Europa Scenarios: Physical Models Ice-cracks on surface consistent with either “warm-ice” or water beneath the surface Near infrared mapping consistent with hydrated salts (Mc Cord et al. 2001) Magnetometer data from recent Galileo mission confirm presence of water (Kivelson et al., 2000) The main facts

Europa Scenarios: Physical Models Is there a water ocean beneath the iced surface? How deep is the ocean? How thick is the ice shell? What is the thermal structure of the moon? Is tidal heating important as in Io? Where? Is there life??? The main questions

Acquisition of seismic data has been proposed => need of physical models based on different composition and thermal structure (scenarios) We assume a three-layer composition: water-ice, silicatic mantle, metallic core consistent with the values of mass and moment of inertia The thermal structures are based on estimations of internal heating (radiogenic plus tidal heating) … we will see later on

water-iceComposition EOS used is the new standard international EOS for pure water: IAPWS- 95 (Wagner and Pruss, 2002) For ice (and sea-ice), we implemented the recent EOS from Feistel and Wagner (2005) We compare the pure water EOS with the updated sea-ice EOS (at low P): main effect is the reduction of the melting temperature. If other elements (e.g., ammonia) are present in the water-ice system, the melting T will be reduced favoring presence of a liquid water-rich ocean

Silicatic mantle Composition We use the recent thermodynamic consistent EOS for 5 oxides system (CFMAS) from (Stixrude and Lithgow-Bertelloni, 2005) implemented in PERPLEX (Connolly J.) We test 2 composition: pyrolite and L-LL type chondritic mantle 3 Gpa (lower Europa mantle), 1000 O C

Silicatic mantle Composition PyroliteL-LL type chondrite Density is lower for pyrolite than for low-iron chondrite Uncertainties in density are between 0.1 and 0.2% at P-T of the Europa mantle (Cammarano et al., 2003)

Silicatic mantle Composition PyroliteL-LL type chondrite And V P,S are higher for pyrolite. Note the stability fields of plagiocase and spinel at low pressure

Silicatic mantle Composition Remaining issues: Hydrous minerals stable at P-T range of Europa mantle (antigorite, brucite, etc.) would have an effect of reducing density, seismic velocity, and reducing the melting temperature. This means that hot scenario is favored. Note that at low P, presence of hydrous minerals is favoured at low T, but at high T a process of loosing water may happen… therefore the role of hydrous minerals can be excluded… this can explain partially the presence of the Europa ocean… The phase diagram can change slighlty, but still olivine would be present together with Antigorite and A

Silicatic mantle Composition

Silicatic mantle Composition

Metallic CoreComposition We test either a pure iron (high-density, high melting T) or a mix of iron+sulfur (20%) core. Note that a solid iron core cannot contain more than 0.1% of light elements at core P (not exceeding 5.5 GPa) => if T is low enough, a solid iron may be favored Elastic data have been selected for stable iron phases (  ) and liquid iron Data on eutectic melting T, its change with pressure and density change as function of S content at correct P-T range have been compiled (Sanloup et al., 2003, Boheler 1996) I thank Sebastien Merkel for the help given to select these data Pressure (Gpa)

Thermal structures solidus + Hot Cold Conductive curves for uniform internal heating in the mantle

Thermal structures Cold, conductive mantle coupled with solid iron core Hot convective mantle, with either no bottom boundary layer (no heat from the core, but only internal, maybe localized in the upper part) or with (  T=400 K). Coupled with melted Fe+S core Isothermal structure in the core

Thermal structures 1) Uncertainties in mantle thermal structure due to different CM boundary of km (reference is 835km) 2) Difference in mantle thermal structure due to a variations in density, between 3300 (circa pyrolite, solid line) to 3400 (circa L-LL chondrite, dashed) 1)2)

Thermal structures Shallow thermal structures have been tuned for testing different thickness of the ice shell.

Inversion for ocean and CM boundary depth Example of g approximate profile

Inversion for ocean and CM boundary depth Cold scenario, pyrolitic mantle, pure iron core

Inversion for ocean and CM boundary depth Cold scenario, pyrolitic mantle, pure iron core

Inversion for ocean and CM boundary depth Cold scenario, pyrolitic mantle, pure iron core

Inversion for ocean and CM boundary depth Ocean depth increase of circa 10km if mantle is chondritic (higher density) instead than pyrolitic

Inversion for ocean and CM boundary depth Ocean depth is similar in hot or cold scenarios

The physical models Hot Cold (Pyrolitic mantle)

The physical models

Temperature dependence of Q confers very different dissipations between the cold and hot scenarios Cammarano et al., 2003 An useful homologous temperature scaling is:

Conclusions Due to feeback between radiogenic and tidal heating, either hot or cold scenarios may be developed on Europa. We found a set of physical models for different scenarios (hot vs cold) that are consistent with mass and moment of inertia The ocean depth is constrained between 100 and 140, consistent with the result of Anderson (2000). Strong dissipation and dispersion Case for occurrence of partial melt => volcanism ? Possible source of EQ at lithospheric depths Large(r) 3-D variation of seismic velocities related to large  T to the mantle convection Possible case for a melted core of iron plus light elements HOT scenario

Discussion Geodynamic models for the hot case should allow to assess the thickness of boundary layer and the degree of heterogeneity of the 3D structure. Perhaps it would also give indications about eventual strong mantle flow that will confer anisotropy… Test of different thermal models? What kind Assess better the thermal structure of the ice shell, by computing how effect of tidal heating change with thickness of ice (recent literature exists) and so compute the heat flow Possible Earthquakes source at a different depths for the two scenarios. In cold case brittle failure may happen below, not so in the hot mantle. EQ similar to moonquakes are possible. Use magnetic field constraints The seismic response of the physical models??? TO BE CONTINUED….

Effect of distance Lp at 45sec

Effect of distance Lp at 20sec

Effect of distance Lp at 100sec

Effect of shell thickness (5 km, 10km, 20km, 40km)