Highly siderophile element evidence for early solar system processes in components from ordinary chondrites

Separated magnetic and nonmagnetic components from the ordinary chondrites Dhajala (H3.8) and Ochansk (H4) were analyzed for their Re-Os isotopic compositions, as well as for the abundances of the highly siderophile elements (HSE) Re, Os, Ir, Ru, Pt and Pd. The Re-Os isotopic systematics of these components are used to constrain the timing of HSE fractionations, and assess the level of open-system behavior of these elements in each of the different components. The high precision, isotope dilution mass spectrometric analyses of the HSE are used to constrain the origins of, and possible relations between some of the diverse components present in these chondrites. The relative and absolute abundances of the HSE differ considerably among the components. Metal fractions have Re/Os that are factors of ∼2 (Dhajala) to ∼3 (Ochansk) higher than those of their nonmagnetic fractions. The isotopic data for both meteorites are consistent with the largest Re-Os fractionations occurring between metal and nonmagnetic components early in solar system history, although minor to moderate late stage, open-system behavior, and limited variations in Re/Os preclude a precise determination of the age for that fractionation. Open-system behavior is generally absent to minor in the metal fractions, and highly variable in nonmagnetic fractions. Re/Os ratios of nonmagnetic fractions deviate as much as 40% from a primordial isochron. Although some deviations are large for isochron applications, nearly all are negligible with respect to consideration of fractionation processes controlling the HSE.Metal from both meteorites contains about 90% of the total budget of HSE. Metal in Ochansk has ∼2 to 10 times the abundances of the bulk meteorite, while metal from the matrix of Dhajala has ∼2 to 4 times the abundances of the bulk. Fine metal in both meteorites has higher abundances than coarse metal, as has been previously observed. Nonmagnetic components, consisting of chondrules and matrix from which metal was removed in the laboratory, have highly fractionated HSE, characterized by much lower Re/Os than the bulk meteorites, as well as large relative depletions in Pd. The abundances of Re, Os, Ir, Ru and Pt in the nonmagnetic fractions are 14-120 ng/g, much higher than would be expected if they had equilibrated with the metal phases present (150-16,000 ng/g). Collectively, the data are consistent with the HSE budget in ordinary chondrites being dominated by two HSE-bearing carrier phases with distinct compositions. These phases formed separately, and never subsequently equilibrated. Metal components incorporated a HSE carrier that formed at high through moderate temperatures and relatively high pressures, such that the relatively volatile Pd behaved coherently with the more refractory HSE. Nonmagnetic fractions from both chondrules and matrix have HSE compositions that likely require at least two processes that fractionated the HSE. Depletions in Pd are consistent with the presence of HSE carriers that formed as either highly refractory condensates, or residues of high degrees of metal melting. Depletions in Re may implicate a period of relatively high f_O2 during which a volatile form of Re was separated from the other HSE.     

Surface properties of the Orgueil meteorite: implications for the early history of solar system volatiles

Dehydration of Orgueil by stepwise calcination produced more than a tenfold change in its Kr B.E.T. surface area, which increased to 120 m²/g, then fell to 40 m²/g. This phenomenon characterizes structures of the montmorillonite type, but not other plausible constituents of Orgueil. It results from vacating of interlayer sites by H₂O molecules which are replaced by Kr until finally the sheets collapse, excluding Kr. Differential calorimetric scans of Orgueil also gave a better match for montmorillonite than for other minerals. However, a simple identification as montmorillonite conflicts with chemical analyses of Orgueil phyllosilicates.Exchangeability of H₂O in Orgueil was shown by water regain from lab air between calcination cycles and similarily of the cycles. Room temperature dehydration revealed up to 6 per cent free surface adsorbed water. High D/H ratios in CI's may result from D enrichment in OH^? groups during equilibration of dispersed phyllosilicate dust with nebula gas at temperatures ?0°C. Adsorption on the very large free and interlayer surface areas of this dust was the major mechanism by which volatiles still uncondensed at the time of gas-dust separation (including planetary primordial Ar, Kr and Xe) were incorporated into solid solar system material.     

An ordinary chondrite impactor for the Popigai crater, Siberia

With a diameter of ∼100 km, Popigai in Northern Siberia is the largest crater known in the Cenozoic. The concentrations in platinum group elements (PGE) were analyzed in twenty samples of homogeneous impact melt collected in the northwestern flank of the crater to identify the composition of the projectile. The method selected was preconcentration by NiS fire assay followed by inductively coupled plasma-mass spectrometry (ICP-MS). This technique measures all the PGE (except Os) and by using aliquots >10g, the results are highly reproducible. The major and trace element composition of the impact melt resembles that of gneissic lithologies of the Anabar shield, which are representative of the target rock. The PGE are enriched in the melt by factors of 3 to 14 compared to the main target lithology, but the meteoritic contamination is only around 0.2 wt.%. Using plots of elemental ratios such as Ru/Rh vs. Pt/Pd or Ru/Rh vs. Pd/Ir, the Popigai impactor is clearly identified as an ordinary chondrite and most likely l-chondrite. This study indicates that PGE elemental ratios allow discrimination of the type of impactor, even in the case of low meteoritic contamination. This study confirms that a significant fraction of the crater-forming projectiles presently documented could have an ordinary chondrite composition. Their probable source, the S-type asteroids, appears to form the majority of the bodies in the main asteroid belt and among Near Earth Objects (NEOs). The ordinary chondrite origin of the Popigai projectile supports an asteroidal origin for the late Eocene impacts as a plausible alternative to the comet shower scenario proposed by Farley et al. (1998).     

普通球粒陨石 Semarkona中球粒的 Pb-Pb法年龄

陨石年代学研究中常用定年工具包括短半衰期和长半衰期放射性同位素体系,其中前者可以给出陨石形成的相对年龄,而后者则可以给出绝对形成年龄。在长半衰期体系中,PbP-b法是目前能获得高精度可靠年龄的最有效方法。普通球粒陨石Sem arkona是最不平衡的LL3.0型陨石,受后期热变质的影响很小,因此其年龄研究对反演陨石起源有重要意义。在本文中,对Sem arkona中球粒用不同的化学浸洗流程,并测定浸洗溶液和残渣中UT-hP-b同位素组成,其中浸洗后的残渣均给出相对较高的206Pb/204Pb比值,表明其中含有较多的放射成因Pb同位素组成,这些残渣构成PbP-b等时线,给出年龄为(4566.9±5.8)M a,M SW D=26,与207Pb/206Pb模式年龄在误差范围内一致。尽管Sem arkona陨石可能经历了后期蚀变的影响,但前人对陨石变质温度的研究结果表明,热变质温度并未足以使球粒中Pb同位素体系重置,因此获得的年龄代表Sem arkona陨石球粒的形成年龄。     

Petrography and classification of NWA 7402: A new sulfide-rich unequilibrated ordinary chondrite

We classify a new chondritic find Northwest Africa (NWA) 7402. This meteorite is highly unequilibrated, and is therefore potentially significant for the study of primitive Solar System materials. Mineralogy, mineral chemistry, and modal abundances of minerals indicate that NWA 7402 is most likely an L chondrite. However, the specimen contains a higher abundance of sulfide than commonly seen in ordinary chondrites. The structural order of organic matter in the matrix and the chromium content of Fe-rich olivine grains indicate a petrologic type of 3.1. NWA 7402 largely escaped thermal metamorphism, and secondary phases formed by aqueous alteration are rare to absent. Minor planar fractures and undulatory extinction of olivine grains suggest that NWA 7402 experienced shock up to stage 2 or 3. Terrestrial weathering is heterogeneous in the specimen; much of the stone's exterior shows substantial Fe oxidation (weathering grade 2), while some parts of the interior remain relatively fresh (weathering grade 1). NWA 7402 has some unusual features that should be investigated further. The sulfide abundance is higher than reported sulfide contents for other L chondrites, and the chromium content of the olivines does not fall on the trend established for unequilibrated ordinary chondrites by Grossman and Brearley (2005).     

荷叶塘陨石:一个L3型普通球粒陨石的岩石学和地球化学特征

荷叶塘为一块我国降落的原始3型普通球粒陨石,因此具有重要研究意义。本文对荷叶塘陨石光薄片及粉末样品的岩石学、矿物学和全岩组成地球化学特征进行研究,为这块陨石的深入研究提供重要基础数据。研究表明荷叶塘陨石具L3型陨石岩石学特征,具典型的球粒陨石结构,球粒清晰,球粒结构类型多,基质重结晶程度低,组成模式为:球粒80vol%,金属和硫化物含量为5vol%,基质15vol%。矿物化学成分表明,该陨石球粒以Ⅰ型(贫铁型)球粒为主,橄榄石Fa0.41-34.1(PMD=51),低钙辉石Fs1.82-27.2(PMD=88),Wo0.18-3.13(PMD=103),铁纹石中Co含量平均0.62%(PMD=20),矿物成份不均一程度高,橄榄石矿物结晶颗粒内部化学成分变化大,呈正环带分布,与岩浆型结晶顺序一致,球粒与基质及间隙物成分明显不同,表现为不同物质来源。化学成分全岩分析结果显示,荷叶塘陨石亲石、亲铁元素含量均为L型陨石特征。依据以上岩石矿物学和化学组成特征,依照陨石亚分类参数,将其类型划分为L3.4型普通球粒陨石。冲击变质程度S2,风化程度W1。研究结果表明荷叶塘陨石为一块受后期水、热蚀变和风化影响较少的原始类型陨石。组成矿物成分极不均一,在矿物晶体内部,球粒内部及球粒与基质间均有明显变化。     

Iodine-xenon analysis of Chainpur (LL3.4) chondrules

We present I-Xe analyses of ten chondrules from Chainpur LL3.4 by IR laser-stepped heating. Five chondrules provided isochrons of varying quality, giving a range of ages from 0.5 Ma before Shallowater to 17.8 after Shallowater. This confirms the extended range of Chainpur chondrule ages determined by previous data. We discuss evidence for fluid alteration, shock, and thermal events in explaining the chondrule ages and suggest that chondrule remelting events, presumably from bombardment of the parent body surface, are responsible for resetting the I-Xe chronometer. Previous data show a negative correlation between ¹³²Xe/¹²⁹Xe of the trapped Xe component and ¹²⁷I/¹²⁹I of an initial iodine component. This behaviour that requires the presence of a component with trapped ¹²⁹Xe/¹³²Xe lower than the planetary value has been cited as evidence for closed system evolution of the I-Xe system. We find no evidence of an unambiguous trapped component lower than planetary and no evidence of a negative correlation in our data. Therefore we suggest that open system behaviour more suitably explains the I-Xe systematics of Chainpur chondrules.     

Short-lived nuclides in the early solar system

Isotopic records in meteorites provide evidence for the presence of several short-lived nuclides in the early solar system with half-lives varying from 10⁵ to ∼8x10⁷ years. Most of the nuclides with longer half-life (> 10⁷ years) are considered to be products of stellar nucleosynthesis taking place over long time scales in our galaxy. However, for the relatively shorter-lived nuclides, two possibilities exist; they could be products of energetic particle interactions taking place in a presolar or early solar environment, or, they could have been produced in a stellar source and injected into the protosolar molecular cloud just prior to its collapse. The presently available data appear to support the latter case and put a stringent constraint of less than a million years for the time scale for the collapse of the protosolar molecular cloud to form the Sun and some of the first solar system solids. This short time scale also suggests the possibility of a triggered origin for the solar system with the very process of injection of the short-lived nuclides acting as the trigger for the collapse of the protosolar molecular cloud. Fossil records of the short-lived nuclides in meteorites also provide very useful chronological information on the early solar system processes like the time scale for nebular processing, the time scales for differentiation and for metal/silicate fractionation within planetesimals. The currently available data suggest a time scale of a few million years for nebular processing and a relatively short time scale of about ten million years within which differentiation, melting and recrystallization in some of the planetesimals took place.     

Nitrogen isotopes in the recent solar wind from the analysis of Genesis targets: Evidence for large scale isotope heterogeneity in the early solar system

We have analyzed nitrogen, neon and argon abundances and isotopic ratios in target material exposed in space for 27 months to solar wind (SW) irradiation during the Genesis mission. SW ions were extracted by sequential UV (193 nm) laser ablation of gold-plated material, purified separately in a dedicated line, and analyzed by gas source static mass spectrometry. We analyzed gold-covered stainless steel pieces from the Concentrator, a device that concentrated SW ions by a factor of up to 50. Despite extensive terrestrial N contamination, we could identify a non-terrestrial, ¹⁵N-depleted nitrogen end-member that points to a 40% depletion of ¹⁵N in solar-wind N relative to inner planets and meteorites, and define a composition for the present-day Sun (¹⁵N/¹⁴N = [2.26 ± 0.67] × 10⁻³, 2σ), which is indistinguishable from that of Jupiter’s atmosphere. These results indicate that the isotopic composition of nitrogen in the outer convective zone of the Sun has not changed through time, and is representative of the protosolar nebula. Large ¹⁵N enrichments due to e.g., irradiation, low temperature isotopic exchange, or contributions from ¹⁵N-rich presolar components, are therefore required to account for inner planet values.     

Chronology of meteorites and the early solar system

Understanding the chronology of the chondritic and differentiated meteorites can potentially important constraints on the accretion and origin of the solar system planets, life-time of our protoplanetary disk and circumstellar disks around solar mass stars, and astrophysical setting of the solar system formation. The special issue of Geochimica et Cosmochimica Acta consists of invited and contributed papers presented at the Workshop on The Chronology of Meteorites and the Early Solar System, Kauai, 2007 and is honoring the outstanding contributions of C.J. Allégre, G.W. Lugmair, L.E. Nyquist, D.A. Papanastassiou, and G.J. Wasserburg to our understanding of the chronology of the early Solar System.     

Isotopic analysis of early solar system objects by an ion microprobe: Parametric studies and initial results

Magnesium, potassium and calcium isotope compositions in terrestrial samples and refractory phases from primitive meteorites are determined using an ion microprobe. A thorough investigation of the different instrument parameters is carried out to ensure that conditions necessary for high mass resolution and high precision isotopic studies are adequately satisfied. The instrument can be tuned to achieve mass resolution (M/ΔM) of up to 10,000 (M≤60); it has a very good dynamic stability (ΔB/B≤10 ppm over durations of ≤40 minutes) and the counting system has an effective dead-time of ≤25 nsec and a dynamic background of ≤0·01 c/s. Reproducibility and precision of isotopic measurements are checked by analyzing magnesium and titanium isotopic compositions in terrestrial standards and isotopically doped silicate glasses. A precision of 2‰ (2σ _m ) was achieved during magnesium isotopic analysis in samples with low Mg content (200 ppm). Results from studies of magnesium and potassium isotopic compositions in several Ca−Al-rich refractory inclusions (CAIs) from the primitive meteorites Efremovka and Grosnaja, representing some of the early solar system objects, are presented. The well-behaved Mg−Al isotopic systematics confirm the pristine nature of the Efremovka CAIs inferred earlier from petrographic and trace element studies. The Grosnaja CAIs that have experienced secondary alterations show disturbed magnesium isotopic systematics. Observation of excess²⁶Mg in several of the analyzed CAIs confirms the presence of the now extinct²⁶Al (t _1/2=7×10⁵ years) in the solar nebula at the time of CAI formation. Our data also suggest a relatively uniform distribution of²⁶Al in the solar nebula. Several Efremovka CAIs with excess²⁶Mg also have excess⁴¹K resulting from the decay of⁴¹Ca (t _1/2≃10⁵ years). This observation constrains the time interval between cessation of nucleosynthetic input to the solar nebula and the formation of some of the first solar system solids (CAIs) to less than a million years.     

Extreme Cr-rich nano-oxides in the CI chondrite Orgueil - Implication for a late supernova injection into the solar system

Systematic variations in ⁵⁴Cr/⁵²Cr ratios between meteorite classes ( [Trinquier et al., 2007] and [Qin et al., 2010a]) point to large scale spatial and/or temporal isotopic heterogeneity in the solar protoplanetary disk. Two explanations for these variations have been proposed, with important implications for the formation of the Solar System: heterogeneous seeding of the disk with dust from a supernova, or energetic-particle irradiation of dust in the disk. The key to differentiating between them is identification of the carrier(s) of the ⁵⁴Cr anomalies. Here we report the results of our recent NanoSIMS imaging search for the ⁵⁴Cr-rich carrier in the acid-resistant residue of the CI chondrite Orgueil. A total of 10 regions with extreme ⁵⁴Cr-excesses (δ⁵⁴Cr values up to 1500‰) were found. Comparison between SEM, Auger and NanoSIMS analyses showed that these ⁵⁴Cr-rich regions are associated with one or more sub-micron (typically less than 200 nm) Cr oxide grains, most likely spinels. Because the size of the NanoSIMS primary O⁻ ion beam is larger than the typical grain size on the sample mount, the measured anomalies are lower limits, and we estimate that the actual ⁵⁴Cr enrichments in three grains are at least 11 times Solar and in one of these may be as high as 50 times Solar. Such compositions strongly favor a Type II supernova origin. The variability in bulk ⁵⁴Cr/⁵²Cr between meteorite classes argues for a heterogeneous distribution of the ⁵⁴Cr carrier in the solar protoplanetary disk following a late supernova injection event. Such a scenario is also supported by the O-isotopic distribution and variable abundances in different planetary materials of other presolar oxide and silicate grains from supernovae.     

Lead isotopes in tap water: implications for Pb sources within a municipal water supply system

Residential tap waters were investigated to examine the feasibility of using isotopic ratios to identify dominant sources of water Pb in the Columbus (Ohio, USA) municipal supply system. Overall, both the concentrations, which are generally low (0.1–28 μg/L), and isotopic compositions of tap water Pb show wide variations. This contrasts with the situation for a limited number of available service lines, which exhibit only a limited Pb-isotope variation but contain Pb of two very different types with one significantly more radiogenic than the other. Most tap water samples in contact with Pb service lines have Pb-isotope ratios that are different from the pipe Pb. Furthermore, the Pb isotope compositions of sequentially drawn samples in the same residence generally are similar, but those from separate residences are different, implying dominant Pb sources from domestic plumbing. A separate pilot study at two residences without Pb service lines shows isotopic similarity between water and solders in each house, further suggesting that the major Pb sources are domestic in these cases and dominated by Pb from solder joints. Although complicated by the broad range of overall Pb-isotope variations observed and limited by sample availability, the results suggest that Pb isotopes can be used effectively to constrain the sources of Pb in tap waters, especially for individual houses where multiple source candidates can be identified.     

Metallic minerals,thermal histories and parent bodies of some xenolithic,ordinary chondrite meteorites

We have studied metal grains in the hosts and lithic fragments of widely differing petrologic types in four xenolithic chondrftes, using reflected-light microscopy and electron-probe analysis. In Weston and Fayetteville, which both contain solar-flare tracks and solar-wind gases, kamacite, taenite and tetrataenite (ordered FeNi) and troilite show a variety of textures. On a Wood plot of central Ni content vs dimension, taenite analyses scatter as if metal grains cooled at rates of 10–1000 and 1–100 K/Myr respectively through 700 K, although metal in an H6 clast in Fayetteville plots coherently with a cooling rate of 50 K/Myr. We propose that metal grains cooled at these rates in chondritic clasts at different locations before host and clasts were compacted, and were not subsequently heated above 650 K. We predict a similar history for all gas-rich ordinary chondrites.By contrast, metallic minerals throughout Bhola and Mezö-Madaras show more uniform textures and plot coherently giving cooling rates in the range 750 to ~600 K of 0.1 and 1 K/Myr, respectively. We conclude that host and xenoliths in both chondrites were slowly cooled after compaction. Thus clasts in these chondrites experienced peak metamorphic temperatures and slow cooling through 700 K in different environments.According to the conventional onion-shell model for H, L or LL chondrite parent bodies, material of petrologic types 3–5 was arranged in successive shells around a type 6 core prior to catastrophic collisions which mixed all types intimately. But if peak metamorphic temperatures were reached during, not after accretion, as seems plausible, maximum metamorphism may have occurred in planetesimals <10 km in radius. Cooling through 700 K may then have occurred in larger bodies that accreted from these planetesimals. Iron meteorites, mesosiderites and some achondrites may also have experienced melting in planetesimals and slow cooling in larger bodies.     

In search of live Cm in the early solar system

The r-process only nuclide ²⁴⁷Cm decays to ²³⁵U with a characteristic half-life of ∼16 million years. ²⁴⁷Cm is presently extinct, but offers considerable potential as a short-lived r-process chronometer, providing constraints on the time interval between the last r-process nucleo-synthetic event and the formation of the solar system. The existence of “live” ²⁴⁷Cm in the early solar system should be manifested today as variations in ²³⁵U/²³⁸U, provided Cm was chemically fractionated from U when solids formed in the early solar system. Using multiple-collector ICPMS and a high-purity mixed ²³³U-²³⁶U spike to monitor instrumental mass fractionation, we are able to resolve variations in ²³⁵U/²³⁸U at the 1-2 epsilon level (2σ_M; 1 epsilon = 1 part in 10,000) on sample sizes consisting of 20 ng of uranium. Data can be acquired on smaller (<10 ng) samples with ±2-3 epsilon 2σ uncertainties. Uranium isotopic measurements and U, Nd and Sm concentrations were acquired on bulk samples of a suite of carbonaceous chondrites, unequilibrated and equilibrated ordinary chondrites and eucrites, for which conflicting results had previously been obtained. Our results show no well-resolved excursions in ²³⁵U/²³⁸U away from the terrestrial value at the ∼2 epsilon level, and constrain the amount of ²⁴⁷Cm-produced excess ²³⁵U atoms to less than ∼1 × 10⁸ atoms per gram of chondritic meteorite, with respect to terrestrial ²³⁵U/²³⁸U. Large (permil- level) anomalies in ²³⁵U/²³⁸U could, however, be artificially generated in the ordinary chondrites during laboratory processing. Therefore, U may be more susceptible to isotopic fractionation during chemical processing than previously recognized, and may reconcile some of the highly conflicting ε²³⁵U results reported by previous workers for chondritic meteorites. Our results indicate that a timescale of ∼1-2 × 10⁸ years between the last actinide producing r-process event and the formation of the solar system may not be unreasonable based on the ²⁴⁷Cm-²³⁵U system. However, this conclusion is far from robust at this stage because the only bulk meteorites analysed that display strong Nd/U fractionation are highly metamorphosed chondrites that may have experienced a protracted history of redistribution and re-equilibration. The search for “live” ²⁴⁷Cm in the early solar system can now be extended to early-formed condensates and mineral phases displaying strong Cm-U fractionations.     

53Mn-53Cr evolution of the early solar system

The model of Cr isotopic evolution presented here, relies on the relative volatility properties of the two elements: Mn-Cr in planetary formation processes. The Mn/Cr ratio of the respective parent bodies correlate in most cases with the K/U ratio. With the exception of Allende inclusions, the ⁵³Mn/⁵⁵Mn and ⁵³Cr/⁵²Cr isotopic ratios were homogeneous in the solar nebula. The Cr isotopic evolution of the bulk solar system corresponds to the C1 carbonaceous chondrites. In this figure the Earth is isolated within a few million years of the C1 formation, from the solar nebula before complete decay of ⁵³Mn. It has a Cr isotopic composition which is depleted in ⁵³Cr with respect to the solar system as a whole. The parent bodies of the different meteorite classes display various behaviour with no case of Mn enrichment relative to Cr when compared to C1. The ⁵³Mn-⁵³Cr isotopic system is a precise tool for the exploration of the early solar sytem history, bringing constraints both on time and processes in this phase of the evolution where the face of the planetary system was changing rapidly. The chronology deduced from Mn-Cr systematics, is generally in good agreement with other chronometers.     

Presolar grains from meteorites: Remnants from the early times of the solar system

This review provides an introduction to presolar grains - preserved stardust from the interstellar molecular cloud from which our solar system formed - found in primitive meteorites. We describe the search for the presolar components, the currently known presolar mineral populations, and the chemical and isotopic characteristics of the grains and dust-forming stars to identify the grains’ most probable stellar sources.     

Short-lived radioactive nuclides in meteorites and early solar system processes

Now extinct, short-lived radioactive nuclides, such as ⁷Be (T_1/2 = 53 days), ¹⁰Be (T_1/2 = 1.5 Ma), ²⁶Al (T_1/2 = 0.74 Ma), ³⁶Cl (T_1/2 = 0.3 Ma), ⁴¹Ca (T_1/2 = 0.1 Ma), ⁵³Mn (T_1/2 = 3.7 Ma) and ⁶⁰Fe (T_1/2 = 1.5 Ma), were present in the protosolar nebula when the various components of meteorites formed. The presence of these radioactive isotopes requires a ‘last-minute’ origin, either nucleosynthesis in a massive star dying close in space and time to the nascent solar system or production by local irradiation of part of the protosolar disk by high-energy solar cosmic rays. In this review, we list: (i) the different observations indicating the existence of multiple origins for short-lived radioactive nuclides, namely ⁷Be, ¹⁰Be and ³⁶Cl for irradiation scenario and ⁶⁰Fe for injection scenario; (ii) the constraints that exist on their distribution (homogeneous or heterogeneous) in the accretion disk; (iii) the constraints they brought on the timescales of nebular processes (from Ca–Al-rich inclusions to chondrules) and of the accretion and differentiation of planetesimals.     

Stellar sources of the short-lived radionuclides in the early solar system

We discuss the possible stellar sources of short-lived radionuclides (SLRs) known to have been present in the early solar system (²⁶Al, ³⁶Cl, ⁴¹Ca, ⁵³Mn, ⁶⁰Fe, ¹⁰⁷Pd, ¹²⁹I, ¹⁸²Hf, ²⁴⁴Pu). SLRs produced primarily by irradiation (⁷Be, ¹⁰Be) are not discussed in this paper. We evaluate the role of the galactic background in explaining the inventory of SLRs in the early solar system. We review the nucleosynthetic processes that produce the different SLRs and place the processes in the context of stellar evolution of stars from 1 to 120 M_⊙. The ejection of newly synthesized SLRs from these stars is also discussed. We then examine the extent to which each stellar source can, by itself, explain the relative abundances of the different SLRs in the early solar system, and the probability that each source would have been in the right place at the right time to provide the SLRs. We conclude that intermediate-mass AGB stars and massive stars in the range from ∼20 to ∼60 M_⊙ are the most plausible sources. Low-mass AGB stars fail to produce enough ⁶⁰Fe. Core-collapse Type II supernovae from stars with initial masses of <20 M_⊙ produce too much ⁶⁰Fe and ⁵³Mn. Sources such as novae, Type Ia supernovae, and core-collapse supernovae of O-Ne-Mg white dwarfs do not appear to provide the SLRs in the correct proportions. However, intermediate-mass AGB stars cannot provide ⁵³Mn or the r-process elements, so if an AGB star provided the ⁴¹Ca, ³⁶Cl, ²⁶Al, ⁶⁰Fe, and ¹⁰⁷Pd, and if a late stellar source is required for ⁵³Mn and the r-process elements, then two types of sources would be required. A separate discussion of the production of r-process elements highlights the difficulties in modeling their production. There appear to be two sources of r-process elements, one that produces the heavy r-process elements, including the actinides, and one that produces the elements from N to Ge and the elements ∼110 < A < ∼130. These can be assigned to SNII explosions of stars of ?11 M_⊙ and stars of 12-25 M_⊙, respectively. More-massive stars, which leave black holes as supernova remnants, apparently do not produce r-process elements.