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The Effect of Abundance Ratios on Rocky Planet Structure Wendy Panero Ohio State University The Effect of Abundance Ratios on Rocky Planet Structure Wendy Panero Ohio State University JNKMA JB 5 5AAC=I Earth Structure Two Major Divisions: *The silicate Earth: The crust and mantle are composed of silicate ceramics. *The core: Primarily iron, with some Ni and “light” elements Hidden from direct sampling. Composition of the (Silicate) Earth 1 Silicate Earth/Chondrite Mg Ca Ti REE Si Sc Al Zr V Li Cr Na Mn K Fe W Rb Co Cu Ni Identical to Chondrites F Zn 0.1 In Cd Hg Tl 0.01 Pb Bi Ag Cl Mo As Br Au C 0.001 0 Pd Rh Pt Ru Ir Re Os S Se Te 500 1000 1500 50% Condensation Temperature (T) 2000 Earth Structure *The silicate Earth: Solid convective motions in the mantle give rise to melting at the surface, sinking of dense oceanic crust creating plate tectonics. Earth Mantle Dynamics & Surface Plate Tectonics 3.8 3.6 Basalt-Eclogite transition 3 Density (g/cm ) Earth Composition 3.4 3.2 3.0 Mantle Density Basalt Density (5% mantle melt) 2.8 0 2 4 6 8 Pressure (GPa) Kelloggetetal., al.,1999 1999 Kellogg Earth Mantle Dynamics gρ 2α HD 5 Ra = ηκ k H radiogenic heat production η Viscosity (fxn composition, T) D Layer thickness Mantle Concentrations of radioactive isotopes 238U 235U 232Th 40K 20 ppb 1 ppb 100 ppb 280 ppm Kellogg et al., 1999 Planetary Dynamics from Interior Heat Production K U Th total Compositional variation in exoplanet hosts 7 6 Known planet hosts 5 4 uncertainty NAl/NSi 3 2 SUN 0.1 9 8 7 6 5 4 5 6 7 8 9 1 2 NMg/NSi Data from Adibekyan et al., 2012 Trace Element Variation? Thorium variation in Solar Analogues With known planets Without known planets Unterborn, Johnson, Panero in review Thorium variation in Solar Analogues 4 Figure 2. Stars with observed planets are shown as closed squares and without as un of Th as a function of Fe. The solid line represents*Factor the bestoffit~3 to those stars belo Unterborn, Johnson, Panero in review Abundance of Th as a function relationship. Center: of average variation in Si Thabundance content adop abundance. For each plot stars with observed planets are shown as closed squares a Thorium variation in Solar Analogues closed squares and without as unfilled squares. The Sun is shown for reference as a triangle. Left: Abunda of ~3 represents a one-to ts the best fit to those stars belonging to the high Fe, high Th group*Factor and the dashed on of average Si abundance adopting the same legend as in Th vs Fe.variation Right: Th/Si function of averag in as Tha content ts are shown as closed squares and without as unfilled squares. The Sun is shown for reference as a triang Unterborn, Johnson, Panero in review Thorium variation in Terrestrial Planets K U Th total Internal Heat Production Potential Range Earth ! Thorium variation in Terrestrial Planets Unterborn, Johnson, Panero in review Compositional variation in exoplanet hosts: Major Element Variation 7 6 Known planet hosts 5 4 uncertainty NAl/NSi 3 2 SUN 0.1 9 8 7 6 5 4 5 6 7 8 9 1 NMg/NSi 2 Data from Adibekyan et al., 2012 Mantle Mineral Primer Olivine + polymorphs β-ol, γ-ol (aka Wadsleyite and Ringwoodite) (Mg,Fe)SiO4 Holds water (1-2 wt% H2O) Breaks down to bridgmanite and ferropericlase ~25 GPa Bridgmanite (Mg,Fe)SiO3 Stable > 25 GPa (aka Mg-Si perovskite) Doesn’t hold water. Stiff. Ferropericlase (aka magnesiowüstite) (Mg,Fe)O Doesn’t hold water. Weak. Garnet (aka majorite, pyrope, almandine, spessartine, andradite, grossular, uvarite) A3B2Si3O12 Holds a little water. Breaks down to bridgmanite ~30 GPa Earth Mantle Mineralogy 1.0 fp Earth Phase Fraction (%) 0.8 α-ol 0.6 β-ol γ-ol pv br 0.4 0.2 gt opx cpx 0.0 cpv 5 10 15 20 25 30 35 Pressure (GPa) Calculated mineralogy for pyrolitic MgO, FeO, SiO2, CaO, Al2O3, Na2O system along a 1600 K adiabat using HeFESTo (Stixrude and Lithgow-Bertelloni 2007) Water capacity ~10x Earth surface oceans, mostly in olivine MgO likely changes its structure from B1 to B2 at (0.5 TPa. wever, in the previous work by Karato (1989), creep strength materials with B2 structure was not considered. Here, I examine differences in high-temperature creep behavior in materials h these two structures. Two different data sets are available ompare the difference in viscosity between B1 and B2 struce. First is a comparison of high-temperature power-law creep avior between NaCl (Franssen, 1994) 2 5 and CsCl (Heard and by, 1981) (Fig. 6a). Compared at the same normalized conditions, l shows substantially smaller creep strength than NaCl (by a fac- Earth Mantle Dynamics H radiogenic heat production η Viscosity (fxn composition, T) D Layer thickness gρ α HD Ra = ηκ k T / Tm 0.9 0.8 0.7 0.6 10 -5 s-1 -3 pe ro vs ki σ/µ te 10 sp in el ga ol rn iv et in e 10 -2 10 ro -4 10 me lt sa k c s tal -5 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Tm / T Karato, 2011 5. The crystal structure versus creep strength systematics for various materials power-law dislocation creep (based on Frost and Ashby (1982) and Karato 9)). Normalized stress (r/l, r: deviatoric stress, l: shear modulus) is plotted nst normalized temperature (Tm/T, T: temperature, Tm: melting temperature) strain-rate of 10$5 s$1. The results for metals include those with fcc, bcc and Kellogg et al., 1999 MgO likely changes its structure from B1 to B2 at (0.5 TPa. wever, in the previous work by Karato (1989), creep strength materials with B2 structure was not considered. Here, I examine differences in high-temperature creep behavior in materials h these two structures. Two different data sets are available ompare the difference in viscosity between B1 and B2 struce. First is a comparison of high-temperature power-law creep avior between NaCl (Franssen, 1994) 2 5 and CsCl (Heard and by, 1981) (Fig. 6a). Compared at the same normalized conditions, l shows substantially smaller creep strength than NaCl (by a fac- Earth Mantle Dynamics H radiogenic heat production η Viscosity (fxn composition, T) D Layer thickness gρ HD Ra = ηα k T / Tm 0.9 0.8 0.7 0.6 10 -5 s-1 -3 pe ro vs ki σ/µ te 10 sp in el ga ol rn iv et in e 10 -2 10 ro -4 10 me lt sa k c s tal -5 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Tm / T Karato, 2011 5. The crystal structure versus creep strength systematics for various materials power-law dislocation creep (based on Frost and Ashby (1982) and Karato 9)). Normalized stress (r/l, r: deviatoric stress, l: shear modulus) is plotted nst normalized temperature (Tm/T, T: temperature, Tm: melting temperature) strain-rate of 10$5 s$1. The results for metals include those with fcc, bcc and Kellogg et al., 1999 Mantle Mineral Primer “Wet” Dry Weak Strong Composition Controls Water Storage 1.0 (Si/Mg)=0.4(Si/Mg)Earth Phase Fraction 0.8 fp 0.6 α−Ol β−Ol γ−Ol cf 0.4 br 0.2 0.0 gt cpv 5 10 15 20 25 30 35 Pressure (GPa) Dominated by ferropericlase; ~1 ocean of water capacity Very weak mantle throughout Composition Controls Water Storage 1.0 (Si/Mg)=2.0(Si/Mg)Earth Phase Fraction (%) 0.8 c2c br 0.6 opx gt 0.4 0.2 cpx SiO2-stishovite 0.0 5 10 15 20 25 30 35 Pressure (GPa) No olivine or ferropericlase; ~0.1 ocean of water capacity Very stiff mantle throughout Compositional Impact on Plate Tectonics 3.8 3.6 Basalt-Eclogite transition 3 Density (g/cm ) Earth Composition 3.4 (Si/Mg)=1.6(Si/Mg)Earth 3.2 3.0 Mantle Density "Basalt" Density (5% mantle melt) 2.8 0 2 4 Pressure (GPa) 6 8