Predicted bulk compositions and geodynamical properties of terrestrial exoplanets in the Solar neighbourhood

2021 ◽  
Author(s):  
Rob Spaargaren ◽  
Haiyang Wang ◽  
Maxim Ballmer ◽  
Stephen Mojzsis ◽  
Paul Tackley
Keyword(s):  
Physical Properties ◽  
Plate Tectonics ◽  
Chemical Exchange ◽  
Full Range ◽  
Bulk Composition ◽  
Atmospheric Composition ◽  
Solar Neighbourhood ◽  
Stellar Abundances ◽  
Surface Conditions ◽  
End Members

<p>Our knowledge of the physical, chemical, and mechanical (i.e., rheological) properties of terrestrial planets is based almost entirely on our Solar System. Terrestrial exoplanets, however, show a startling diversity compared to our local experience. This observation challenges our understanding of terrestrial planet formation and of the thermal and mechanical behaviour of such worlds, some of which are vastly different from our own. To better understand the range and consequences of exoplanetary diversity, we integrate results from astrophysical models and observations, geodynamical simulations, and petrological experiments. Terrestrial exoplanet modelling requires plausible constraints to be placed on bulk planet compositions; bulk composition modulates interior properties, including core size, mantle mineralogy, and mantle melting behaviour. This may in turn affect the interaction between the planet’s interior and atmosphere, and thereby impact its potential to host a biosphere. Bulk composition may leave a signature on the mass and composition of the atmosphere, which could be detected in the future.</p><p>Here, we constrain exoplanetary diversity in terms of bulk planet composition, based on observations of stellar abundances in the Solar neighbourhood. We apply the devolatilization/fractionation trend between a planet and its host star [Wang+, 2019], to stellar abundances from the Hypatia catalogue [Hinkel+, 2014]. After applying a simplified model of rock-metal differentiation, we predict bulk planet and bulk silicate compositions of hypothetical exoplanets in the habitable zones of nearby stars. We further select 20 end-member compositions that span the full range of hypothetical bulk compositions based on our analysis.</p><p>With the compositions of these 20 end-members and by assuming Earth-like planetary masses and radii, we infer mineralogy and density profiles, as well as physical properties (e.g., viscosity) of the mantle using thermodynamic model Perple_X [Connolly, 2005]. These profiles and physical properties are prescribed in geodynamical models of exoplanet mantle evolution. We use convection code StagYY [Tackley, 2008] to model mantle convection and surface tectonic behaviour in a 2D spherical annulus geometry. We find that mantle viscosity increases with decreasing Mg:Si ratio of mantle rocks, with strong effects on planetary cooling and the likelihood of plate tectonics. In turn, the propensity of plate tectonics regulates the heat and chemical exchange between mantle and crust, affecting surface conditions and, by extension, atmospheric composition. This establishes a link between interior composition and surface conditions, and shows the importance of studying this aspect of planetary diversity. We recommend our 20 suggested end-members of terrestrial exoplanet compositions for subsequent modelling work.</p>

Jahnsite—whiteite solid solutions and associated minerals in the phosphate pegmatite at Hagendorf-Süd, Bavaria, Germany

2010 ◽  
Vol 74 (6) ◽  
pp. 969-978 ◽  
Author(s):  
I. E. Grey ◽  
W. G. Mumme ◽  
S. M. Neville ◽  
N. C. Wilson ◽  
W. D. Birch
Keyword(s):  
Electron Microscopy ◽  
Solid Solutions ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Full Range ◽  
Intensity Data ◽  
Compositional Zoning ◽  
Phosphate Mineral ◽  
End Members ◽  
Scanning Electron

AbstractSecondary phosphate assemblages from the Hagendorf Süd granitic pegmatite, containing the new Mn-Al phosphate mineral, nordgauite, have been characterized using scanning electron microscopy and electron microprobe analysis. Nordgauite nodules enclose crystals of the jahnsite—whiteite group of minerals, showing pronounced compositional zoning, spanning the full range of Fe/Al ratios between jahnsite and whiteite. The whiteite-rich members are F-bearing, whereas the jahnsite-rich members contain no F. Associated minerals include sphalerite, apatite, parascholzite, zwieselite-triplite solid solutions and a kingsmountite-related mineral. The average compositions of whiteite and jahnsite from different zoned regions correspond to jahnsite-(CaMnMn), whiteite-(CaMnMn) and the previously undescribed whiteite-(CaMnFe) end-members. Mo-Kα CCD intensity data were collected on a twinned crystal of the (CaMnMn)-dominant whiteite and refined in P2/a to wRobs = 0.064 for 1015 observed reflections.

Empirical ferric iron corrections: necessity, assumptions, and effects on selected geothermobarometers

1991 ◽  
Vol 55 (378) ◽  
pp. 3-18 ◽  
Author(s):  
John C. Schumacher
Keyword(s):  
Ferrous Iron ◽  
Ferric Iron ◽  
Bulk Composition ◽  
Total Iron ◽  
Chemical Analyses ◽  
Treatment Results ◽  
Ideal Stoichiometry ◽  
End Members ◽  
Excess Cations ◽  
Mineral Analyses

AbstractThe ferromagnesian silicate minerals, such as garnets, pyroxenes, micas, and amphiboles, appear in a variety of geothermometers and geobarometers. Where complete chemical analyses are available and regardless of bulk composition (metamorphosed pelitic or mafic), the aforementioned minerals commonly contain ferric iron. In mineral analyses using the electron microprobe, ferric and ferrous iron are not distinguished, and all the iron is treated as FeO. In ferric Fe-bearing minerals, this treatment results in (1) low analytical sums and (2) excess cations in the mineral formulae. Assuming ideal stoichiometry (ideal formula cations and oxygens) allows direct ferric estimates in garnets and pyroxenes; amphiboles require additional assumptions concerning site occupancies, and, for micas, no acceptable constraint exists for a ferric estimate. Based on ferric iron determinations for some metamorphic ferromagnesian silicates, the proportion of ferric to total iron increases at higher XMg values. The influence of ferric estimates on T and P calculations depends on the model used and on the extent the ferric estimate alters the relative proportions of end-members. Several examples suggest that, in general, if ferric estimates (or determinations) are made, they should be made for all the relevant minerals.

The formation, preservation and seismic signatures of chemical heterogeneities in the lower mantle

2020 ◽  
Author(s):  
Anna J. P. Gülcher ◽  
Maxim D. Ballmer ◽  
Paul J. Tackley ◽  
Paula Koelemeijer
Keyword(s):  
Physical Properties ◽  
Lower Mantle ◽  
Numerical Models ◽  
Bulk Composition ◽  
Oceanic Lithosphere ◽  
Global Scale ◽  
Seismic Velocities ◽  
Mantle Dynamics ◽  
Wide Range ◽  
Scientific Challenge

<p>Despite stirring by vigorous convection over billions of years, the Earth’s lower mantle appears to be chemically heterogeneous on various length scales. Constraining this heterogeneity is key for assessing Earth’s bulk composition and thermochemical evolution, but remains a scientific challenge that requires cross-disciplinary efforts. On scales below ~1 km, the concept of a “marble cake” mantle has gained wide acceptance, emphasising that recycled oceanic lithosphere, deformed into streaks of depleted and enriched compositions, makes up much of the mantle. On larger scales (10s-100s of km), compositional heterogeneity may be preserved by delayed mixing of this marble cake with either intrinsically-dense or intrinsically-strong materials. Intrinsically dense materials may accumulate as piles at the core-mantle boundary, while intrinsically viscous domains (e.g., enhanced in the strong mineral bridgmanite) may survive as “blobs” in the mid-mantle for large timescales, such as plums in the mantle “plum pudding”<sup>1,2</sup>. While many studies have explored the formation and preservation of either intrinsically-dense (recycled) or intrinsically-strong (primordial) heterogeneity, only few if any have quantified mantle dynamics in the presence of different types of heterogeneity with distinct physical properties.<span> </span></p><p>To address this objective, we use state-of-the-art 2D numerical models of global-scale mantle convection in a spherical-annulus geometry. We explore the effects of the <em>(i)</em> physical properties of primordial material (density, viscosity), <em>(ii)</em> temperature/pressure dependency of viscosity, <em>(iii)</em> lithospheric yielding strength, and <em>(iv)</em> Rayleigh number on mantle dynamics and mixing. Models predict that primordial heterogeneity is preserved in the lower mantle over >4.5 Gyr as discrete blobs for high intrinsic viscosity contrast (>30x) and otherwise for a wide range of parameters. In turn, recycled oceanic crust is preserved in the lower mantle as “marble cake” streaks or piles, particularly in models with a relatively cold and stiff mantle. Importantly, these recycled crustal heterogeneities can co-exist with primordial blobs, with piles often tending to accumulate beneath the primordial domains. This suggests that the modern mantle may be in a hybrid state between the “marble cake” and “plum pudding” styles.<span> </span></p><p>Finally, we put our model predictions in context with recent discoveries from seismology. We calculate synthetic seismic velocities from predicted temperatures and compositions, and compare these synthetics to tomography models, taking into account the limited resolution of seismic tomography. Convection models including preserved bridgmanite-enriched domains along with recycled piles have the potential of reconciling recent seismic observations of lower-mantle heterogeneity<sup>3</sup> with the geochemical record from ocean-island basalts<sup>4,5</sup>, and are therefore relevant for assessing Earth’s bulk composition and long-term evolution.<span> </span></p><p><sup>1</sup> Ballmer et al. (2017), <em>Nat. Geosci</em>., 10.1038/ngeo2898<br><sup>2</sup> Gülcher et al. (in review), <em>EPSL</em>: Variable dynamic styles of primordial heterogeneity preservation in Earth’s lower mantle <br><sup>3</sup> Waszek et al. (2018), <em>Nat. Comm., </em>10.1038/s41467-017-02709-4 <br><sup>4</sup> Hofmann (1997), <em>Nature, </em>10.1038/385219a0; <br><sup>5</sup> Mundl et al. (2017), <em>Science, </em>10.1126/science.aal4179</p>

Origin of anomalous iron meteorites

1979 ◽  
Vol 43 (327) ◽  
pp. 415-421 ◽  
Author(s):  
Edward R. D. Scott
Keyword(s):  
Fractional Crystallization ◽  
Genetic Relationships ◽  
Bulk Composition ◽  
Iron Meteorites ◽  
End Members ◽  
Chemical Groups ◽  
Chemical Trends

SummaryAnomalous iron meteorites are those which do not have Ni, Ga, and Ge contents appropriate to one of the twelve chemical groups; they account for 14% of all irons. The chemistry of irons in the twelve groups can be largely understood in terms of primary fractionation in the nebula, which established the bulk composition of the groups, and secondary fractionation in the parent bodies (probably fractional crystallization), which produced the chemical trends within groups. Logarithmic element-Ga graphs containing data for groups and anomalous irons reveal that anomalous irons experienced the same primary and secondary fractionations as affected the groups.The uniformity of chemical trends within groups allows possible genetic relationships between anomalous irons and groups and among anomalous irons to be tested. It is concluded that the sixty-nine anomalous irons are samples from fifty-odd additional groups, which had similar histories to the twelve groups. Less than five of the anomalous irons could be compositional end- members or reprocessed irons from the groups.Because ‘anomalous’ means abnormal, some other term for the irons which do not belong to the twelve groups would be a useful reminder that these irons formed in a similar way to irons in the major groups. They could be called members of minor groups or grouplets.

scholarly journals The influence of bulk composition on the long-term interior-atmosphere evolution of terrestrial exoplanets

2020 ◽  
Vol 643 ◽  
pp. A44
Author(s):  
Rob J. Spaargaren ◽  
Maxim D. Ballmer ◽  
Dan J. Bower ◽  
Caroline Dorn ◽  
Paul J. Tackley
Keyword(s):  
Plate Tectonics ◽  
Thermal Evolution ◽  
Bulk Composition ◽  
Dynamic Regime ◽  
Evolution Model ◽  
Terrestrial Planets ◽  
Temperature Structure ◽  
Geological Time ◽  
Near Surface

Aims. The secondary atmospheres of terrestrial planets form and evolve as a consequence of interaction with the interior over geological time. We aim to quantify the influence of planetary bulk composition on the interior–atmosphere evolution for Earth-sized terrestrial planets to aid in the interpretation of future observations of terrestrial exoplanet atmospheres. Methods. We used a geochemical model to determine the major-element composition of planetary interiors (MgO, FeO, and SiO2) following the crystallization of a magma ocean after planet formation, predicting a compositional profile of the interior as an initial condition for our long-term thermal evolution model. Our 1D evolution model predicts the pressure–temperature structure of the interior, which we used to evaluate near-surface melt production and subsequent volatile outgassing. Volatiles are exchanged between the interior and atmosphere according to mass conservation. Results. Based on stellar compositions reported in the Hypatia catalog, we predict that about half of rocky exoplanets have a mantle that convects as a single layer (whole-mantle convection), and the other half exhibit double-layered convection due to the presence of a mid-mantle compositional boundary. Double-layered convection is more likely for planets with high bulk planetary Fe-content and low Mg/Si-ratio. We find that planets with low Mg/Si-ratio tend to cool slowly because their mantle viscosity is high. Accordingly, low-Mg/Si planets also tend to lose volatiles swiftly through extensive melting. Moreover, the dynamic regime of the lithosphere (plate tectonics vs. stagnant lid) has a first-order influence on the thermal evolution and volatile cycling. These results suggest that the composition of terrestrial exoplanetary atmospheres can provide information on the dynamic regime of the lithosphere and the thermo-chemical evolution of the interior.

scholarly journals FORest canopy atmosphere transfer (FORCAsT) 1.0: a 1-D model of biosphere–atmosphere chemical exchange

2015 ◽  
Vol 8 (7) ◽  
pp. 5183-5234
Author(s):  
K. Ashworth ◽  
S. H. Chung ◽  
R. J. Griffin ◽  
J. Chen ◽  
R. Forkel ◽  
...  
Keyword(s):  
Gas Phase ◽  
Forest Canopy ◽  
Chemical Exchange ◽  
Critical Role ◽  
Mixed Forest ◽  
Oxidation Products ◽  
Atmospheric Composition ◽  
Alkyl Nitrate ◽  
Key Species ◽  
The Impact

Abstract. Biosphere-atmosphere interactions play a critical role in governing atmospheric composition, mediating the concentration of key species such as ozone and aerosol, thereby influencing air quality and climate. The exchange of reactive trace gases and their oxidation products (both gas and particle phase) is of particular importance in this process. The FORCAsT (FORest Canopy AtmoSphere Transfer) one-dimensional model is developed to study the emission, deposition, chemistry and transport of volatile organic compounds (VOCs) and their oxidation products in the atmosphere within and above the forest canopy. We include an equilibrium partitioning scheme, making FORCAsT one of the few canopy models currently capable of simulating the formation of secondary organic aerosols (SOA) from VOC oxidation in a forest environment. We evaluate the capability of FORCAsT to reproduce observed concentrations of key gas-phase species and report modeled SOA concentrations within and above a mixed forest at the University of Michigan Biological Station (UMBS) during the Community Atmosphere-Biosphere Interactions Experiment (CABINEX) field campaign in summer 2009. We examine the impact of two different gas-phase chemical mechanisms on modelled concentrations of short-lived primary emissions, such as isoprene and monoterpenes, and their oxidation products. While the two chemistry schemes perform similarly under high-NOx conditions, they diverge at the low levels of NOx at UMBS. We identify peroxy radical and alkyl nitrate chemistry as the key causes of the differences, highlighting the importance of this chemistry in understanding the fate of biogenic VOCs (bVOCs) for both the modelling and measurement communities.

scholarly journals Statistics of Double and Multiple Stars in the Solar Neighborhood

1992 ◽  
Vol 135 ◽  
pp. 343-345
Author(s):  
Victor V. Orlov ◽  
Oleg A. Titov
Keyword(s):  
Physical Properties ◽  
Luminosity Function ◽  
Solar Neighborhood ◽  
Solar Neighbourhood ◽  
Stellar Systems ◽  
Additional Peak ◽  
Multiple Stars ◽  
Double And Multiple Stars ◽  
Absolute Magnitudes ◽  
Machine Readable

AbstractWe study the multiplicity function and physical properties of single, double, and multiple stellar systems in the solar neighbourhood (r < 10 pc), using a new preliminary machine–readable version of the Gliese & Jahreiss Catalogue (1991).The ratio of (n+l)-ple to n-ple systems is a constant fraction of about 1/4 for n =1, 2, 3, 4. The luminosity function f(M) for primaries in binaries has an additional peak at M є (6m,8m) that is absent in f(M) for single stars and secondary components. A significant correlation between the absolute magnitudes M1 and M2 of the components in binaries takes place.

Cr-rich Mg-chloritoid, a first record in high-pressure metagabbros from Monviso (Cottian Alps), Italy

1987 ◽  
Vol 51 (363) ◽  
pp. 681-687 ◽  
Author(s):  
J. R. Kienast ◽  
B. Messiga
Keyword(s):  
High Pressure ◽  
Bulk Composition ◽  
First Record ◽  
Alpine Metamorphism ◽  
End Members ◽  
Host Rocks ◽  
Primary Minerals

AbstractMetamorphosed troctolite cumulates occur interbedded with Mg-rich metagabbros in the Monviso ophiolitic massif; they have developed chloritoid, omphacite, talc and garnet during the eclogitic stage of the Eo-alpine metamorphism. The lack of penetrative deformation in the rocks has made it possible to recognize different microstructural sites of chloritoid growth, in which the chloritoid composition may vary widely and is controlled by the specific inherited chemical domain.The chloritoid compositions are unusually rich in Cr and Mg with large variations in Fe2+/Mg and Cr/AlVI ratio. The Cr/Al ratio in chloritoid is linked to both the Cr value of the primary minerals (i.e. Cr-rich spinels, Cr-end-members in the clinopyroxenes) and a limited redistribution of Cr during metamorphism. The Fe2+/Mg ratio, while being partly affected by bulk composition of the host rocks, also varies between different microstructural sites; the highest ratio is recorded in coronas between clinopyroxene and plagioclase, lower values occurring in coronas between plagioclase and olivine.

Potassium isotope composition of Mars reveals a mechanism of planetary volatile retention

2021 ◽  
Vol 118 (39) ◽  
pp. e2101155118
Author(s):  
Zhen Tian ◽  
Tomáš Magna ◽  
James M. D. Day ◽  
Klaus Mezger ◽  
Erik E. Scherer ◽  
...  
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Isotope Composition ◽  
Lower Mass ◽  
Volatile Elements ◽  
Surface Evolution ◽  
Surface Conditions ◽  
Bulk Silicate Earth ◽  
Refractory Elements ◽  
Volatile Loss

The abundances of water and highly to moderately volatile elements in planets are considered critical to mantle convection, surface evolution processes, and habitability. From the first flyby space probes to the more recent “Perseverance” and “Tianwen-1” missions, “follow the water,” and, more broadly, “volatiles,” has been one of the key themes of martian exploration. Ratios of volatiles relative to refractory elements (e.g., K/Th, Rb/Sr) are consistent with a higher volatile content for Mars than for Earth, despite the contrasting present-day surface conditions of those bodies. This study presents K isotope data from a spectrum of martian lithologies as an isotopic tracer for comparing the inventories of highly and moderately volatile elements and compounds of planetary bodies. Here, we show that meteorites from Mars have systematically heavier K isotopic compositions than the bulk silicate Earth, implying a greater loss of K from Mars than from Earth. The average “bulk silicate” δ41K values of Earth, Moon, Mars, and the asteroid 4-Vesta correlate with surface gravity, the Mn/Na “volatility” ratio, and most notably, bulk planet H2O abundance. These relationships indicate that planetary volatile abundances result from variable volatile loss during accretionary growth in which larger mass bodies preferentially retain volatile elements over lower mass objects. There is likely a threshold on the size requirements of rocky (exo)planets to retain enough H2O to enable habitability and plate tectonics, with mass exceeding that of Mars.

Atmosphere composition and N2O emissions in soils of contrasting textures fertilized with anhydrous ammonia

2004 ◽  
Vol 84 (3) ◽  
pp. 339-352 ◽  
Author(s):  
Philippe Rochette, Régis R. Simard ◽  
Noura Ziadi, Michel C. Nolin ◽  
Athyna N. Cambouris
Keyword(s):  
Nitrous Oxide ◽  
Physical Properties ◽  
Water Content ◽  
Soil Physical Properties ◽  
Atmospheric Composition ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions ◽  
N Availability ◽  
Soil N ◽  
Anhydrous Ammonia

Nitrous oxide production and emission in agricultural soils are often influenced by soil physical properties and mineral N content. An experiment was initiated on a commercial farm located in the St. Lawrence Lowlands to measure the effects of recommended (150 kg N ha-1) and excessive (250 kg N ha-1) rates of anhydrous ammonia on atmospheric composition (O2, CO2, CH4 and N2O) and N2O emissions in soils of contrasting textures (sandy loam, clay loam and clay) cropped to corn. N2O emissions and soil temperature, water content and atmospheric composition were measured from post-harvest tillage to the first snowfall during the first year (2000), and from spring thaw to mid-July during the following 2 yr. Episodes of high N2O concentrations and surface emissions coincided with periods of high soil water content shortly following rainfall events when soil O2 concentrations were lowest. The convergence of indicators of restricted soil aeration at the time of highest N2O production suggested that denitrification was a major contributor to N2O emissions even in soils receiving an NH4-based fertilizer. Soil texture had a significant influence on soil N2O concentration and emission rates on several sampling dates. However, the effect was relatively small and it was not consistent, likely because of complex interactions between soil physical properties and N2O production, consumption and diffusion processes. Nitrous oxide emissions during the study were not limited by soil N availability as indicated by similar fluxes at recommended and excessive rates of anhydrous ammonia. Finally, greater N2O emissions in 2001 than in 2002 stress the importance of multiyear studies to evaluate the effect of annual weather conditions on soil N2O dynamics. Key words: Greenhouse gasses, denitrification

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