The interior of Enceladus one year after Cassini Gaël Choblet (1), Gabriel Tobie (1), Ondˇ rej ˇ Cadek (2), Christophe Sotin (3), Mathieu Bouffard (4), Frank Postberg (5), Mathilde Kervazo (1,3), Marie Bˇ ehounková (2) and Ondˇ rej Souˇ cek (6) (1) Laboratoire de Planétologie et Géodynamique, UMR-CNRS 6112, Université de Nantes, France, (2) Charles University, Department of Geophysics, Prague, Czech Republic, (3) Jet Propulsion Laboratory, Caltech, Pasadena, USA, (4) Max Planck Institute for Solar System Research, Göttingen, Germany, (5) Institut für Geowissenschaften, Universität Heidelberg, Germany, (6) Charles University, Mathematical Institute, Prague, Czech Republic. (gael.choblet@univ-nantes.fr) 1. Introduction While the observation of a large-scale plume emitted by Enceladus occurred early after the insertion of the Cassini spacecraft around Saturn, a coherent view on the interior processes that power and feed this activ- ity started emerging only in the latest year of the mis- sion. Thanks to a flexible payload as well as multi- ple flybys during the extended mission, analyses of Enceladus data (composition of materials originating from the moon’s interior [7, 8], geophysical measure- ments and long series of surface images [5, 9, 1]) com- posed a view where a global salty ocean is present un- derneath an ice crust of very uneven thickness (20-25 km in average, less than 5 km beneath the south pole, more than 30 km in some equatorial regions). Den- sity of the rock core implies a significant (∼ 20-30 %), water-filled, porosity. Furthermore, several inde- pendent chemical clues indicate that high-temperature (>363 K) hydrothermal processes probably occur at present, deep in the moon [4, 12]. 2. The vibrating hot sandy core [2] These observations require a huge heat power and a mechanism to focus the release of heat in the South Po- lar Terrain (SPT), most probably related to tidal dissi- pation yet unexplained by previous models. Assuming the ice shell thickness is known locally, a conductive thermal equilibrium provides a rough estimate of the heat emanating from Enceladus’ interior: while, in the SPT, tidal heating within the ice crust could match the local heat budget (3-5 GW) owing to an extremely thin shell and to the presence of faults [10], the consider- able amount of heat extracted elsewhere (i.e. at mod- erate and northern latitudes) exceeds 20 GW, a figure that requires a deeper origin since a thicker ice shell is less dissipative. Mechanical tests on water saturated unconsolidated rock materials subjected to cyclic deformation point to the likelihood that, at tidal frequency, a significant amount of energy can be dissipated in a rock core filled with interstitial liquid water. We show in 3D spherical simulations that thermal convection of in- terstitial water within such a tidally heated core leads to strongly focused hot upwellings, especially beneath the poles (Fig. 1). While the permeability of Ence- ladus’ core is unknown and could vary within a range involving orders of magnitude, modeled temperatures obtained for a relatively limited interval within the ad- missible parameter space (typically 10 -14 -10 -13 m 2 ) agree with the estimate inferred from compositional measurements by Cassini that indicate water-rock in- teraction. Powerful hotspots (several GW) are thus predicted at the seafloor with maxima located beneath the poles and along the leading and trailing meridians. 3. Polar ocean Plumes Ocean dynamics could partly filter this strongly het- erogeneous heat flux at the seafloor, mostly if rota- tional effects overcome thermal convection. We have recently conducted 3D simulations dedicated to the buried ocean of Enceladus with a heterogeneous heat flux prescribed at the inner boundary (not shown in [2]): while the precise balance between the Coriolis and the buoyancy forces is not known, our first results demonstrate that although in some cases, the heat flux pattern at the seafloor can be significantly blurred at moderate latitudes bounded by the the tangent cylin- der, it remains globally unaffected in polar regions where ocean plumes supply a significant amount of heat in regions coinciding with the lowest ice thick- ness (Fig. 1). Scaling relationships also indicate that EPSC Abstracts Vol. 12, EPSC2018-662, 2018 European Planetary Science Congress 2018 c  Author(s) 2018 E P S C European Planetary Science Congress