Px dominated Tue, 17 Sep, 17:15–18:45 | L2.67 Earth-like...
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Non-Cognitive Predictors of Student Success: A Predictive Validity Comparison Between Domestic and International Students Non-Cognitive Predictors of Student Success: A Predictive Validity Comparison Between Domestic and International Students INTRODUCTION Discoveries of silicate-metal worlds around other stars have inspired diverse geophysical models of their plausible structures and tectonic regimes [1]. These models are severely hampered, however, by inexact assumptions about long-lived radiogenic heat production ( 235,238 U, 232 Th, 40 K) and inventories of rock-forming elements (e.g. Si, Al, Fe, Ca, Na, Mg). Host stars of planets ought to broadly reflect the overall compositions of planetary systems [2,3; Figure 1]: to date, the only confirmed connection between stellar host abundances and planets is the presence of Jupiter-mass worlds around stars with enriched [Fe/H] content [e.g. 4]. Otherwise, stellar metallicity is a poor predictor of the likeliness of hosting terrestrial-type planets [5; Figure 2]. Planets form in a compositional gradient dictated by thermodynamical equilibrium in the disc and the chemical composition and temperature of the newly formed central star, and mixing-in of intrinsic and extrinsic material in the stellar birth cluster. Key elements within the planet govern mantle processes, and thus the nature of its crust, composition of atmosphere and retention of a hydrosphere [e.g. 6,7]. For example, without plate recycling dictated by mantle rheology (internal heat, mineralogy, water content) a carbon cycle is unlikely. To better understand the geodynamical nature of exoplanets to make predictions about observations of such phenomena and M-r and atmospheric compositions, we must understand how differences in stellar host compositions would be reflected in the evolution of exoplanets [e.g. 8]. Here, I show how Galactic Chemical Evolution (GCE) models of star (and planet) age and composition yield different effects on geodynamical regimes. The geodynamical consequences of these differences are discussed in the following sections. EARTH-LIKE EXOPLANETARY MANTLES Recent [8-10] GCE codes: (1) improve models for the evolution of radiogenic heating in rocky exoplanets and (2) assess the geophysical effects of different rock-forming element inventories (e.g. Mg/Si; Figure 3) emphasizing factors that affect geodynamic regimes (e.g. mantle properties, heat production, crust type). Cosmochemically Earth-like exoplanets Stephen J. Mojzsis 1,2 [email protected] http://isotope.colorado.edu 1. CRiO, Geological Sciences, University of Colorado 2. Hungarian Academy of Sciences SEE THE PRESENTATION: EPSC-DPS2019-1460 | Orals | EXO2 Constraining the range of bulk terrestrial exoplanet compositions, and their effects on coupled interior- atmosphere evolution by Robert Spaargaren, Maxim Ballmer, Stephen Mojzsis, Daniel Bower, Caroline Dorn, and Paul Tackley Tue, 17 Sep, 11:15–11:30 Venus (Room 6) Figure 1. The similarity of meteoritic and photospheric abundances is evident in this figure for our solar values vs. terrestrial compositions. Abundances have been normalized to 10 6 atoms of Si. Points along the diagonal have near-identical abundances in both meteoritic and photospheric data sets. Elemental abundances above the diagonal are depleted in CI chondrites (N, C, O, H and noble gases). Elemental abundances below the diagonal are depleted in the Sun (Li). [from ref. 3] Figure 2. Mass-radius relation for known low-mass exoplanets. The spread indicates a variety in density. Here, the very large uncertainties for radius and mass are omitted. Simple interior structure estimates are also shown by colored lines. The intensity in color of the dots indicates the metallicity (Fe/H ratio) of the host star as shown in the legend bar at right. (Data source: www.exoplanet.eu).[see ref. 5] Figure 3. observed variations in stellar compositions of FGKM stars from spectrographic measurements (translucent red dots). Compositions are taken from the Hypatia catalogue [11]. Solar- system composition is marked by the yellow diamond [12]. Subsequent work reported here neglects the M-stars in the analysis. EPSC-DPS2019-1952 | EXO2 Tue, 17 Sep, 17:15–18:45 | L2.67 THEORY AND PRACTICE Key processes related to the geodynamics of “Earth-like” rocky planets begin with mantle compositions which result in different geodynamical states [6-8]. The most important physical property for planetary interiors is viscosity, which can differ by orders of magnitude between different minerals. The six most abundant rock-forming elements in the Sun are Si, Mg, Fe, S, Al and Ca. The first most important ratio for mineralogy is the magnesium to silicon (MgO:SiO 2 ) ratio. The argument: (i) Earth’s Primitive Mantle [Mg/Si] is ~1.03 (CI=0.93); (ii) The dominant upper mantle (UM) phase of that composition is olivine (Mg,Fe) 2 (SiO 4 ) for which no lattice site can accommodate Fe 3+ ; (iii) If Earth had inherited a slightly lower [Mg/Si] (e.g. <0.9), pyroxene ((XY(Si,Al) 2 O 6 , where X represents divalent Ca, Mg and Fe, and Y represents trivalent Cr, Al, Fe) would dominate. Pyroxene takes up Fe 3+ into its structure and with substitutions maintains low activity of Fe 3+ and a very low oxygen fugacity; (iv) Owing to (ii), the Fe 3+ present in the Earth’s UM goes into spinel ((Mg,Fe)Al 2 O 4 ) such that there is a modal phase imposing a high oxygen fugacity (~FMQ) on gases in equilibrium with rock; (v) Consequently, for the entirety of the geologic record it seems that Earth’s UM always degassed a relatively oxidized form of carbon (CO- CO 2 ) rather than an alternative mantle which would degas CH 4 -CO [e.g. 13]. The consequences: The Earth’s lower mantle contains different minerals and is dominated by bridgemanite perovskite (MgSiO 3 ) which has a several orders-of- magnitude higher viscosity than the second most important mineral, magnesiowüstite (MgO). In this case, an increase in MgO fraction would lead to magnesiowüstite dominating the rheology and the overall strength of the LM being much weaker. These arguments consider only MgO and SiO 2 ; other important oxides such as FeO, CaO, Al 2 O 3 also affect the mineralogy and physical properties and warrant study. An increase in viscosity results in a hotter planet with more melting, whereas a decrease in viscosity results in a cooler planet. In turn, along with age, this affects the likelihood of the planet developing and sustaining plate recylcing. CONCLUSIONS In metal+silicate planets, subtle changes in [Mg/Si] vs. [Fe/H] for different stellar sources of different ages should make the difference between a CH 4 vs. CO 2 atmosphere and a fluid, convecting (pure olivine) interior vs. a stiff, non- convecting (pure pyroxene), mantle [Figures 4-7]. REFERENCES [1] Laughlin G. and Lissauer J.L. (2015) Treatise on Geophysics, 2nd edition. [2] Goldschmidt V. M. (1937) Norske vidensk. – akad. Oslo, Mat.-Nat. Klass, 4, 1-148. [3] Wang H.-Y. et al. (2019) MNRAS 482, 2, 2222–2233. [4] Fischer D.A. and Valenti J. (2005) Astrophys. J. 622, 1102-1117. [5] Berg et al. (2009) Astrophys. J. 702, L172. [6] Ringwood A.E. (1989) EPSL, 95, 1-7. [7] Palme H. and O'Neill H. St. C. (2014) Treatise on Geochemistry, 2nd edition. DOI/10.1016/B978-0-08-095975-7.00201-1. [8] Frank E.A. et al. (2014) Icarus 243, 274-286. [9] Côté B. et al. (2016) Astrophys. J. 824, 82. doi:10.3847/0004- 637X/824/2/82 [10] Lugaro M. et al. (2018) Prog. Part. Nucl. Phys. 102, 1-47. [11] Hinkel N.R. et al. (2014) AJ. 148 (3) L54. [12] Asplund M. et al. (2005) [13] Trail D. et al. (2011) Nature, 480, 79-82. [14] Adebekyan V. Zh. et al. (2012) A&A 545, A32. Figure 4. Mass fractions of some major mantle-forming elements. In the analytical Clayton model described in ref. 8, these are primary species that experience a constant state of enrichment in the gas since the gas is initially metal-free and have concentrations that are fit to CI values at Solar System formation.[from ref. 8] Figure 5. Mass fraction evolution of Fe in gas. Initially, it is only produced in massive stars, but 1 Gyr after formation, Type Ia supernovae begin contributing Fe to the gas, boosting its production rate.[8] Figure 6 Plot of the Mg/Si ratio in solar systems that form around Sun-like stars using a new multi-zone GCE calculations incorporating stellar lifetimes. As with Fe in Figure 5, initially, Si is more effectively produced in massive stars, and as Type Ia supernovae begin contributing more Si to the ISM gas, the ratio of Mg/Si declines with the boosted concentration of Si.[unpublished manuscript] -1.5 -1.0 -0.5 0.0 0.5 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 [Mg/Si] relative to solar value [Fe/H]* n=1111 FGK stars -1.5 -1.0 -0.5 0.0 0.5 1.0 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Al Ca solar Z (dex) relative to solar value [Fe/H] (dex) solar -1.5 -1.0 -0.5 0.0 0.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 n=1111 FGK stars Mg Si solar Z (dex) relative to solar value [Fe/H] (dex) solar Figure 7 (A). Si/Fe mass fraction ratio over galactic history. Early in the Galaxy’s history (t < 1 Gyr), the ratio decreases while Si and Fe are both being produced in massive stars, but when Type Ia supernovae begin exploding, the production of Fe increases, leading to declining Si/Fe. (B). Model output of Mg/Si vs. Fe/H [from ref. 8]. (C). [Mg] and [Si] as well as (D) [Al] and [Ca] plotted against [Fe/H] for 1111 FGK stars from ref. 16. (D). Data compilation of ratios, compare to (B). 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Frank et al. (2014) solar value (CI) [Mg/Si]* [Fe/H]* A B C D E Px dominated Ol dominated
Transcript of Px dominated Tue, 17 Sep, 17:15–18:45 | L2.67 Earth-like...
Non-Cognitive Predictors of Student Success:A Predictive Validity Comparison Between Domestic and International Students
Non-Cognitive Predictors of Student Success:A Predictive Validity Comparison Between Domestic and International Students
INTRODUCTIONDiscoveries of silicate-metal worlds around other stars haveinspired diverse geophysical models of their plausiblestructures and tectonic regimes [1]. These models areseverely hampered, however, by inexact assumptions aboutlong-lived radiogenic heat production (235,238U, 232Th, 40K) andinventories of rock-forming elements (e.g. Si, Al, Fe, Ca, Na,Mg).
Host stars of planets ought to broadly reflect the overallcompositions of planetary systems [2,3; Figure 1]: to date, theonly confirmed connection between stellar host abundancesand planets is the presence of Jupiter-mass worlds aroundstars with enriched [Fe/H] content [e.g. 4]. Otherwise, stellarmetallicity is a poor predictor of the likeliness of hostingterrestrial-type planets [5; Figure 2]. Planets form in acompositional gradient dictated by thermodynamicalequilibrium in the disc and the chemical composition andtemperature of the newly formed central star, and mixing-inof intrinsic and extrinsic material in the stellar birth cluster.
Key elements within the planet govern mantle processes, andthus the nature of its crust, composition of atmosphere andretention of a hydrosphere [e.g. 6,7]. For example, withoutplate recycling dictated by mantle rheology (internal heat,mineralogy, water content) a carbon cycle is unlikely.
To better understand the geodynamical nature of exoplanetsto make predictions about observations of such phenomenaand M-r and atmospheric compositions, we must understandhow differences in stellar host compositions would bereflected in the evolution of exoplanets [e.g. 8].
Here, I show how Galactic Chemical Evolution (GCE) models ofstar (and planet) age and composition yield different effectson geodynamical regimes. The geodynamical consequences ofthese differences are discussed in the following sections.
EARTH-LIKE EXOPLANETARY MANTLESRecent [8-10] GCE codes: (1) improve models for theevolution of radiogenic heating in rocky exoplanets and (2)assess the geophysical effects of different rock-formingelement inventories (e.g. Mg/Si; Figure 3) emphasizing factorsthat affect geodynamic regimes (e.g. mantle properties, heatproduction, crust type).
Cosmochemically Earth-like exoplanets
Stephen J. Mojzsis1,2
[email protected] http://isotope.colorado.edu
1. CRiO, Geological Sciences, University of Colorado2. Hungarian Academy of Sciences
SEE THE PRESENTATION: EPSC-DPS2019-1460 | Orals | EXO2Constraining the range of bulk terrestrial exoplanet compositions, and their effects on coupled interior-atmosphere evolution
by Robert Spaargaren, Maxim Ballmer, Stephen Mojzsis, Daniel Bower, Caroline Dorn, and Paul TackleyTue, 17 Sep, 11:15–11:30 Venus (Room 6)
Figure 1. The similarity of meteoritic and photosphericabundances is evident in this figure for our solar valuesvs. terrestrial compositions. Abundances have beennormalized to 106 atoms of Si. Points along the diagonalhave near-identical abundances in both meteoritic andphotospheric data sets. Elemental abundances above thediagonal are depleted in CI chondrites (N, C, O, H andnoble gases). Elemental abundances below the diagonalare depleted in the Sun (Li). [from ref. 3]
Figure 2. Mass-radius relation for known low-massexoplanets. The spread indicates a variety in density. Here,the very large uncertainties for radius and mass are omitted.Simple interior structure estimates are also shown by coloredlines. The intensity in color of the dots indicates themetallicity (Fe/H ratio) of the host star as shown in the legendbar at right. (Data source: www.exoplanet.eu).[see ref. 5]
Figure 3. observed variations in stellar compositions of FGKM starsfrom spectrographic measurements (translucent red dots).Compositions are taken from the Hypatia catalogue [11]. Solar-system composition is marked by the yellow diamond [12].Subsequent work reported here neglects the M-stars in the analysis.
EPSC-DPS2019-1952 | EXO2Tue, 17 Sep, 17:15–18:45 | L2.67
THEORY AND PRACTICEKey processes related to the geodynamics of “Earth-like”rocky planets begin with mantle compositions which resultin different geodynamical states [6-8]. The most importantphysical property for planetary interiors is viscosity, whichcan differ by orders of magnitude between differentminerals. The six most abundant rock-forming elements inthe Sun are Si, Mg, Fe, S, Al and Ca. The first mostimportant ratio for mineralogy is the magnesium to silicon(MgO:SiO2) ratio.
The argument: (i) Earth’s Primitive Mantle [Mg/Si] is ~1.03(CI=0.93); (ii) The dominant upper mantle (UM) phase ofthat composition is olivine (Mg,Fe)2(SiO4) for which nolattice site can accommodate Fe3+; (iii) If Earth had inheriteda slightly lower [Mg/Si] (e.g. <0.9), pyroxene ((XY(Si,Al)2O6,where X represents divalent Ca, Mg and Fe, and Yrepresents trivalent Cr, Al, Fe) would dominate. Pyroxenetakes up Fe3+ into its structure and with substitutionsmaintains low activity of Fe3+ and a very low oxygenfugacity; (iv) Owing to (ii), the Fe3+ present in the Earth’sUM goes into spinel ((Mg,Fe)Al2O4) such that there is amodal phase imposing a high oxygen fugacity (~FMQ) ongases in equilibrium with rock; (v) Consequently, for theentirety of the geologic record it seems that Earth’s UMalways degassed a relatively oxidized form of carbon (CO-CO2) rather than an alternative mantle which would degasCH4-CO [e.g. 13].
The consequences: The Earth’s lower mantle containsdifferent minerals and is dominated by bridgemaniteperovskite (MgSiO3) which has a several orders-of-magnitude higher viscosity than the second most importantmineral, magnesiowüstite (MgO). In this case, an increase inMgO fraction would lead to magnesiowüstite dominatingthe rheology and the overall strength of the LM being muchweaker. These arguments consider only MgO and SiO2;other important oxides such as FeO, CaO, Al2O3 also affectthe mineralogy and physical properties and warrant study.An increase in viscosity results in a hotter planet with moremelting, whereas a decrease in viscosity results in a coolerplanet. In turn, along with age, this affects the likelihood ofthe planet developing and sustaining plate recylcing.
CONCLUSIONSIn metal+silicate planets, subtle changes in [Mg/Si] vs.[Fe/H] for different stellar sources of different ages shouldmake the difference between a CH4 vs. CO2 atmosphere anda fluid, convecting (pure olivine) interior vs. a stiff, non-convecting (pure pyroxene), mantle [Figures 4-7].
REFERENCES[1] Laughlin G. and Lissauer J.L. (2015) Treatise on Geophysics, 2nd edition.[2] Goldschmidt V. M. (1937) Norske vidensk. – akad. Oslo, Mat.-Nat. Klass,4, 1-148.[3] Wang H.-Y. et al. (2019) MNRAS 482, 2, 2222–2233.[4] Fischer D.A. and Valenti J. (2005) Astrophys. J. 622, 1102-1117.[5] Berg et al. (2009) Astrophys. J. 702, L172.[6] Ringwood A.E. (1989) EPSL, 95, 1-7.[7] Palme H. and O'Neill H. St. C. (2014) Treatise on Geochemistry, 2ndedition. DOI/10.1016/B978-0-08-095975-7.00201-1.[8] Frank E.A. et al. (2014) Icarus 243, 274-286.[9] Côté B. et al. (2016) Astrophys. J. 824, 82. doi:10.3847/0004-637X/824/2/82[10] Lugaro M. et al. (2018) Prog. Part. Nucl. Phys. 102, 1-47.[11] Hinkel N.R. et al. (2014) AJ. 148 (3) L54.[12] Asplund M. et al. (2005)[13] Trail D. et al. (2011) Nature, 480, 79-82.[14] Adebekyan V. Zh. et al. (2012) A&A 545, A32.
Figure 4. Mass fractions of some major mantle-formingelements. In the analytical Clayton model described in ref.8, these are primary species that experience a constantstate of enrichment in the gas since the gas is initiallymetal-free and have concentrations that are fit to CI valuesat Solar System formation.[from ref. 8]
Figure 5. Mass fraction evolution of Fe in gas. Initially, it isonly produced in massive stars, but 1 Gyr after formation,Type Ia supernovae begin contributing Fe to the gas,boosting its production rate.[8]
Figure 6 Plot of the Mg/Si ratio in solar systems that form aroundSun-like stars using a new multi-zone GCE calculationsincorporating stellar lifetimes. As with Fe in Figure 5, initially, Si ismore effectively produced in massive stars, and as Type Iasupernovae begin contributing more Si to the ISM gas, the ratio ofMg/Si declines with the boosted concentration of Si.[unpublishedmanuscript]
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Figure 7 (A). Si/Fe mass fraction ratio over galactic history. Early in the Galaxy’s history (t < 1 Gyr), the ratio decreaseswhile Si and Fe are both being produced in massive stars, but when Type Ia supernovae begin exploding, the productionof Fe increases, leading to declining Si/Fe. (B). Model output of Mg/Si vs. Fe/H [from ref. 8]. (C). [Mg] and [Si] as well as(D) [Al] and [Ca] plotted against [Fe/H] for 1111 FGK stars from ref. 16. (D). Data compilation of ratios, compare to (B).
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