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

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 (4.8±0.8) M  Queloz, et al (5.2±0.8) M  Bruntt, et al (5.7±2.5) M  Boisse, et al (6.9±1.4) M  Hatzes, et al  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

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.

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

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

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)

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)

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

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.

Slide 10 Thank you for your attention!

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 

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

Slide 13 Introduction - Method - Results - Conclusions Equation of State Mao H., Hemley R.J., 2007: PNAS, 104, 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