europa scenarios

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Europa Scenarios: Physical Models

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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

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Acquisition of seismic data has been proposed => need of physical models based on different composition and thermal structure (scenarios)

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water-ice Composition 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

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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

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Silicatic mantle Composition Pyrolite L-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)

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

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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

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Silicatic mantle Composition

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Silicatic mantle Composition

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Metallic Core Composition 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

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Thermal structures solidus <Qr> <Qr> + <Qi> Hot Cold Conductive curves for uniform internal heating in the mantle

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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

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Thermal structures 1) Uncertainties in mantle thermal structure due to different CM boundary of +-100 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)

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

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

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

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

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

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

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

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The physical models Hot Cold (Pyrolitic mantle)

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The physical models

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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:

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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).

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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….

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Effect of distance Lp at 45sec

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Effect of distance Lp at 20sec

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Effect of distance Lp at 100sec

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

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