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Folie 1 Physical State of the Deep Interior of CoRoT-7b F. W. Wagner T. Rückriemen F. Sohl German Aerospace Center (DLR) IAU Symposium 276 - 13 October 2010

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Slide 2 What we know Introduction - Method - Results - Conclusions Mass and radius only known for two out of ~ 30 exoplanets below < 15 M Radius (1.58±0.10) R (Bruntt, et al. 2010) The mass challenge 1-4 M Pont, et al. 2010 (4.8±0.8) M Queloz, et al. 2009 (5.2±0.8) M Bruntt, et al. 2010 (5.7±2.5) M Boisse, et al. 2010 (6.9±1.4) M Hatzes, et al. 2010 Mean density (7.2±1.8) Mg m -3 (Bruntt, et al. 2010) rocky planet? The CoRoT Family M-R Relations CoRoT-7b GJ 1214b CoRoT-7b

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Slide 3 Interior Structure Model Introduction - Method - Results - Conclusions Mechanical Thermal Spherical and fully differentiated Mechanical equilibrium and thermal steady state Output: R p, m(r), g(r), p(r), (r), q(r), T(r) Input: M p, composition, P surf, T surf, T(r) conv.

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Slide 4 Mixing Length Formulation Introduction - Method - Results - Conclusions Heat flux l Effective thermal conductivity due to thermal convection T < T ref T > T ref Dynamic viscosity Local Nusselt number

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Slide 5 Internal Structure of CoRoT-7b Introduction - Method - Results - Conclusions Density Bulk composition Radius, R/R Core mass fraction, wt.% Mass, M/M Density suggests rocky bulk composition Earth-like Iron-depleted

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Slide 6 Present Thermal State of CoRoT-7b Introduction - Method - Results - Conclusions Pressure-induced sluggish convective regime in the lower mantle Substantial higher CMB temperatures in comparison to parameterized models Mantle pressures within stability field of post-perovskite (125 –1000 GPa) 5320K 5210K 6710K 7560K Temperature Pressure 727GPa 656GPa 1440GPa 1940GPa PCM (Valencia, et al. 2006)

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Slide 7 Radiogenic Heating Introduction - Method - Results - Conclusions Temperature CMB Specific heat production Deep interior stays relatively hot despite decreasing radiogenic heat production What is the role of accretional and tidal heating? Age: 1.2 – 2.3 Gyr (Leger, et al. 2009)

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Slide 8 Physical State of the Core Introduction - Method - Results - Conclusions Temperature strongly depending on rheology Relatively high activation volume needed to initiate core melting Solid state of lower mantle and iron core due to high pressure Activation volume, mantle Sulfur content, core 32.6 wt.% cmf ~3000K ~ 15 wt.% S Melting point reduction

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Slide 9 Conclusions Introduction - Method - Results - Conclusions The mean density of (7.2±1.8) Mg m -3 and high surface temperatures imply that CoRoT-7b is a dry and rocky planet. Post-perovskite is expected to be the predominant mantle mineralogical phase. Pressure-induced sluggish convection prevalent in the lower mantle. Due to the large effect of pressure on melting, a pure iron core is expected to be solid. But: A liquid core cannot completely be ruled out, depending strongly on mantle rheology and actual core composition.

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Slide 10 Thank you for your attention!

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Slide 11 Introduction - Method - Results - Conclusions Comparison with 2D Convection Model L. Noack 5M Deep interior High pressure Highly sluggish layer No lateral temperature variation from day-side to night-side Upper mantle Convection pattern strongly influenced by varying surface temperature 70 5,300K

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Slide 12 On the Existence of a Magma Ocean Introduction - Method - Results - Conclusions Temperature variation within the lithosphere less distinct Depth of a possible magma ocean depending on the predominant minerals and actual surface temperatures 1810K

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Slide 13 Introduction - Method - Results - Conclusions Equation of State Mao H., Hemley R.J., 2007: PNAS, 104, 9114-9115 Equation of State (EoS) relates pressure, temperature, and density Generalized Rydberg EoS (Stacey, 2005): Fit to high- pressure experiments Reciprocal K-primed EoS (Stacey, 2000): Fit to PREM Problem: Extrapolation exoplanets

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Chapter 12: Earth’s Interior

Chapter 12: Earth’s Interior

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