed interior and in the decrease of the heat flux at the base of the ice layer. In many simulations, the ice in hot plumes is heated up to its melting point. This induces episodic upwellings (0.5 Ma) of partially molten ice up to the base of the conductive lid, with possible implications for the formation of lenticulae and chaos regions. The thickness of the convective ice shell in equilibrium with the heat flow from the silicate core is estimated to be about 20-25 km. Tidal dissipation and surface temperature variations create lateral variations of the ice shell thickness of about 5 km, with maxima near the equator at the Jovian and anti-Jovian points and minima at midlatitudes. Surface heat flux is about 35-40 mW.m À2; it is almost constant all over Europa's surface, even though the tidal dissipation rate is four times larger at the poles than at the equator.

Resorption process in Astypalaea Linea extensive region (Europa)

“…However, jovian tidal heat dissipation may preserve a liquid water ocean under the icy crust and allow internal dynamics (e.g. Ojakangas and Stevenson, 1989;McKinnon, 1999;Ruiz and Tejero, 2003;Tobie et al, 2003). The small impact crater density commonly implies a young mean surface age ranging from 30 to 70 Myr (Zahnle et al, 2003) and then a resurfacing rate similar to those of the Earth's oceanic crust.…”

Tectonic history of Europa: Coupling between internal evolution and surface stresses

“…Consequently, tidal heating in the whole ice shell is small, and its volumetric rate is less than the radiogenic heating rate in the core by roughly an order of magnitude. In this work, the amplitude of tidal deformation is assumed to be about 16 m, a relatively moderate value when compared to previous studies (e.g., Hussmann et al, 2002;Tobie et al, 2003). Note that if tidal heating is neglected, a liquid layer can survive until the present.…”

Europa Lander Mission: A Challenge to Find Traces of Alien Life

“…Crater depth and morphology analysis (Greeley et al, 1998b;Schenk, 2002] provide estimates of the ice shell varying from few to 18-20 km. The extreme position in this debate, a thick shell of a few tens of kilometers likely convective in its lower part (e.g., Pappalardo et al, 1999) is supported by thermodynamic models (Hussmann et al, 2002;Tobie et al, 2003). The uncertainty in thickness translates directly into an uncertainty in the heat transfer mechanism: if the shell is thick, the rigid surface could be underlain by a layer of convecting water ice (e.g., Tobie et al, 2003;Showman and Han, 2004), whereas a thin shell would instead transport the heat by conduction, and can account for melting of water through the surface .…”