Abundances Of Refractory Elements Research Articles

Vanadium oxide and a sharp onset of cold-trapping on a giant exoplanet.

The abundance of refractory elements in giant planets can provide key insights into their formation histories1. Owing to the low temperatures of the Solar System giants, refractory elements condense below the cloud deck, limiting sensing capabilities to only highly volatile elements2. Recently, ultra-hot giant exoplanets have allowed for some refractory elements to be measured, showing abundances broadly consistent with the solar nebula with titanium probably condensed out of the photosphere3,4. Here we report precise abundance constraints of 14 major refractory elements on the ultra-hot giant planet WASP-76b that show distinct deviations from proto-solar and a sharp onset in condensation temperature. In particular, we find nickel to be enriched, a possible sign of the accretion of the core of a differentiated object during the evolution of the planet. Elements with condensation temperatures below 1,550 K otherwise closely match those of the Sun5 before sharply transitioning to being strongly depleted above 1,550 K, which is well explained by nightside cold-trapping. We further unambiguously detect vanadium oxide on WASP-76b, a molecule long suggested to drive atmospheric thermal inversions6, and also observe a global east-west asymmetry7 in its absorption signals. Overall, our findings indicate that giant planets have a mostly stellar-like refractory elemental content and suggest that temperature sequences of hot Jupiter spectra can show abrupt transitions wherein a mineral species is either present or completely absent if a cold trap exists below its condensation temperature8.

Quantitative correlation of refractory elemental abundances between rocky exoplanets and their host stars

Context. Stellar elemental abundances are generally used to constrain the interiors of rocky exoplanets by assuming planet’s relative abundances of major refractory elements (Fe, Mg, and Si) are similar to those of their host stars. Very recently, a non-one-to-one correlation was found among the compositions of low-mass planets and their host stars. It is therefore of great interest to further explore this correlation for larger samples of rocky exoplanets. Aims. We focus on a large sample of rocky exoplanets and compute their bulk elemental abundance ratios. We analyze the quantitative correlation between rocky exoplanets and their host stars by comparing the abundance ratios of these refractory elements. Methods. The interior of rocky exoplanets is assumed to be an iron-rich core overlaid with a silicate mantle. We constrained the bulk composition of rocky exoplanets from their measured mass and radius, using Bayesian statistical approaches. Then we used orthogonal distance regression (ODR) to characterize the compositional correlation between rocky exoplanets and their host stars. Results. Some rocky exoplanets are shown to have high iron-mass fractions and are thus likely to be iron-enriched super-Mercuries. We find the iron content of rocky exoplanets is dependent on the metallicity [Fe/H] of their host stars. The planets formed around a higher metallicity star generally span a wider range of iron masses, allowing for a higher iron content. Moreover, we directly compared the iron-mass fractions of rocky exoplanets with those deduced from the refractory elemental abundance ratios of their host stars. The results suggest that most rocky planets are more iron-enriched with respect to the initial protoplanetary disk.

Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants

Relating planet formation to atmospheric composition has been a long-standing goal of the planetary science community. So far, most modeling studies have focused on predicting the enrichment of heavy elements and the C/O ratio in giant planet atmospheres. Although this framework provides useful constraints on the potential formation locations of gas giant exoplanets, carbon and oxygen measurements alone are not enough to determine where a given gas giant planet originated. Here, we show that characterizing the abundances of refractory elements (e.g., silicon and iron) can break these degeneracies. Refractory elements are present in the solid phase throughout most of the disk, and their atmospheric abundances therefore reflect the solid-to-gas accretion ratio during formation. We introduce a new framework that parameterizes the atmospheric abundances of gas giant exoplanets in the form of three ratios: Si/H, O/Si, and C/Si. Si/H traces the solid-to-gas accretion ratio of a planet and is loosely equivalent to earlier notions of “metallicity.” For O/Si and C/Si, we present a global picture of their variation with distance and time based on what we know from the solar system meteorites and an updated understanding of the variations of thermal processing within protoplanetary disks. We show that ultrahot Jupiters are ideal targets for atmospheric characterization studies using this framework as we can measure the abundances of refractories, oxygen, and carbon in the gas phase. Finally, we propose that hot Jupiters with silicate clouds and low water abundances might have accreted their envelopes between the soot line and the water snow line.

Oxygen depletion in giant planets with different formation histories

ABSTRACT The atmospheric C/O ratio of exoplanets is widely used to constrain their formation. To guarantee that the C/O ratio provides robust information, we need to accurately quantify the amount of C and O in exoplanetary atmospheres. In the case of O, water and carbon monoxide are generally studied as the two key carriers. However, oxygen is a very reactive element and does not bind only with carbon; depending on the temperature, it also binds to refractory elements. Estimating the amount of oxygen bound to refractory elements is therefore critical for unbiased estimates of the C/O ratio. In this work, we investigate the oxygen deficit due to refractory elements and its effects on the atmospheric C/O ratio of giant exoplanets as a function of their metallicity and equilibrium temperature. We model the composition of planetary atmospheres assuming chemical equilibrium and using as input physically justified elemental mixtures arising from detailed planet formation simulations. Our results show how the interplay between the atmospheric temperature and non-solar abundances of oxygen and refractory elements can sequester large fractions of oxygen, introducing significant biases in evaluating the C/O ratio when this effect is not accounted for. We apply our results to the case of Jupiter in the Solar system and show how the currently estimated water abundance points to a true oxygen abundance that is four times the solar one.

TOI-1452 b: SPIRou and TESS Reveal a Super-Earth in a Temperate Orbit Transiting an M4 Dwarf

Exploring the properties of exoplanets near or inside the radius valley provides insight on the transition from the rocky super-Earths to the larger, hydrogen-rich atmosphere mini-Neptunes. Here, we report the discovery of TOI-1452b, a transiting super-Earth (R p = 1.67 ± 0.07 R ⊕) in an 11.1 day temperate orbit (T eq = 326 ± 7 K) around the primary member (H = 10.0, T eff = 3185 ± 50 K) of a nearby visual-binary M dwarf. The transits were first detected by the Transiting Exoplanet Survey Satellite, then successfully isolated between the two 3.″2 companions with ground-based photometry from the Observatoire du Mont-Mégantic and MuSCAT3. The planetary nature of TOI-1452b was established through high-precision velocimetry with the near-infrared SPIRou spectropolarimeter as part of the ongoing SPIRou Legacy Survey. The measured planetary mass (4.8 ± 1.3 M ⊕) and inferred bulk density ( g cm−3) is suggestive of a rocky core surrounded by a volatile-rich envelope. More quantitatively, the mass and radius of TOI-1452b, combined with the stellar abundance of refractory elements (Fe, Mg, and Si) measured by SPIRou, is consistent with a core-mass fraction of 18% ± 6% and a water-mass fraction of %. The water world candidate TOI-1452b is a prime target for future atmospheric characterization with JWST, featuring a transmission spectroscopy metric similar to other well-known temperate small planets such as LHS 1140b and K2-18 b. The system is located near Webb’s northern continuous viewing zone, implying that is can be followed at almost any moment of the year.

Inferring the Gas-to-Dust Ratio in the Main Planet-forming Region of Disks

Measuring the amount of gas and dust in protoplanetary disks is a key challenge in planet formation studies. Here we provide a new set of dust depletion factors and relative mass surface densities of gas and dust for the innermost regions of a sample of protoplanetary disks. We do this by combining stellar theory with observed refractory element abundances in both disk hosts and open cluster stars. Our results are independent of, and complementary to, those obtained from spatially resolved disk observations.

Geophysical and cosmochemical evidence for a volatile-rich Mars

Constraints on the composition of Mars principally derive from chemical analyses of a set of Martian meteorites that rely either on determinations of their refractory element abundances or isotopic compositions. Both approaches, however, lead to models of Mars that are unable to self-consistently explain major element chemistry and match its observed geophysical properties, unless ad hoc adjustments to key parameters, namely, bulk Fe/Si ratio, core composition, and/or core size are made. Here, we combine geophysical observations, including high-quality seismic data acquired with the InSight mission, with a cosmochemical model to constrain the composition of Mars. We find that the FeO content of Mars' mantle is 13.7±0.4 wt%, corresponding to a Mg# of 0.81±0.01. Because of the lower FeO content of the mantle, compared with previous estimates, we obtain a higher mean core density of 6150±46 kg/m3 than predicted by recent seismic observations, yet our estimate for the core radius remains consistent around 1840±10 km, corresponding to a core mass fraction of 0.250±0.005. Relying on cosmochemical constraints, volatile element behaviour, and planetary building blocks that match geophysical and isotopic signatures of Martian meteorites, we find that the liquid core is made up of 88.4±3.9 wt% Fe-Ni-Co with light elements making up the rest. To match the mean core density constraint, we predict, based on experimentally-determined thermodynamic solution models, a light element abundance in the range of ≈9 wt% S, ⩾3 wt% C, ⩽2.5 wt% O, and ⩽0.5 wt% H, supporting the notion of a volatile-rich Mars. To accumulate sufficient amounts of these volatile elements, Mars must have formed before the nebular gas dispersed and/or, relative to Earth, accreted a higher proportion of planetesimals from the outer protoplanetary disk where volatiles condensed more readily.

Variable refractory lithophile element compositions of planetary building blocks: Insights from components of enstatite chondrites

Chondrites are sediments of materials left over from the earliest stage of the solar system history. Based on their undifferentiated nature and less fractionated chemical compositions, chondrites are widely considered to represent the unprocessed building blocks of the terrestrial planets and their embryos. Models of chemical composition of the terrestrial planets generally find chondritic relative abundances of refractory lithophile elements (RLE) in the bulk bodies (“constant RLE ratio rule”), based on limited variations of RLE ratios among chondritic meteorites and the solar photosphere. Here, we show that ratios of RLE, such as Nb/Ta, Zr/Hf, Sm/Nd and Al/Ti, are fractionated from the solar value in chondrules from enstatite chondrites (EC). The fractionated RLE ratios of individual EC chondrules document different chalcophile affinities of RLE under highly reducing environments and a separation of RLE-bearing sulfides from silicates before and/or during chondrule formation. In contrast, the bulk EC have solar-like RLE ratios, indicating that a physical sorting of silicates and sulfides was negligible before and during the accretion of EC parent bodies. Likewise, if the Earth’s accretion was dominated by EC-like materials, as supported by multiple isotope systematics, physical sorting of silicates and sulfides in the accretionary disk did not occur. Alternatively, the Earth’s precursors were high-temperature nebular condensates that formed prior to the precipitation of RLE-bearing sulfides. A lack of Ti depletion in the bulk silicate Earth, combined with similar silicate-sulfide and rutile-melt partitioning behaviors of Nb and Ti, prefers a moderately siderophile behavior of Nb as the origin of the accessible Earth’s Nb depletion. Highly reduced planets that have experienced selective removal or accretion of silicates or metal/sulfide phases, such as Mercury, possibly yield fractionated, non-solar bulk RLE ratios.

Tidal pull of the Earth strips the proto-Moon of its volatiles

Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth (Canup, 2004; Ćuk et al., 2016). Despite similarities in the isotopic and chemical abundances of refractory elements compared to Earth's mantle, the Moon is depleted in volatiles (Wolf and Anders, 1980). Current models favour devolatilisation via incomplete condensation of the proto-Moon in an Earth-Moon debris-disk (Charnoz and Michaut, 2015; Canup et al., 2015; Lock et al., 2018). However the physics of this protolunar disk is poorly understood and thermal escape of gas is inhibited by the Earth's strong gravitational field (Nakajima and Stevenson, 2014). Here we investigate a simple process, wherein the Earth's tidal pull promotes intense hydrodynamic escape from the liquid surface of a molten proto-Moon assembling at 3–6 Earth radii. Such tidally-driven atmospheric escape persisting for less than 1 Kyr at temperatures ~1600 − 1700 K reproduces the measured lunar depletion in K and Na, assuming the escape starts just above the liquid surface. These results are also in accord with timescales for the rapid solidification of a plagioclase lid at the surface of a lunar magma ocean (Elkins-Tanton et al., 2011). We find that hydrodynamic escape, both in an adiabatic or isothermal regime, with or without condensation, induces advective transport of gas away from the lunar surface, causing a decrease in the partial pressures of gas species (Ps) with respect to their equilibrium values (Psat). The observed enrichment in heavy stable isotopes of Zn and K (Paniello et al., 2012; Wang and Jacobsen, 2016) constrain Ps/Psat > 0.99, favouring a scenario in which volatile loss occurred at low hydrodynamic wind velocities (<1% of the sound velocity) and thus low temperatures. We conclude that tidally-driven atmospheric escape is an unavoidable consequence of the Moon's assembly under the gravitational influence of the Earth, and provides new pathways toward understanding lunar formation.

Heating events in the nascent solar system recorded by rare earth element isotopic fractionation in refractory inclusions.

Equilibrium condensation of solar gas is often invoked to explain the abundance of refractory elements in planets and meteorites. This is partly motivated, by the observation that the depletions in both the least and most refractory rare earth elements (REEs) in meteoritic group II calcium-aluminum-rich inclusions (CAIs) can be reproduced by thermodynamic models of solar nebula condensation. We measured the isotopic compositions of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb in eight CAIs to test this scenario. Contrary to expectation for equilibrium condensation, we find light isotope enrichment for the most refractory REEs and more subdued isotopic variations for the least refractory REEs. This suggests that group II CAIs formed by a two-stage process involving fast evaporation of preexisting materials, followed by near-equilibrium recondensation. The calculated time scales are consistent with heating in events akin to FU Orionis- or EX Lupi-type outbursts of eruptive pre-main-sequence stars.

Oxygen isotope study of the Asuka-881020 CH chondrite I: Non-porphyritic chondrules

We measured oxygen isotope ratios and major elemental compositions of non-porphyritic chondrules and lithic fragments with various textures and chemical compositions in the Asuka-881020 CH chondrite. The oxygen isotope ratios plot along the primitive chondrule mineral line with Δ17O (=δ17O – 0.52 × δ18O) values from ∼−21‰ to +5‰. The Δ17O values increase with decreasing Mg# (=molar [MgO]/[MgO + FeO]%) from 99.6 to 58.5, similarly to the Δ17O-Mg# trends for the chondrules in other carbonaceous chondrites.Most of the measured objects (non-porphyritic chondrules and lithic fragments) including chondrules analyzed in the previous studies are classified into three groups based on the Δ 17O values and chemistry; the −2.3‰ group with FeO-poor compositions (the most abundant group), the +1.4‰ group with FeO-rich compositions, and the −6.3‰ group with FeO-poor compositions. Skeletal olivine and magnesian cryptocrystalline (MgCC) chondrules and MgCC chondrule fragments, which are the −2.3‰ group objects, may have formed via fractional condensation in the isotopically uniform gaseous environment with Δ 17O of −2.3‰. When silica-normative materials condensed from gas at ∼1200 K, 16O-rich refractory solids, similar to Ca-Al-rich inclusions, were incorporated into the environment. The silica-normative materials that condensed onto the 16O-rich refractory solids were reheated at 1743–1968 K and formed cristobalite-bearing chondrules with Δ17O of ∼−6‰. This scenario can explain the absence of silica-bearing chondrules in the −2.3‰ group and refractory element abundances in the cristobalite-bearing chondrules as high as those in the MgCC chondrules.Refractory element abundances of the +1.4‰ group objects decrease from FeO-Al-rich and ferroan CC (FeCC) chondrules to FeCC chondrule fragments to FeNi metal-bearing to silica-bearing chondrules. This suggests the formation via fractional condensation in the isotopically uniform gaseous environment. The Δ17O values and FeO-rich compositions of this group could be explained by an addition of 16O-poor water ice as an oxidant to the relatively 16O-rich solids with Δ17O of −2.3‰, which may also explain existence of some MgCC chondrules and fragments with intermediate Δ17O values between −2.3‰ and +1.4‰. The immiscibility textures in the silica-bearing chondrules suggest a reheating event at a temperature of >1968 K after condensation of silica-normative materials. Thus, the non-porphyritic chondrules and fragments in CH and CB chondrites, which are classified into three distinct Δ17O groups, require multiple chondrule-forming environments and heating events. Energy source for the heating events could be either impact plume and/or other dynamical processes in the protoplanetary disk, though a single heating event would not fully explain observed chemical and isotope signatures in these non-porphyritic chondrules.

The composition of Mars

Comparing compositional models of the terrestrial planets provides insights into physicochemical processes that produced planet-scale similarities and differences. The widely accepted compositional model for Mars assumes Mn and more refractory elements are in CI chondrite proportions in the planet, including Fe, Mg, and Si, which along with O make up >90% of the mass of Mars. However, recent improvements in our understandings on the composition of the solar photosphere and meteorites challenge the use of CI chondrite as an analog of Mars. Here we present an alternative model composition for Mars that avoids such an assumption and is based on data from Martian meteorites and spacecraft observations. Our modeling method was previously applied to predict the Earth’s composition. The model establishes the absolute abundances of refractory lithophile elements in the bulk silicate Mars (BSM) at 2.26 times higher than that in CI carbonaceous chondrites. Relative to this chondritic composition, Mars has a systematic depletion in moderately volatile lithophile elements as a function of their condensation temperatures. Given this finding, we constrain the abundances of siderophile and chalcophile elements in the bulk Mars and its core. The Martian volatility trend is consistent with ⩽7 wt% S in its core, which is significantly lower than that assumed in most core models (i.e., >10 wt% S). Furthermore, the occurrence of ringwoodite at the Martian core-mantle boundary might have contributed to the partitioning of O and H into the Martian core.

The Chemical Signatures of Planetary Engulfment Events in Binary Systems

Abstract Planetary engulfment events involve the chemical assimilation of a planet into a star’s external layer. This can cause a change in the chemical pattern of the stellar atmosphere in a way that mirrors the composition of the rocky object engulfed, with the refractory elements being more abundant than the volatiles. Due to these stellar chemical changes, planetary engulfment events can render the process of chemical tagging potentially inaccurate. A line-by-line differential analysis of twin stars in wide binary systems allows us to test the chemical homogeneity of these associations with typical individual stellar Fe i uncertainties of 0.01 dex and eventually unveil chemical anomalies that could be attributed to planetary engulfment events. Out of the 14 systems analyzed here, we report the discovery of the most chemically inhomogeneous system to date (HIP 34407/HIP 34426). The median difference in abundances of refractory elements within the pair is 0.19 dex and the trend between the differential abundances and condensation temperature suggests that the anomaly is likely due to a planetary engulfment event. Within our sample, five other chemically anomalous systems are found.

New Solar Metallicity Measurements

In the past years, a systematic downward revision of the metallicity of the Sun has led to the “solar modeling problem”, namely the disagreement between predictions of standard solar models and inferences from helioseismology. Recent solar wind measurements of the metallicity of the Sun, however, provide once more an indication of a high-metallicity Sun. Because of the effects of possible residual fractionation, the derived value of the metallicity Z ⊙ = 0 . 0196 ± 0 . 0014 actually represents a lower limit to the true metallicity of the Sun. However, when compared with helioseismological measurements, solar models computed using these new abundances fail to restore agreement, owing to the implausibly high abundance of refractory (Mg, Si, S, Fe) elements, which correlates with a higher core temperature and hence an overproduction of solar neutrinos. Moreover, the robustness of these measurements is challenged by possible first ionization potential fractionation processes. I will discuss these solar wind measurements, which leave the “solar modeling problem” unsolved.

HD 219666 b: a hot-Neptune from TESS Sector 1

We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD 219666 (M⋆ = 0.92 ± 0.03 M⊙, R⋆ = 1.03 ± 0.03 R⊙, τ⋆ = 10 ± 2 Gyr). With a mass of Mb = 16.6 ± 1.3 M⊕, a radius of Rb = 4.71 ± 0.17 R⊕, and an orbital period of Porb ≃ 6 days, HD 219666 b is a new member of a rare class of exoplanets: the hot-Neptunes. The Transiting Exoplanet Survey Satellite (TESS) observed HD 219666 (also known as TOI-118) in its Sector 1 and the light curve shows four transit-like events, equally spaced in time. We confirmed the planetary nature of the candidate by gathering precise radial-velocity measurements with the High Accuracy Radial velocity Planet Searcher (HARPS) at ESO 3.6 m. We used the co-added HARPS spectrum to derive the host star fundamental parameters (Teff = 5527 ± 65 K, log g⋆ = 4.40 ± 0.11 (cgs), [Fe/H]= 0.04 ± 0.04 dex, log R′HK = −5.07 ± 0.03), as well as the abundances of many volatile and refractory elements. The host star brightness (V = 9.9) makes it suitable for further characterisation by means of in-transit spectroscopy. The determination of the planet orbital obliquity, along with the atmosphericmetal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.

Evolution of the Dust Composition in Damped Lyα Systems

Abstract We present a method for estimating the relative abundances of refractory elements in the interstellar dust of galaxies hosting damped Lyα (DLA) systems. The method requires gas-phase column densities of volatile and refractory elements, obtained from absorption-line spectroscopy, and interstellar abundances of the same elements, predicted by chemical evolution models of DLA galaxies. We applied this method to the sample of DLA systems with measurements of Mg, Si, S, Fe, and Zn column densities. We find that the dust abundance ratios (Si/Fe)d and (Mg/Fe)d decrease by almost two orders of magnitude in the metallicity range between ≃1/100 solar to roughly solar. This decrease is stronger than the well-known decline of α/Fe ratios with metallicity observed in metal-poor stars and galaxies, suggesting the existence of metallicity-dependent mechanisms of dust production. To cast light on these mechanisms we investigated the contributions of different stellar sources and interstellar processes to the galactic cycle of dust. We find that Type II SNe are important contributors to the dust composition at low metallicity ([Fe/H] &lt; −0.6), whereas dust accretion in the interstellar medium appears to be important at higher metallicities, leading to a gradual rise of iron-rich particles, possibly in metal form. To further investigate the nature of the dust, we introduced an idealized model of dust grains based on a mixture of silicates (pyroxenes and olivines) and an iron-rich constituent. The model reproduces the evolutionary trends and suggests that olivines are dominant in silicates, in line with other studies of interstellar dust composition.

Thermo-chemical constraints on the lunar bulk composition and the structure of a three-layer mantle

The main purpose of the present study is to evaluate the lunar bulk composition (BSM) and the composition of a three-layer mantle based on a joint inversion of lunar mass and moment of inertia, and the mantle seismic velocity profiles in combination with Gibbs free energy minimization. As an integral characteristic of the thermal state, the mean volume temperature Tmean of the lunar mantle controlling the mineral composition of the Moon was chosen. In terms of Tmean, all thermal models can be conditionally divided into “cold” ones with Tmean ∼ 690–860 °C and “hot” ones with Tmean ∼ 925–1075 °C. We find that irrespective of the thermal state, BSM is characterized by practically constant values of bulk FeO ∼ 12–13 wt% and Mg# 80–81.5, which indicates a significant difference in the composition of the silicate Earth (BSE) and its satellite. The FeO content of 11–14 wt% and Mg# 80–83 are approximately identical in the upper and lower mantle. The bulk SiO2 abundance depends little on the thermal state and ranges from 45 to 52 wt%, with probable concentrations of SiO2 being 50–55% in the upper mantle and 45–50 wt% in the lower mantle; orthopyroxene, and not olivine, is the predominant mineral of the upper mantle. On the contrary, the lunar abundance of alumina, depending on the thermal state, falls into two different groups. Cold models of BSM with a content of 3–4.6 wt% Al2O3 are comparable to those of BSE, whereas for hot models the bulk-alumina content can be in the range of 1.2–1.7 × BSE. The results indicate a tendency for a gradual increase in the alumina content with depth: from 1 to 2% in the upper mantle to 4–7 wt% Al2O3 in the lower mantle with an increasing amount of garnet. The composition of the middle mantle remains controversial, since it may partially overlap with the compositions of the overlying and underlying shells. Our simulation results show that a chemically stratified lunar interior is consistent with the observations and has similar concentrations of FeO and MgO but different concentrations of Al2O3 and SiO2 in different zones of the mantle. However, the question of the similarity and/or difference in the composition of the silicate Earth and its satellite with respect to the abundance of refractory elements, which is of fundamental importance for lunar geochemistry, remains unresolved and requires further research.

Geochemical Constraints on the Cold and Hot Models of the Moon’s Interior: 1–Bulk Composition

The variations of the bulk composition of the silicate Moon (crust + mantle = Bulk Silicate Moon, BSM) depending on the thermal state are explored based on the joint inversion of gravitational, seismic, and petrologic data within the Na2O–TiO2–CaO–FeO–MgO–Al2O3–SiO2 system. The mantle bulk temperature Tmean determining the mineral composition and physical properties of the Moon is adopted as the integral characteristic of thermal state. By parameter Tmean, all thermal models of the Moon can be conventionally broken down into the “cold” with Tmean ~ 690–860°C and the “hot” with Tmean ~ 925–1075°C. The estimations of refractory oxide abundance in lunar rocks depending on the thermal state are included in two different groups. Cold models of BSM are comparable by the bulk content of Al2O3 ~ 3.0–4.6 wt % to those for the silicate Earth (Bulk Silicate Earth, BSE), while hot models of BSM are significantly enriched with Al2O3 ~ 5.1–7.3 wt % (Al2O3 ~ 1.2–1.7 × BSE) as compared with BSE. On the contrary, independent of the temperature distribution, both types of BSM models are characterized by nearly constant values of bulk concentrations of FeO ~ 12–13 wt % and magnesian number MG# 80–81.5 (MG# = [MgO/(MgO + FeO) × 100]), which differ markedly from those for BSE (FeO ~ 8% and MG# 89). It means that for all possible temperature distributions, the silicate fraction of the Moon is FeO-enriched and MgO-depleted in relation to BSE. These arguments discard the possibility of the Moon’s formation out of the material of the Earth’s primitive mantle. In spite of the almost complete coincidence of the isotopic systems, this apparently undeniable fact has no adequate explanation in the existing canonical models of the Moon’s origin and should result in additional constraints on the dynamic processes in models of the formation of the Earth–Moon system. However, the problem of the similarity of and/or difference between compositions of the Moon and the Earth regarding the abundance of refractory elements, which is very important for the geochemistry of the Moon and the Earth’s mantle, remains unresolved and requires further study.

The Effect of Jupiter's Formation on the Distribution of Refractory Elements and Inclusions in Meteorites

We present a comprehensive evolutionary model of the Sun's protoplanetary disk, constructed to resolve the "CAI Storage" problem of meteoritics. We predict the abundances of calcium-rich, aluminum-rich inclusions (CAIs) and refractory lithophile elements under the central assumption that Jupiter's $\sim 30 \, M_{\oplus}$ core forms at about 3 AU at around 0.6 Myr and opened a gap CAIs are trapped in the pressure maximum beyond Jupiter; carbonaceous chondrites formed there. Inside Jupiter's orbit, CAIs were depleted by aerodynamic drag; ordinary and enstatite chondrites formed there. For 16 chondrites and achondrites, we review meteoritic data on their CAI and refractory abundances and their times of formation, constrained by radiometric dating and thermal models. We predict their formation locations, finding excellent consistency with other location information (water content, asteroid spectra and parent bodies). We predict the size of particle concentrated by turbulence for each chondrite, finding excellent matches to each chondrites's mean chondrule diameter. These consistencies imply meteorite parent bodies assembled quickly from local materials concentrated by turbulence, and usually did not migrate far. We predict CI chondrites are depleted in refractory lithophile elements relative to the Sun, by about 12% (0.06 dex). We constrain the variation of turbulence parameter $\alpha$ in the disk, and find a limited role for magnetorotational instability, favoring hydrodynamical instabilities in the outer disk, plus magnetic disk winds in the inner disk. Between 3 and 4 Myr at least, gas persisted outside Jupiter but was depleted inside it, and the solar nebula was a transition disk.

Mass, Radius, and Composition of the Transiting Planet 55 Cnc e: Using Interferometry and Correlations

Abstract The characterization of exoplanets relies on that of their host star. However, stellar evolution models cannot always be used to derive the mass and radius of individual stars, because many stellar internal parameters are poorly constrained. Here, we use the probability density functions (PDFs) of directly measured parameters to derive the joint PDF of the stellar and planetary mass and radius. Because combining the density and radius of the star is our most reliable way of determining its mass, we find that the stellar (respectively planetary) mass and radius are strongly (respectively moderately) correlated. We then use a generalized Bayesian inference analysis to characterize the possible interiors of 55 Cnc e. We quantify how our ability to constrain the interior improves by accounting for correlation. The information content of the mass–radius correlation is also compared with refractory element abundance constraints. We provide posterior distributions for all interior parameters of interest. Given all available data, we find that the radius of the gaseous envelope is . A stronger correlation between the planetary mass and radius (potentially provided by a better estimate of the transit depth) would significantly improve interior characterization and reduce drastically the uncertainty on the gas envelope properties.