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Initial analyses showed that asteroid Ryugu's composition is close to CI (Ivuna-like) carbonaceous chondrites (CCs) - the chemically most primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (for example, Ti, Cr) overlap with other CC groups, so the details of the link between Ryugu and the CI chondrites are not yet fully clear. Here we show that Ryugu and CI chondrites have the same zinc and copper isotopic composition. As the various chondrite groups have very distinct Zn and Cu isotopic signatures, our results point at a common genetic heritage between Ryugu and CI chondrites, ruling out any affinity with other CC groups. Since Ryugu's pristine samples match the solar elemental composition for many elements, their Zn and Cu isotopic compositions likely represent the best estimates of the solar composition. Earth's mass-independent Zn isotopic composition is intermediate between Ryugu/CC and non-carbonaceous chondrites (NCs), suggesting a contribution of Ryugu-like material to Earth's budgets of Zn and other moderately volatile elements.

Key events in the early history of the Moon include its formation by a giant impact, the solidification of the lunar magma ocean, and late accretion. The 182Hf-182W system (t1/2 ~9 Ma) constitutes a versatile tool to study each of these processes because they can all result in measurable 182W variations. Here we review the 182W record of lunar rocks and highlight key constraints on the early evolution of the Moon. Tungsten isotope studies on lunar samples demonstrate that there are no resolvable 182W variations within the Moon, implying that lunar magma ocean differentiation later than ~70 Ma after Solar System formation. Nevertheless, the Moon is characterized by a uniform ~25 parts-per-million 182W excess over the present-day bulk silicate Earth (BSE). One possibility is that this 182W difference is radiogenic in origin, in which case the Hf-W system can potentially be used to date the formation of the Moon. However, this interpretation is problematic for two reasons. First, mixing processes during the giant impact very likely modified the 182W composition of the Moon and led to distinct initial 182W compositions of the Moon and Earth. Second, the pre-late accretion 182W compositions of the Moon and BSE overlap within uncertainty, and hence there is no resolved radiogenic 182W difference between the BSE and the Moon. Consequently, the Hf-W system does not provide reliable constraints on the age of the Moon. Instead, the Hf–W systematics are fully consistent with 'young' ages of the Moon, well after the effective lifetime of 182Hf.

We provide critical new insights into the nature and origin of a widespread isotope effect for W: it is inconsistent with a nuclear field shift, induced during the chemical separation procedure, and also controlled by the amount of W processed.

Correction to: Nature Astronomy https://doi.org/10.1038/s41550-022-01846-1. Published online 12 December 2022.

Tellurium stable isotope compositions and abundances (δ128/126Te relative to SRM 3156) are reported for 43 ordinary, enstatite, and Rumuruti chondrites, which together with results from a companion study on carbonaceous chondrites are used to assess the origin of volatile element fractionations in chondrites. Whereas Te isotope variations among carbonaceous chondrites predominantly reflect mixing between isotopically light chondrules/chondrule precursors and CI-like matrix, Te isotope variations among non-carbonaceous chondrites mainly result from Te redistribution during parent body thermal metamorphism. The enstatite chondrites in particular display increasingly heavy Te isotopic compositions and decreasing Te concentrations with increasing degree of metamorphism, indicating migration of isotopically light Te from the strongly metamorphosed inner parts towards the cooler outer regions of the parent bodies. By contrast, ordinary and Rumuruti chondrites display less systematic Te isotope variations, implying more localized redistribution of Te during parent body thermal metamorphism. We also report Te stable isotope data for 19 terrestrial mantle-derived rocks. Peridotites with Al2O3 contents close to those inferred for the bulk silicate Earth (BSE) exhibit uniform δ128/126Te values, which we interpret to represent the Te isotopic composition of the BSE. This composition overlaps with the Te isotope composition of some volatile-rich carbonaceous chondrites (most notably CM chondrites), but also with that of enstatite chondrites. Comparison of the Te results to Se isotopes and Se/Te ratios shows that due to uncertainties in the composition of the BSE and the isotopic composition of bulk chondrite parent bodies, neither Te isotopes alone nor the combined Se-Te elemental and isotopic systematics can distinguish between a carbonaceous and enstatite chondrite-like late veneer, which is the presumed source of Se and Te in the BSE. Together, the results of this study illustrate that the relative abundances and mass-dependent isotope compositions of volatile elements like Se and Te are modified by physical and chemical processes occurring after planetary accretion, which severely complicates their use as genetic tracers. A corollary of this is that contrary to prior proposals the Se-Te systematics are not contradicting an inner solar system origin of the late veneer, as it has been inferred using nucleosynthetic isotope anomalies of other elements.

A coordinated study of the petrology, mineral chemistry, and bulk chemical and isotopic composition of the five ungrouped carbonaceous chondrites Coolidge, Loongana 001, Los Vientos (LoV) 051, Northwest Africa (NWA) 033, and NWA 13400 reveals that these meteorites have a similar set of properties that distinguishes them from the other carbonaceous chondrite groups and allows definition of the new Loongana (CL) group of carbonaceous chondrites. The basic characteristics of the investigated samples are: (1) Lithophile element ratios (e.g., Al/Mg, Si/Mg) are within the typical range of other carbonaceous chondrite groups. (2) Fe-Ni metal abundances are considerably higher than for CV, but similar to CR chondrites. (3) Chondrule size-frequency distributions are similar to CV, but dissimilar to CR chondrites. (4) The mean CAI abundance is ∼1.4 vol%, i.e., lower than in CV but much higher than in CR chondrites. (5) Very low amounts of matrix (17-21 vol%), the lowest among the main carbonaceous chondrite groups (CI, CM, CO, CV, CR, CK). (6) Olivine is nearly equilibrated, with mean fayalite (Fa) values between 12.5 mol% (Loongana 001) and 14.7 mol% (NWA 13400) as a metamorphic effect. (7) Lower Al2O3 and higher MgO and Cr2O3 concentrations in matrix, compared to matrix in CV, CK, and CR chondrites. (8) Volatile elements (Mn, Na, K, Rb, Cs, Zn, Se, Te, Pb, Tl) are considerably depleted compared to all other main carbonaceous chondrite groups, reflecting the low matrix abundance. (9) Bulk O isotope compositions plot along the CCAM line (Δ17O -3.96 to -5.47‰), partly overlapping with the CV and CK chondrite field but including samples that are more 16O-rich. (10) Unique positions of CL values in the є54Cr-є50Ti isotope plot, with є54Cr values similar to CV, CK, and CO, but є50Ti values similar to CR chondrites. All CL chondrites studied here are of petrologic type 3.9 to 4, indicating that they have been thermally metamorphosed on the parent body. The diagnostic features of CL chondrites detailed here provide a basis for identifying CL members of lower petrologic types. Such samples will be important for determining the pristine state of these meteorites and their components.

Primitive achondrites derive from the residual mantle of incompletely differentiated planetesimals, from which partial silicate and metallic melts were extracted. As such, primitive achondrites are uniquely useful to examine the early stages of planetesimal melting and differentiation. To better understand this early melting and melt segregation as well as the nature of the melts involved, we obtained mass-dependent Ru isotopic compositions of 17 primitive achondrites, including winonaites, acapulcoite-lodranites, ureilites, brachinites, and two ungrouped samples. Most primitive achondrites with subchondritic Ru concentrations are characterized by heavy Ru isotopic compositions relative to chondrites, likely reflecting the extraction of isotopically light partial metallic melts. While the segregation of early-formed partial Fe-Ni-S melts likely had no effect on the Ru isotope compositions, the subsequent extraction of S-free partial metallic melts at higher temperatures provides a viable mechanism for producing the observed Ru isotopic fractionation and fractionated highly siderophile element ratios among primitive achondrites. Together, these observations indicate that differentiation of primitive achondrite parent bodies involved the segregation of distinct partial metallic melts over a range of temperatures, and that these melts ultimately formed a partial core with fractionated and light Ru isotopic composition. This contrasts with the unfractionated Ru isotope signatures previously estimated for bulk iron meteorite cores, which therefore indicates quantitative metal segregation during core formation in the iron meteorite parent bodies. The less efficient metal segregation in primitive achondrite parent bodies most likely reflects lower initial amounts of heat-producing 26Al due to later accretion or impact disruption of the parent bodies during differentiation.

Timing Solar System formation The oldest solids that formed in the Solar System are calcium-aluminium–rich inclusions (CAIs), small metallic droplets that were later incorporated into meteorites. The ages of CAIs are conventionally taken as the age of the Solar System, but which exact moment in star formation they correspond to has been unclear. Brennecka et al. measured molybdenum isotope ratios in CAIs and found a wide range of origins in both the inner and outer Solar System. They propose that CAIs formed from heterogeneous material accreting from the presolar nebula and that the ages of CAIs coincide with the Sun's transition from a protostar to a pre–main sequence star. Science , this issue p. 837

A large, igneous-textured, and 2 cm-sized spherical object from the L5/6 chondrite NWA 8192 was investigated for its chemical composition, petrography, O isotopic composition, and Hf-W chronology. The petrography and chemical data indicate that this object closely resembles commonly found chondrules in ordinary chondrites and is therefore classified as a “macrochondrule.* As a result of metal loss during its formation, the macrochondrule exhibits elevated Hf/W, which makes it possible to date this object using the short-lived 182Hf-182W system. The Hf-W data provide a two-stage model age for metal–silicate fractionation of 1.4 ± 0.6 Ma after Ca-Al-rich inclusion (CAI) formation, indicating that the macrochondrule formed coevally to normal-sized chondrules from ordinary chondrites. By contrast, Hf-W data for metal from the host chondrite yield a younger model age of ~11 Ma after CAIs. This younger age agrees with Hf-W ages of other type 5–6 ordinary chondrites, and corresponds to the time of cooling below the Hf-W closure temperature during thermal metamorphism on the parent body. The Hf-W model age difference between the macrochondrule and the host metal demonstrates that the Hf-W systematics of the bulk macrochondrule were not disturbed during thermal metamorphism, and therefore, that the formation age of such objects can still be determined even in strongly metamorphosed samples. Collectively, this study illustrates that chondrule formation was not limited to mm-size objects, implying that the rarity of macrochondrules reflects either that this process was very inefficient, that subsequent nebular size-sorting decimated large chondrules, or that large precursors were rare.

To better constrain the crystallization and cooling history of the IIIAB iron meteorite parent body, we report new 107Pd-107Ag data for metal and troilite samples from the IIIAB iron Cape York, and combine these data with a numerical model for the diffusive exchange of 107Ag between metal and troilite. We find that the Pd-Ag closure temperature for iron meteorites varies between 500 and 700 °C, and for most irons typically is between 550 and 650 °C. The closure temperature not only depends on cooling rate, grain size, and bulk Ni content, but also on the abundance and distribution of troilite nodules. Specifically, metal in direct contact to troilite has a lower closure temperature than more distant metal. Consistent with this, our new Pd-Ag data show that metals adjacent to troilites have lower Ag contents and plot on shallower Pd-Ag isochrons than more distant metals. These disparate Pd-Ag systematics in metal as a function of distance to troilite provide a new means to determine cooling rates for iron meteorites. Using this approach, we obtained a cooling rate of 67–202 °C/Ma for Cape York, which is in good agreement with metallographic cooling rates for IIIAB irons. This cooling rate combined with the precise Pd-Ag age of Cape York of 5.0 ± 0.4 Ma after solar system formation reveals that the IIIAB core completely solidified at 2.6 ± 1.3 Ma after solar system formation. This rapid crystallization was most likely facilitated by collisional disruption of the IIIAB parent body, which removed most of the insulating mantle and exposed its core.

Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measured the mineralogy and bulk chemical and isotopic compositions of Ryugu samples. The samples are mainly composed of materials similar to those of carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37° ± 10°C, about 5.2 − 0.7 + 0.8 million (statistical) or 5.2 − 2.1 + 1.6 million (systematic) years after the formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles that of the Sun’s photosphere than other natural samples do.

Description, An integrated assessment of isotopic variations among meteorites reveals the process by which Earth and Mars are formed., Two fundamentally different processes of rocky planet formation exist, but it is unclear which one built the terrestrial planets of the solar system. They formed either by collisions among planetary embryos from the inner solar system or by accreting sunward-drifting millimeter-sized “pebbles” from the outer solar system. We show that the isotopic compositions of Earth and Mars are governed by two-component mixing among inner solar system materials, including material from the innermost disk unsampled by meteorites, whereas the contribution of outer solar system material is limited to a few percent by mass. This refutes a pebble accretion origin of the terrestrial planets but is consistent with collisional growth from inner solar system embryos. The low fraction of outer solar system material in Earth and Mars indicates the presence of a persistent dust-drift barrier in the disk, highlighting the specific pathway of rocky planet formation in the solar system.

Description, Late accretion and Late Heavy Bombardment impactors were from the same inner solar system population., Late accretion describes the final addition of Earth’s mass following Moon formation and includes a period of Late Heavy Bombardment (LHB), which occurred either as a short-lived cataclysm triggered by a late giant planet orbital instability or a declining bombardment during late accretion. Using genetically characteristic ruthenium and molybdenum isotope compositions of lunar impact–derived rocks, we show that the impactors during the LHB and the entire period of late accretion were the same type of bodies and that they originated in the terrestrial planet region. Because a cataclysmic LHB would have, in part, resulted in compositionally distinct projectiles, we conclude that the LHB reflects the tail end of accretion. This implies that the giant planet orbital instability occurred during the main phase of planet formation. Last, because of their inner solar system origin, late-accreted bodies cannot be the primary source of Earth’s water.

The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo, Ru, and Ni isotopic compositions that are intermediate between those of the non-carbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W chronology of Nedagolla indicates that this mixed NC-CC isotopic composition was established relatively late, more than 7 million years after Solar System formation. The mixed NC-CC isotopic composition is consistent with the chemical composition of Nedagolla, which combines signatures of metal segregation under more oxidizing conditions (relative depletions in Mo and W), characteristic for CC bodies, and more reducing conditions (high Si and Cr contents), characteristic for some NC bodies, in a single sample. These data combined suggest that Nedagolla formed as the result of collisional mixing of NC and CC core material, which partially re-equilibrated with silicate mantle material that predominantly derives from the NC body. These mixing processes might have occurred during a hit-and-run collision between two differentiated bodies, which also provides a possible pathway for Nedagolla's extreme volatile element depletion. As such, Nedagolla provides the first isotopic evidence for early collisional mixing of NC and CC bodies that is expected as a result of Jupiter's growth., Accepted for publication in Meteoritics & Planetary Science

The isotopic composition of meteorites and terrestrial planets holds important clues about the earliest history of the Solar System and the processes of planet formation. Recent work has shown that meteorites exhibit a fundamental isotopic dichotomy between non-carbonaceous (NC) and carbonaceous (CC) groups, which most likely represent material from the inner and outer Solar System, respectively. Here we review the isotopic evidence for this NC–CC dichotomy, discuss its origin and highlight the far-reaching implications for the dynamics of the solar protoplanetary disk. The NC–CC dichotomy combined with the chronology of meteorite parent-body accretion mandate an early and prolonged spatial separation of inner (NC) and outer (CC) disk reservoirs, lasting between ~1 and ~4 Myr after Solar System formation. This is most easily reconciled with the early and rapid growth of Jupiter’s core, inhibiting substantial exchange of material from inside and outside its orbit. The growth and migration of Jupiter also led to the later implantation of CC bodies into the inner Solar System and, therefore, can explain the co-occurrence of NC and CC bodies in the asteroid belt, and the delivery of volatile and water-rich CC bodies to the terrestrial planets. Cosmochemical measurements reveal the existence of two distinct reservoirs of non-carbonaceous and carbonaceous materials, originating from the inner and outer protoplanetary disk, respectively, which separated after the first million years after the birth of the Solar System, possibly due to the rapid growth of Jupiter’s core.

Non-magmatic iron meteorites, including the IIE group, can provide important insights into the history of metal-silicate differentiation and collisions on planetesimals. To better constrain the evolution of metal segregation and impacts on the IIE parent body, W isotopic data are reported for 10 IIE iron meteorites and a metal vein from the Portales Valley H6 chondrite. In addition, Pt isotopic data were obtained to quantify cosmic ray-induced neutron capture effects on W isotopes. After correction for these effects, the IIE iron meteorites exhibit variable pre-exposure 182W compositions, translating into Hf-W model age clusters of ∼4–5 million years (Ma), ∼10 Ma, ∼15 Ma, and ∼27 Ma after CAI formation. These distinct 182W clusters likely represent samples from several discrete metallic melt pools on the IIE parent asteroid. The earliest metal segregation event at ∼4–5 Ma was likely facilitated by 26Al decay as an internal heat source. By contrast, the younger Hf-W model ages may not be chronologically meaningful, and probably reflect the effects of secondary mixing and re-equilibration of metal and silicates, likely facilitated by impacts on the IIE parent body. Thus, contrary to prior work, the Hf-W systematics of IIE iron meteorites do not require a protracted history of metal-silicate separation on the IIE parent body. Instead the results of this study are fully consistent with a single partial metal-silicate differentiation event driven by endogenic heating at ∼4–5 Ma, followed by one or multiple impact events causing mixing and re-equilibration of metal and silicates at a later stage. The exact timing of these impact event(s) remains poorly constrained, but they most likely occurred in the first few tens of Ma of Solar System history.

Recent work has identified a nucleosynthetic isotope dichotomy between “carbonaceous” (CC) and “non-carbonaceous” (NC) meteorites. Here, we report new Ru isotope data for rare iron meteorite groups belonging to the NC and CC suites. We show that by studying the relative isotopic characteristics of Ru, Mo, and W in iron meteorites, it is possible to constrain the processes leading to the distinct isotope heterogeneities in both reservoirs. In NC meteorites, internally normalized, mass-independent isotope ratios of Mo and Ru are correlated, but those of Mo and W are not. In CC meteorites, Mo and W isotope ratios are correlated, but those of Mo and Ru are not; specifically, Mo isotopic compositions are variable and those of Ru are more restricted. The contrasting behaviors of Ru and W relative to Mo in the two reservoirs likely require processing of the presolar carriers under distinct redox conditions. This provides further evidence that NC and CC meteorites originated from spatially separated reservoirs that evolved under different prevailing conditions.

The Moon exhibits striking geological asymmetries in elevation, crustal thickness, and composition between its nearside and farside. Although several scenarios have been proposed to explain these asymmetries, their origin remains debated. Recent remote sensing observations suggest that (1) the crust on the farside highlands consists of two layers: a primary anorthositic layer with thickness of ~30-50 km and on top a more mafic-rich layer ~10 km thick; and (2) the nearside exhibits a large area of low-Ca pyroxene that has been interpreted to have an impact origin. These observations support the idea that the lunar nearside-farside asymmetries may be the result of a giant impact. Here, using quantitative numerical modeling, we test the hypothesis that a giant impact on the early Moon can explain the striking differences in elevation, crustal thickness, and composition between the nearside and farside of the Moon. We find that a large impactor, impacting the current nearside with a low velocity, can form a mega-basin and reproduce the characteristics of the crustal asymmetry and structures comparable to those observed on the current Moon, including the nearside lowlands and the farside's mafic-rich layer on top of a primordial anorthositic crust. Our model shows that the excavated deep-seated KREEP (potassium, rare-earth elements, and phosphorus) material, deposited close to the basin rim, slumps back into the basin and covers the entire basin floor; subsequent large impacts can transport the shallow KREEP material to the surface, resulting in its observed distribution. In addition, our model suggests that prior to the asymmetry-forming impact, the Moon may have had an 182W anomaly compared to the immediate post-giant impact Earth's mantle, as predicted if the Moon was created through a giant collision with the proto-Earth., 45 pages, 12 figures

Fifteen H, L, and LL ordinary chondrites of petrologic types 4–6 have been analyzed for Hf-W isotope systematics to constrain the chronology, internal structure, and thermal history of their parent bodies. For most samples coarse-grained metals plot below the isochrons defined by silicate-dominated fractions which consist of variable mixtures of silicate minerals with tiny metal inclusions. This offset results from an earlier Hf-W closure in the large metal grains and provides a new means for simultaneously determining cooling rates and Hf-W closure ages for individual samples. For most type 5 and 6 samples, cooling rates and Hf-W ages are inversely correlated, indicating that these samples derive from concentrically zoned bodies in which more strongly metamorphosed samples derive from greater depth. These data, therefore, provide strong evidence for a common ‘onion shell’ structure for the H, L, and LL chondrite parent bodies. The cooling rates and Hf-W ages of some type 5 and 6 chondrites overlap, indicating that the Hf-W systematics provide a more robust measure of the thermal history and burial depth of a given sample than the simple petrographic distinction between types 5 and 6. Two type 6 samples deviate from the correlation between cooling rates and Hf-W ages and cooled much faster than expected for their Hf-W age. These samples likely were excavated by impacts that occurred during high-temperature metamorphism and prior to complete closure of the Hf-W system at ∼10 Ma after CAI formation. As these impacts would have disturbed the asteroid’s cooling history, these samples likely derive from different bodies than samples with undisturbed cooling histories, implying that ordinary chondrites derive from more than just three parent bodies. The Hf-W data reveal that metal-silicate fractionation among the H, L, and LL groups occurred between ∼2 and ∼2.7 Ma after CAI formation and, hence, was about coeval to chondrule formation. As both metal-silicate fractionation and chondrule formation occurred prior to chondrite parent body accretion, there should be no ordinary chondrite chondrules that are younger than ∼2.7 Ma. Finally, ordinary chondrite precursors had lower Hf/W ratios than carbonaceous chondrites, suggesting that inner and outer solar system materials, respectively, were chemically distinct even for refractory elements.

Earth grew through collisions with Moon-sized to Mars-sized planetary embryos from the inner Solar System, but it also accreted material from greater heliocentric distances1,2, including carbonaceous chondrite-like bodies, the likely source of Earth’s water and highly volatile species3,4. Understanding when and how this material was added to Earth is critical for constraining the dynamics of terrestrial planet formation and the fundamental processes by which Earth became habitable. However, earlier studies inferred very different timescales for the delivery of carbonaceous chondrite-like bodies, depending on assumptions about the nature of Earth’s building materials5–11. Here we show that the Mo isotopic composition of Earth’s primitive mantle falls between those of the non-carbonaceous and carbonaceous reservoirs12–15, and that this observation allows us to quantify the accretion of carbonaceous chondrite-like material to Earth independently of assumptions about its building blocks. As most of the Mo in the primitive mantle was delivered by late-stage impactors10, our data demonstrate that Earth accreted carbonaceous bodies late in its growth history, probably through the Moon-forming impact. This late delivery of carbonaceous material probably resulted from an orbital instability of the gas giant planets, and it demonstrates that Earth’s habitability is strongly tied to the very late stages of its growth. Measurements of Mo in meteorites constrain the time when the Earth accreted carbonaceous material from the outer Solar System (a likely source of Earth’s water and volatiles) to late in the Earth’s growth history—probably in the same event that formed the Moon.

The 182Hf-182W chronology of iron meteorites provides crucial information on the timescales of accretion and differentiation of some of the oldest planetesimals of the Solar System. Determining accurate Hf-W model ages of iron meteorites requires correction for cosmic ray expo-sure (CRE) induced modifications of W isotope compositions, which can be achieved using in-situ neutron dosimeters such as Pt isotopes. Until now it has been assumed that all Pt isotope variations in meteorites reflect CRE, but here we show that some ungrouped iron meteorites display small nucleosynthetic Pt isotope anomalies. These provide the most appropriate starting composition for the correction of CRE-induced W isotope variations in iron meteorites from all major chemical groups, which leads to a ~1 Ma upward revision of previously reported Hf-W model ages. The revised ages indicate that core formation in non-carbonaceous (NC) iron meteorite parent bodies occurred at ~1-2 Ma after CAI formation, whereas most carbonaceous (CC) iron meteorite parent bodies underwent core formation ~2 Ma later. We show that the younger CC cores have lower Fe/Ni ratios than the earlier-formed NC cores, indicating that core formation under more oxidizing conditions occurred over a more protracted timescale. Thermal modeling of planetesimals heated by 26Al-decay reveals that this protracted core formation timescale is consistent with a higher fraction of water ice in CC compared to NC planetesimals, implying that in spite of distinct core formation timescales, NC and CC iron meteorite parent bodies accreted about contemporaneously within ~1 Ma after CAI formation, but at different radial locations in the disk., Accepted for publication in Earth and Planetary Science Letters

The last thirty years of cosmochemistry and planetary science have shown that one major Solar System reservoir is vastly undersampled in the available suite of extra-terrestrial materials, namely small bodies that formed in the outer Solar System (>10 AU). Because various dynamical evolutionary processes have modified their initial orbits (e.g., giant planet migration, resonances), these objects can be found today across the entire Solar System as P/D near-Earth and main-belt asteroids, Jupiter and Neptune Trojans, comets, Centaurs, and small (diameter < 200 km) trans-Neptunian objects. This reservoir is of tremendous interest, as it is recognized as the least processed since the dawn of the Solar System and thus the closest to the starting materials from which the Solar System formed. Some of the next major breakthroughs in planetary science will come from studying outer Solar System samples (volatiles and refractory constituents) in the laboratory. Yet, this can only be achieved by an L-class mission that directly collects and returns to Earth materials from this reservoir. It is thus not surprising that two White Papers advocating a sample return mission of a primitive Solar System small body (ideally a comet) were submitted to ESA in response to its Voyage 2050 call for ideas for future L-class missions in the 2035-2050 time frame. One of these two White Papers is presented in this article., Experimental Astronomy, 54 (2-3), ISSN:0922-6435, ISSN:1572-9508

Nucleosynthetic Fe isotopic anomalies in meteorites may be used to reconstruct the early dynamical evolution of the solar system and to identify the origin and nature of the material that built planets. Using high-precision iron isotopic data of 23 iron meteorites from nine major chemical groups we show that all iron meteorites show the same fundamental dichotomy between non-carbonaceous (NC) and a carbonaceous (CC) meteorites previously observed for other elements. The Fe isotopic anomalies are predominantly produced by variation in 54Fe, where all CC iron meteorites are characterized by an excess in 54Fe relative to NC iron meteorites. This excess in 54Fe is accompanied by an excess in 58Ni observed in the same CC meteorite groups. Together, these overabundances of 54Fe and 58Ni are produced by nuclear statistical equilibrium either in type Ia supernovae or in the Si/S shell of core-collapse supernovae. The new Fe isotopic data reveal that Earth's mantle plots on or close to correlations defined by Fe, Mo, and Ru isotopic anomalies in iron meteorites, indicating that throughout Earth's accretion, the isotopic composition of its building blocks did not drastically change. While Earth's mantle has a similar Fe isotopic composition to CI chondrites, the latter are clearly distinct from Earth's mantle for other elements (e.g., Cr and Ni) whose delivery to Earth coincided with Fe. The fact that CI chondrites exhibit large Cr and Ni isotopic anomalies relative to Earth's mantle, therefore, demonstrates that CI chondrites are unlikely to have contributed significant Fe to Earth., Comment: 1 Table, 9 Figures

Compared to the composition of CI chondrites and the Sun, all other carbonaceous chondrites are variably depleted in volatile elements. However, the origin of these depletions, and how they are related to volatile loss during high-temperature processes within the solar nebula, are unclear. To better understand the processes that caused volatile element fractionations among carbonaceous chondrites, we obtained mass-dependent Te isotopic compositions and Te concentrations for a comprehensive set of samples from the major carbonaceous chondrite groups. The chondrites exhibit well-resolved inter-group Te isotope variations towards lighter isotopic compositions for increasingly volatile-depleted samples. The Te isotopic compositions and concentrations are also correlated with the mass fraction of matrix and with nucleosynthetic e 54 Cr anomalies. Combined, these correlations indicate mixing between volatile-rich, isotopically heavy, and 54Cr-rich CI-like matrix with volatile-poor, isotopically light, and 54Cr-poorer chondrules or chondrule precursors. The Te-Cr isotopic correlation suggests that all carbonaceous chondrites contain CI-like matrix, and that chondrules and this CI-like matrix formed from isotopically distinct material originating from different regions of the disk. The only samples plotting off the Te-Cr correlation are CR chondrites, indicating that CR chondrules formed from different precursor material than chondrules from other carbonaceous chondrites, either because they formed at greater heliocentric distance and/or at a later time. Plots of volatile element abundances versus matrix mass fraction reveal that chondrules/chondrule precursors display CI-chondritic ratios for volatile elements with 50% condensation temperatures below ∼750 K, with an overall abundance of ∼0.13 × CI. Mixing between these two components, therefore, naturally results in CI-like ratios for these elements in all carbonaceous chondrites, in spite of different degrees of volatile depletion. A corollary of this observation is that the CI-like ratios of volatile elements in the bulk silicate Earth may result from the accretion of volatile-depleted materials and do not require accretion of CI chondrites themselves.