Building Blocks Of Planets Research Articles

Superconductivity in Dilute Hydrides of Ammonia under Pressure.

The past decade has witnessed great progress in predicting and synthesizing polyhydrides that exhibit superconductivity under pressure. Dopants allow these compounds to become metals at pressures lower than those required to metallize elemental hydrogen. Here, we show that by combining the fundamental planetary building blocks of molecular hydrogen and ammonia, conventional superconducting compounds can be formed at high pressure. Through extensive theoretical calculations, we predict metallic metastable structures with NHn (n = 10, 11, 24) stoichiometries that are based on NH4+ superalkali cations and complex hydrogenic lattices. The hydrogen atoms in the molecular cation contribute to the superconducting mechanism, and the estimated superconducting critical temperatures, Tc's, are comparable to the highest values computed for the alkali metal polyhydrides. The largest calculated (isotropic Eliashberg) Tc is ∼180 K for Pnma-NH10 at 300 GPa. Our results suggest that other molecular cations can be mixed with hydrogen under pressure, yielding superconducting compounds.

Evaluations Using Clouds of Tiny Cosmic Dust Particles

We talked about the existence of cosmic dust particles in this article, which are composed of different elements like carbon, oxygen, iron, and other atoms heavier than hydrogen and helium. Star formation depends on cosmic dust particles, which are the building blocks of planets and people. Dust that has fallen to Earth or exists in space is known as cosmic dust, sometimes known as extraterrestrial dust or space dust. The majority of particles of cosmic dust have sizes between a few molecules and 0.1 mm (100 µm). We refer to larger particles as meteorites. Cosmic dust is thought to be the remnants of asteroidal or cometary collisions that can be linked to collisions that took place during the Big Bang.

The H-poor nature of incompletely melted planetesimals: The view from acapulcoites and lodranites

The abundance of H in planetary building blocks is of fundamental importance for constraining the evolution of the terrestrial planets. It is commonly assumed that chondrites are the principal sources of Earth’s H; however, recent studies have suggested that primitive achondrites and achondrites may retain a small complement of H. There are few constraints on the H budgets of primitive achondrites, which represent the transition from unmelted to melted planetesimals, but prior work suggests that bulk parent body H contents are several orders of magnitude lower than typical chondritic values. Therefore, to provide further constraints on H retention during the transition from unmelted to melted planetesimals, we have measured the H contents of olivine, orthopyroxene, clinopyroxene, and plagioclase from a suite of acapulcoite-lodranite clan meteorites. Acapulcoite-lodranite clan meteorites represent the “prototypical” primitive achondrite parent body and have bulk major element compositions more akin to the Earth than previously studied primitive achondrites (e.g., the ureilites). We find that the H2O contents of olivine (∼5–12 µg/g H2O), orthopyroxene (∼3–10 µg/g H2O), and clinopyroxene (∼5–8 µg/g H2O) are broadly similar, while plagioclase (∼2.5–5 µg/g H2O) tends to be offset to lower values. Using a simple, single-stage batch-melting model, we calculate a preferred maximum acapulcoite-lodranite parent body H2O content of 38 µg/g, which is similar to other estimates for primitive achondritic and achondritic parent bodies. Furthermore, assuming chondrite-like precursor materials, our data are consistent with efficient loss of H prior to or during the onset of melting of early-formed planetesimals. This requires that Earth’s H-budget was dominated by building blocks that underwent minimal thermal processing.

Identification of a 4.3 billion year old asteroid family and planetesimal population in the Inner Main Belt

Context. Understanding the conditions that lead to the formation of planetesimals – the building blocks of planets - and their initial size distribution is a central problem of modern planetology. While most of these original planetesimals were accreted onto the terrestrial planets and the cores of the giant planets, some were also stranded in the main belt, where 4.5 Gyr of collisional evolution broke most of them into families of collisional asteroid fragments. However, some planetesimals survived, and are still hidden amongst asteroid fragments in the main belt. Aims. We make use of astronomical data to identify these leftover planetesimals amongst all other asteroids. Our search is based on separating planetesimal survivors from families of asteroids generated by collisions. Namely, we aim to identify and “clean” the main belt of collisional family members: by doing so, we would be left with the surviving members of the original planetesimals. Methods. We focus here on the inner portion of the main belt for asteroids with intermediate to high albedo. It is known that current asteroid family catalogs are not suitable for the aforementioned cleaning; they are conservative and only one-quarter of the known asteroids are associated with the approximately 120 distinct asteroid families. We therefore developed methods to inclusively link asteroids to known collisional families in order to better capture their extent. Namely, we apply a hierarchical clustering method (HCM) on asteroids filtered according to the V-shape of the Yarkovsky drift of each family in order to reassess family membership (V-shape-constrained HCM). The identified families were removed and the remaining background population was searched for previously undetected collisional families. Results. We succeed in using our V-shape-constrained HCM to link family “halos” to their cores. After removing these reassessed families from the asteroid population, our V-shape search reveals a previously unknown collisional family of S-type asteroids in the inner main belt with an age of 4.3 ± 1.7 Gyr and a significance level of 3.4σ. When this ancient collisional family is removed, 34 planetesimals are identified and their size-frequency distribution is presented. Conclusions. The asteroid belt has two components: planetesimals and collisional fragments. The cumulative size-frequency distribution of planetesimals has a steep power-law index for bodies larger than 100 km in diameter and a much smaller power-law index for planetesimals smaller than 100 km.

Silicon isotope constraints on terrestrial planet accretion

Understanding the nature and origin of the precursor material to terrestrial planets is key to deciphering the mechanisms and timescales of planet formation1. Nucleosynthetic variability among rocky Solar System bodies can trace the composition of planetary building blocks2–5. Here we report the nucleosynthetic composition of silicon (μ30Si), the most abundant refractory planet-building element, in primitive and differentiated meteorites to identify terrestrial planet precursors. Inner Solar System differentiated bodies, including Mars, record μ30Si deficits of −11.0 ± 3.2 parts per million to −5.8 ± 3.0 parts per million whereas non-carbonaceous and carbonaceous chondrites show μ30Si excesses from 7.4 ± 4.3 parts per million to 32.8 ± 2.0 parts per million relative to Earth. This establishes that chondritic bodies are not planetary building blocks. Rather, material akin to early-formed differentiated asteroids must represent a major planetary constituent. The μ30Si values of asteroidal bodies correlate with their accretion ages, reflecting progressive admixing of a μ30Si-rich outer Solar System material to an initially μ30Si-poor inner disk. Mars’ formation before chondrite parent bodies is necessary to avoid incorporation of μ30Si-rich material. In contrast, Earth’s μ30Si composition necessitates admixing of 26 ± 9 per cent of μ30Si-rich outer Solar System material to its precursors. The μ30Si compositions of Mars and proto-Earth are consistent with their rapid formation by collisional growth and pebble accretion less than three million years after Solar System formation. Finally, Earth’s nucleosynthetic composition for s-process sensitive (molybdenum and zirconium) and siderophile (nickel) tracers are consistent with pebble accretion when volatility-driven processes during accretion and the Moon-forming impact are carefully evaluated.

How the origin of stars in the Galaxy impacts the composition of planetary building blocks

Context. Our Galaxy is composed of different stellar populations with varying chemical abundances, which are thought to imprint the composition of planet building blocks (PBBs). As such, the properties of stars should affect the properties of planets and small bodies formed in their systems. In this context, high-resolution spectroscopic surveys open a window into the chemical links between and their host stars. Aims. We aim to determine the PBB composition trends for various stellar populations across the Galaxy by comparing the two large spectroscopic surveys APOGEE and GALAH. We assess the reliability of the PBB composition as determined with these surveys with a propagation error study. Methods. Stellar spectroscopic abundances from the large surveys GALAH-DR3 and APOGEE-DR17 were used as input with a stoichiometric condensation model. We classified stars into different Galactic components and we quantified the PBB composition trends as a function of [Fe/H]. We also analysed the distribution composition patterns in the [α/Fe]–[Fe/H] diagram. Results. Our propagation error study suggests that the overall trends with [Fe/H] and [α/Fe] are robust, which is supported by the double study of both APOGEE and GALAH. We therefore confirm the existence of a bimodal PBB composition separating the thin disc stars from the thick disc stars. Furthermore, we confirm that the stoichiometric water PBB content is anti-correlated with [Fe/H]. Conclusions. Our results imply that metal-poor stars both in the thin and thick disks are suitable hosts for water-rich PBBs and for ice-rich small bodies. However, for metal-poor stars ([Fe/H]<0), the PBBs around thick disc stars should have a higher water content than that around thin disc stars because of the α-content dependence of the water mass fraction. Given the importance of the initial water abundance of the PBBs in recent planet formation simulations, we expect that the star origin influences the exoplanet population properties across the Galaxy.

Stirred but not shaken: a multiwavelength view of HD 16743’s debris disc

ABSTRACT Planetesimals – asteroids and comets – are the building blocks of planets in protoplanetary discs and the source of dust, ice, and gas in debris discs. Along with planets they comprise the left-over material after star formation that constitutes a planetary system. Planets influence the dynamics of planetesimals, sculpting the orbits of debris belts to produce asymmetries or gaps. We can constrain the architecture of planetary systems, and infer the presence of unseen planetary companions, by high spatial resolution imaging of debris discs. HD 16743 is a relatively young F-type star that hosts a bright edge-on debris disc. Based on far-infrared Herschel observations its disc was thought to be stirred by a planetary companion. Here, we present the first spatially resolved observations at near-infrared and millimetre wavelengths with HST and ALMA, revealing the disc to be highly inclined at $87{_{.}^{\circ}} 3~^{+1{_{.}^{\circ}} 9}_{-2{_{.}^{\circ}} 5}$ with a radial extent of 157.7$^{+2.6}_{-1.5}$ au and an full width at half maximum of 79.4$^{+8.1}_{-7.8}$ au (ΔR/R = 0.5). The vertical scale height of the disc is 0.13 ± 0.02, significantly greater than typically assumed unstirred value of 0.05, and could be indicative of stirring of the dust-producing planetesimals within the disc by bodies at least a few times the mass of Pluto up to 18.3 M⊕ in the single object limit.

Origin of life-forming volatile elements in the inner Solar System.

Volatile elements such as hydrogen, carbon, nitrogen and oxygen are essential ingredients to build habitable worlds like Earth, but their origin and evolution on terrestrial planets remain highly debated. Here we discuss the processes that distributed these elements throughout the early Solar System and how they then became incorporated into planetary building blocks. Volatiles on Earth and the other terrestrial planets appear to have been heterogeneously sourced from different Solar System reservoirs. The sources of planetary volatiles and the timing at which they were accreted to growing planets probably play a crucial role in controlling planet habitability.

Stumbling over Planetary Building Blocks: AU Microscopii as an Example of the Challenge of Retrieving Debris-disk Dust Properties

We explore whether assumptions about dust grain shape affect the resulting estimates of the composition and grain size distribution of the AU Microscopii (AU Mic) debris disk from scattered-light data collected by Lomax et al. The near edge-on orientation of the AU Mic debris disk makes it ideal for studying the effect of the scattering phase function on the measured flux ratios as a function of wavelength and projected distance. Previous efforts to model the AU Mic debris disk have invoked a variety of dust grain compositions and explored the effect of porosity, but did not undertake a systematic effort to explore a full range of size distributions and compositions to understand possible degeneracies in fitting the data. The degree to which modeling dust grains with more realistic shapes compounds these degeneracies has also not previously been explored. We find differences in the grain properties retrieved depending on the grain shape model used. We also present here our calculations of porous grains of size parameters x = 0.1 to 48 and complex refractive indices (m = n + iκ) ranging from n = 1.1 to 2.43 and k = 0 to 1.0, covering multiple compositions at visible and near-infrared wavelengths such as ice, silicates, amorphous carbon, and tholins.

Forming Planets Around Stars With Non-Solar Elemental Composition

Context. Stars in the solar neighbourhood have refractory element ratios slightly different from that of the Sun. It is unclear how much the condensation of solids and thus the composition of planets forming around these stars is affected. Aims. We aim to understand the impact of changing the ratios of the refractory elements Mg, Si, and Fe within the range observed in solar-type stars within 150 pc of the Sun on the composition of planets forming around them. Methods. We use the GGchem code to simulate the condensation of solids in protoplanetary disks with a minimum mass solar nebula around main sequence G-type stars in the solar neighbourhood. We extract the stellar elemental composition from the Hypatia Database. Results. We find that a lower Mg/Si ratio shifts the condensation sequence from forsterite (Mg2SiO4) and SiO to enstatite (MgSiO3) and quartz (SiO2); a lower Fe/S ratio leads to the formation of FeS and FeS2 and few or no Fe-bearing silicates. Ratios of refractory elements translate directly from the gas phase to the condensed phase for T < 1000 K. However, ratios with respect to volatile elements (e.g. oxygen and sulphur) in the condensates – the building blocks of planets – differ from the original stellar composition. Conclusions. Our study shows that the composition of planets crucially depends on the abundances of the stellar system under investigation. Our results can have important implications for planet interiors, which depend strongly on the degree of oxidation and the sulphur abundance.

Imprint of chondrule formation on the K and Rb isotopic compositions of carbonaceous meteorites.

Chondrites display isotopic variations for moderately volatile elements, the origin of which is uncertain and could have involved evaporation/condensation processes in the protoplanetary disk, incomplete mixing of the products of stellar nucleosynthesis, or aqueous alteration on parent bodies. Here, we report high-precision K and Rb isotopic data of carbonaceous chondrites, providing new insights into the cause of these isotopic variations. We find that the K and Rb isotopic compositions of carbonaceous chondrites correlate with their abundance depletions, the fractions of matrix material, and previously measured Te and Zn isotopic compositions. These correlations are best explained by the variable contribution of chondrules that experienced incomplete condensation from a supersaturated medium. From the data, we calculate an average chondrule cooling rate of ~560 ± 180 K/hour, which agrees with values constrained from chondrule textures and could be produced in shocks induced by nebular gravitational instability or motion of large planetesimals through the nebula.

Calcium isotope cosmochemistry

The past decade has seen significant advancements in analytical capabilities and with it a marked increase in the use of Ca isotopes to advance our understanding of the Solar System's and Earth's evolution. Here, mass-dependent and non-mass-dependent Ca isotopic variations in bulk meteorites and chondrite components are discussed. This contribution also examines how Ca isotopes record nebular processes, including evaporation/condensation and mixing of chemically and isotopically distinct reservoirs in the protoplanetary disk. The applicability of non-mass-dependent Ca isotopic variations to tracing the nature and timing of stellar mass contributions to the parental molecular cloud is discussed. This includes the constraints Ca isotopic data provide on the nature of and the relationships between planetary building blocks. This contribution also explores the effects of parent body-based and terrestrial secondary processes, and variable sampling of isotopically heterogeneous Ca-rich components, on bulk meteorite compositions. Using the data reviewed here, this contribution attempts to reconcile the chemical and isotopic Ca data from bulk meteorites and meteorite components to address a major goal in planetary science, the development of a comprehensive model of the chemical and isotopic evolution of the Solar nebula into our planetary system.

Accretion and differentiation of early planetary bodies as recorded in the composition of the silicate Earth

The abundances of the chemical elements and radiogenic isotopes in the silicate Earth provide key information on the composition of planetary building blocks, the accretion process, including its timing, and the early planetary-wide chemical differentiation. The abundances of the lithophile and highly siderophile elements in the bulk silicate Earth can be modeled as a mixture of three distinct components. Component A (proto-Earth) consisted of volatile element-depleted and strongly reduced material to which a highly oxidized component B (impactor, Theia) was added with chondritic element abundances for the refractory elements to slightly depleted in the volatile elements. Finally, a late veneer (component C) added more material with a composition similar to carbonaceous chondrites. These components make up ~85%, ~15% and ~0.4% of the mass of the silicate Earth, respectively. The sequence of their accretion led to a first core formation that produced a metallic core and depleted the silicate portion in siderophile elements including most of the Fe. Addition of the oxidized and volatile richer component B was followed by a second core formation event with removal of a sulfide melt and depletion of the mantle in chalcophile and siderophile elements. The final addition of a late chondritic veneer established a near CI-chondritic abundance among the highly siderophile elements, but also among S, Se and Te. The significant chemical differences between the two first and major components imply that they formed in different regions of the solar system and from isotopically distinct material. The homogeneity of the isotope ratios of refractory elements in the Earth-Moon system then requires a giant impact that was energetic enough to homogenize the material from the two bodies. The combination of the two major components that formed the Earth is contemporaneous with the formation of the Moon. The initial Sr-isotope composition of the Moon indicates that this impact occurred at 4.507 (15) Ga. The most-likely major source for the highly volatile elements, including water on Earth, is the Moon-forming impactor. Thus, the habitability of Earth and its ability to develop plate tectonic processes is the result of the chance collision of proto-Earth with a planetary body that had formed dominantly from material originating beyond the orbit where Earth formed and therefore had accreted a higher amount of volatile elements.

Composition of terrestrial exoplanet atmospheres from meteorite outgassing experiments

Terrestrial exoplanets likely form initial atmospheres through outgassing during and after accretion, although there is currently no first-principles understanding of how to connect a planet's bulk composition to its early atmospheric properties. Important insights into this connection can be gained by assaying meteorites, representative samples of planetary building blocks. We perform laboratory outgassing experiments that use a mass spectrometer to measure the abundances of volatiles released when meteorite samples are heated to 1200 $^{\circ}$C. We find that outgassing from three carbonaceous chondrite samples consistently produce H$_2$O-rich (averaged ~66 %) atmospheres but with significant amounts of CO (~18 %) and CO$_2$ (~15 %) as well as smaller quantities of H$_2$ and H$_2$S (up to 1 %). These results provide experimental constraints on the initial chemical composition in theoretical models of terrestrial planet atmospheres, supplying abundances for principal gas species as a function of temperature.

Maximum temperatures in evolving protoplanetary discs and composition of planetary building blocks

ABSTRACT The maximum temperature and radial temperature profile in a protoplanetary disc are important for the condensation of different elements in the disc. We simulate the evolution of a set of protoplanetary discs from the collapse of their progenitor molecular cloud cores as well as the dust decoupling within the discs as they evolve. We show how the initial properties of the cloud cores affect the thermal history of the protoplanetary discs using a simple viscous disc model. Our results show that the maximum mid-plane temperature in the disc occurs within 0.5 au. It increases with the initial cloud temperature and decreases with its angular velocity and the viscosity of the disc. From the observed properties of the molecular cloud cores, we find the median value of the maximum temperature is around 1250 K, with roughly 90 per cent of them being less than 1500 K – a value that is lower than the 50 per cent condensation temperatures of most refractory elements. Therefore, only cloud cores with high initial temperatures or low-angular velocities and/or low viscosities within the planet-forming discs will result in refractory-rich planetesimals. To reproduce the volatile depletion pattern of CM, CO, and CV chondrites and the terrestrial planets in Solar system, one must either have rare properties of the initial molecular cloud cores like high core temperature, or other sources of energy to heat the disc to sufficiently high temperatures. Alternatively, the volatile depletion observed in these chondrites may be inherited from the progenitor molecular cloud.

A search for trends in spatially resolved debris discs at far-infrared wavelengths

ABSTRACT Debris discs around main-sequence stars are belts of planetesimals – asteroids and comets – formed in the protoplanetary discs around young stars. Planetesimals comprise both the building blocks of planets around young stars and the source of dusty debris around older stars. Imaging observations of dust continuum emission and scattered light reveal the location of these planetesimal belts around their host stars. Analysis of debris discs observed at millimetre wavelengths revealed a trend between the discs’ radii and the host star luminosities. This trend was tentatively linked to the preferential formation of dust-producing planetesimals near snow lines (specifically CO) in the protoplanetary discs around the host stars. Here, we perform a homogeneous analysis of 95 debris discs observed at far-infrared wavelengths by the Herschel Space Observatory and fit the obtained distribution of radii and widths as a function of stellar luminosity with a power-law relation. We identify a trend in disc radius as a function of stellar luminosity similar to that identified at millimetre wavelengths, but cannot convincingly recover it from the available data set due to the large uncertainties on disc radius and width inherent in the marginally spatially resolved data, and the bias of smaller discs around more distant stars (which are also the more luminous) being omitted from our analysis. We see a trend in disc temperature as a function of stellar luminosity, consistent with previous findings from similar analyses.

Formation of Venus, Earth and Mars: Constrained by Isotopes

We discuss the current state of knowledge of terrestrial planet formation from the aspects of different planet formation models and isotopic data from 182Hf-182W, U-Pb, lithophile-siderophile elements, 48Ca/44Ca isotope samples from planetary building blocks, 36Ar/38Ar, 20Ne/22Ne, 36Ar/22Ne isotope ratios in Venus' and Earth's atmospheres, the expected solar 3He abundance in Earth's deep mantle and Earth's D/H sea water ratios that shed light on the accretion time of the early protoplanets. Accretion scenarios that can explain the different isotope ratios, including a Moon-forming event after ca. 50 Myr, support the theory that the bulk of Earth's mass (>80%) most likely accreted within 10-30 Myr. From a combined analysis of the before mentioned isotopes, one finds that proto-Earth accreted 0.5-0.6 MEarth within the first ~4-5 Myr, the approximate lifetime of the protoplanetary disk. For Venus, the available atmospheric noble gas data are too uncertain for constraining the planet's accretion scenario accurately. However, from the available Ar and Ne isotope measurements, one finds that proto-Venus could have grown to 0.85-1.0 MVenus before the disk dissipated. Classical terrestrial planet formation models have struggled to grow large planetary embryos quickly from the tiniest materials within the typical lifetime of protoplanetary disks. Pebble accretion could solve this long-standing time scale controversy. Pebble accretion and streaming instabilities produce large planetesimals that grow into Mars-sized and larger planetary embryos during this early accretion phase. The later stage of accretion can be explained well with the Grand-Tack, annulus or depleted disk models. The relative roles of pebble accretion and planetesimal accretion/giant impacts are poorly understood and should be investigated with N-body simulations that include pebbles and multiple protoplanets.

Evidence for post-nebula volatilisation in an exo-planetary body

The loss and gain of volatile elements during planet formation is key for setting their subsequent climate, geodynamics, and habitability. Two broad regimes of volatile element transport in and out of planetary building blocks have been identified: that occurring when the nebula is still present, and that occurring after it has dissipated. Evidence for volatile element loss in planetary bodies after the dissipation of the solar nebula is found in the high Mn to Na abundance ratio of Mars, the Moon, and many of the solar system's minor bodies. This volatile loss is expected to occur when the bodies are heated by planetary collisions and short-lived radionuclides, and enter a global magma ocean stage early in their history. The bulk composition of exo-planetary bodies can be determined by observing white dwarfs which have accreted planetary material. The abundances of Na, Mn, and Mg have been measured for the accreting material in four polluted white dwarf systems. Whilst the Mn/Na abundances of three white dwarf systems are consistent with the fractionations expected during nebula condensation, the high Mn/Na abundance ratio of GD362 means that it is not (>3σ). We find that heating of the planetary system orbiting GD362 during the star's giant branch evolution is insufficient to produce such a high Mn/Na. We, therefore, propose that volatile loss occurred in a manner analogous to that of the solar system bodies, either due to impacts shortly after their formation or from heating by short-lived radionuclides. We present potential evidence for a magma ocean stage on the exo-planetary body which currently pollutes the atmosphere of GD362.

Measuring the atomic composition of planetary building blocks

Context. Volatile molecules are critical to terrestrial planetary habitability, yet they are difficult to observe directly where planets form at the midplanes of protoplanetary disks. It is unclear whether the inner ∼1 AU of disks are volatile-poor or if this region is resupplied with ice-rich dust from colder disk regions. Dust traps at radial pressure maxima bounding disk gaps can cut off the inner disk from these types of volatile reservoirs. However, the trap retention efficiency and atomic composition of trapped dust have not been measured. Aims. We present a new technique to measure the absolute atomic abundances in the gas accreting onto T Tauri stars and infer the bulk atomic composition and distribution of midplane solids that have been retained in the disk around the young star TW Hya. Methods. We identify near-infrared atomic line emission from gas-phase material inside the dust sublimation rim of TW Hya. Gaussian decomposition of the strongest H Paschen lines isolates the inner disk hydrogen emission. We measure several key elemental abundances, relative to hydrogen, using a chemical photoionization model and infer dust retention in the disk. With a 1D transport model, we determine approximate radial locations and retention efficiencies of dust traps for different elements. Results. Volatile and refractory elements are depleted from TW Hya’s hot gas by factors of ∼102 and up to 105, respectively. The abundances of the trapped solids are consistent with a combination of primitive Solar System bodies. Dust traps beyond the CO and N2 snowline cumulatively sequester 96% of the total dust flux, while the trap at 2 AU, near the H2O snowline, retains 3%. The high depletions of Si, Mg, and Ca are explained by a third trap at 0.3 AU with >95% dust retention. Conclusion. TW Hya sports a significant volatile reservoir rich in C- and N-ices in its outer submillimeter ring structure. However, unless the inner disk was enhanced in C by earlier radial transport, typical C destruction mechanisms and the lack of a C resupply should leave the terrestrial planet-forming region of TW Hya “dry” and carbon-poor. Any planets that form within the silicate dust trap at 0.3 AU could resemble Earth in terms of the degree of their volatile depletion.

Dust condensation in evolving discs and the composition of planetary building blocks

ABSTRACT Partial condensation of dust from the Solar nebula is likely responsible for the diverse chemical compositions of chondrites and rocky planets/planetesimals in the inner Solar system. We present a forward physical–chemical model of a protoplanetary disc to predict the chemical compositions of planetary building blocks that may form from such a disc. Our model includes the physical evolution of the disc and the condensation, partial advection, and decoupling of the dust within it. The chemical composition of the condensate changes with time and radius. We compare the results of two dust condensation models: one where an element condenses when the mid-plane temperature in the disc is lower than the 50 per cent condensation temperature ($\rm T_{50}$) of that element and the other where the condensation of the dust is calculated by a Gibbs free energy minimization technique assuming chemical equilibrium at local disc temperature and pressure. The results of two models are generally consistent with some systematic differences of ∼10 per cent depending upon the radial distance and an element’s condensation temperature. Both models predict compositions similar to CM, CO, and CV chondrites provided that the decoupling time-scale of the dust is of the order of the evolution time-scale of the disc or longer. If the decoupling time-scale is too short, the composition deviates significantly from the measured values. These models may contribute to our understanding of the chemical compositions of chondrites, and ultimately the terrestrial planets in the Solar system, and may constrain the potential chemical compositions of rocky exoplanets.