Astronomical context of Solar System formation from molybdenum isotopes in meteorite inclusions

Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years

Terrestrial planet formation from lost inner solar system material

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

Replication Data for: No 182W evidence for early Moon formation

Abstract: The Moon-forming giant impact was probably the last major event in Earth’s accretion, so dating this event is critical to determine the timeline of terrestrial planet formation. Recently, Thiemens et al. ( https://doi.org/10.1038/s41561-019-0398-3) used the short-lived 182Hf–182W system to argue that the Moon formed within the first 60 Myr of Solar System history. Here we demonstrate, however, that mixing processes during and after the giant impact modified the 182W compositions of the Earth and Moon, which hampers the use of the Hf–W system to date the Moon. Our results show that the lunar 182W record is fully consistent with a recently determined, younger age of the Moon of 142 ± 25 Myr after Solar System formation (Maurice et al., Adv. 6, eaba8949, 2020

Replication Data for: No 182W evidence for early Moon formation

Abstract: The Moon-forming giant impact was probably the last major event in Earth’s accretion, so dating this event is critical to determine the timeline of terrestrial planet formation. Recently, Thiemens et al. ( https://doi.org/10.1038/s41561-019-0398-3) used the short-lived 182Hf–182W system to argue that the Moon formed within the first 60 Myr of Solar System history. Here we demonstrate, however, that mixing processes during and after the giant impact modified the 182W compositions of the Earth and Moon, which hampers the use of the Hf–W system to date the Moon. Our results show that the lunar 182W record is fully consistent with a recently determined, younger age of the Moon of 142 ± 25 Myr after Solar System formation (Maurice et al., Adv. 6, eaba8949, 2020

Replication Data for: No 182W evidence for early Moon formation

Abstract: The Moon-forming giant impact was probably the last major event in Earth’s accretion, so dating this event is critical to determine the timeline of terrestrial planet formation. Recently, Thiemens et al. ( https://doi.org/10.1038/s41561-019-0398-3) used the short-lived 182Hf–182W system to argue that the Moon formed within the first 60 Myr of Solar System history. Here we demonstrate, however, that mixing processes during and after the giant impact modified the 182W compositions of the Earth and Moon, which hampers the use of the Hf–W system to date the Moon. Our results show that the lunar 182W record is fully consistent with a recently determined, younger age of the Moon of 142 ± 25 Myr after Solar System formation (Maurice et al., Adv. 6, eaba8949, 2020

Cosmogenic 180W variations in meteorites and re-assessment of a possible 184Os–180W decay system

We measured tungsten (W) isotopes in 23 iron meteorites and the metal phase of the CB chondrite Gujba in order to ascertain if there is evidence for a large-scale nucleosynthetic heterogeneity in the p-process isotope 180W in the solar nebula as recently suggested by Schulz et al. (2013). We observed large excesses in 180W (up to ≈ 6 ε) in some irons. However, significant within-group variations in magmatic IIAB and IVB irons are not consistent with a nucleosynthetic origin, and the collateral effects on 180W from an s-deficit in IVB irons cannot explain the total variation. We present a new model for the combined effects of spallation and neutron capture reactions on 180W in iron meteorites and show that at least some of the observed within-group variability is explained by cosmic ray effects. Neutron capture causes burnout of 180W, whereas spallation reactions lead to positive shifts in 180W. These effects depend on the target composition and cosmic-ray exposure duration; spallation effects increase with Re/W and Os/W ratios in the target and with exposure age. The correlation of 180W/184W with Os/W ratios in iron meteorites results in part from spallogenic production of 180W rather than from 184Os decay, contrary to a recent study by Peters et al. (2014). Residual ε180W excesses after correction for an s-deficit and for cosmic ray effects may be due to ingrowth of 180W from 184Os decay, but the magnitude of this ingrowth is at least a factor of ≈2 smaller than previously suggested. These much smaller effects strongly limit the applicability of the putative 184Os-180W system to investigate geological problems

Replication Data for: Age of Jupiter inferred from the distinct genetics and formation times of meteorites.

Jupiter is the most massive planet of the Solar System and its presence had an immense effect on the dynamics of the solar accretion disk. Knowing the age of Jupiter, therefore, is key for understanding how the Solar System evolved toward its present-day architecture. However, although models predict that Jupiter formed relatively early, until now, its formation has never been dated. Here we show through isotope analyses of meteorites that Jupiter’s solid core formed within only ∼1 My after the start of Solar System history, making it the oldest planet. Through its rapid formation, Jupiter acted as an effective barrier against inward transport of material across the disk, potentially explaining why our Solar System lacks any super-Earths

The abundance and isotopic composition of Cd in iron meteorites

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility-controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of 113Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd-Pt-W isotope results from this study thus demonstrate that the relative magnitude of neutron capture-induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites