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We report C, N, Mg-Al, Si, and S isotope data of six 1–3 μm-sized SiC grains of Type X from the Murchison CM2 chondrite, believed to have formed in the ejecta of core-collapse supernova (CCSN) explosions. Their C, N, and Si isotopic compositions are fully compatible with previously studied X grains. Magnesium is essentially monoisotopic 26Mg which gives clear evidence for the decay of radioactive 26Al. Inferred initial 26Al/27Al ratios are between 0.6 and 0.78 which is at the upper end of previously observed ratios of X grains. Contamination with terrestrial or solar system Al apparently is low or absent, which makes the X grains from this study particularly interesting and useful for a quantitative comparison of Al isotope data with predictions from supernova models. The consistently high 26Al/27Al ratios observed here may suggest that the lower 26Al/27Al ratios of many X grains from the literature are the result of significant Al contamination and in part also of an improper quantification of 26Al. The real dispersion of 26Al/27Al ratios in X grains needs to be explored by future studies. The high observed 26Al/27Al ratios in this work provide a crucial constraint for the production of 26Al in CCSN models. We explored different CCSN models, including both “classical” and H ingestion CCSN models. It is found that the classical models cannot account for the high 26Al/27Al ratios observed here; in contrast, H ingestion models are able to reproduce the 26Al/27Al ratios along with C, N, and Si isotopic ratios reasonably well.

Comets are considered the most primitive planetary bodies in our Solar System, i.e., they should have best preserved the solid components of the matter from which our Solar System formed. ESA’s recent Rosetta mission to Jupiter family comet 67P/Churyumov–Gerasimenko (67P/CG) has provided a wealth of isotope data which expanded the existing data sets on isotopic compositions of comets considerably. In this paper we review our current knowledge on the isotopic compositions of H, C, N, O, Si, S, Ar, and Xe in primitive Solar System materials studied in terrestrial laboratories and how the Rosetta data acquired with the ROSINA (Rosetta Orbiter Sensor for Ion and Neutral Analysis) and COSIMA (COmetary Secondary Ion Mass Analyzer) mass spectrometer fit into this picture. The H, Si, S, and Xe isotope data of comet 67P/CG suggest that this comet might be particularly primitive and might have preserved large amounts of unprocessed presolar matter. We address the question whether the refractory Si component of 67P/CG contains a presolar isotopic fingerprint from a nearby Type II supernova (SN) and discuss to which extent C and O isotope anomalies originating from presolar grains should be observable in dust from 67P/CG. Finally, we explore whether the isotopic fingerprint of a potential late SN contribution to the formation site of 67P/CG in the solar nebula can be seen in the volatile component of 67P/CG.

We have analyzed molybdenum, ruthenium, and barium isotopes simultaneously in 55 individual presolar silicon carbide (SiC) grains from the Murchison CM2 meteorite using the Chicago Instrument for Laser Ionization (or CHILI). Most grains show clear s-process signatures, which are strongly correlated for molybdenum and ruthenium. For all three elements, we provide estimates for s-process contributions from low-mass AGB stars with unprecedented precision. Variations in s-process production observed for some nuclides reflect a strong dependence on physical properties, neutron density, temperature, and timing, affecting various s-process branch points. Significant contamination can be excluded for a majority of grains. Instead, distributions along mixing lines in three-isotope diagrams reflect mixing between initial parent star material and matter synthesized in the star. The results suggest that the ratios between p- and r-process isotopes of molybdenum, ruthenium, and barium in presolar SiC from many parent stars are the same as the ones inferred for the solar system. This indicates that the products of these processes were well mixed by the time the molecular cloud collapsed to form the stars that eventually grew the SiC grains, and that this mixture did not change between formation of the precursor stars and formation of the Sun.

The Presolar Grain Database (PGD) contains the vast majority of isotope data (published and unpublished) on presolar grains and was first released as a collection of spreadsheets in 2009. It has been a helpful tool used by many researchers in cosmochemistry and astrophysics. However, over the years, accumulated errors compromised major parts of the PGD. Here, we provide a fresh start, with the PGD for silicon carbide (SiC) grains rebuilt from the ground up. We also provide updated rules for SiC grain type classification to unify previous efforts, taking into account newly discovered grain types. We also define a new grain type D, which includes some grains previously classified as ungrouped. Future work will focus on rebuilding the PGD for other kinds of presolar grains: graphite, oxides, silicates, and rarer phases.

We measured the nickel isotope composition of troilites from chondritic meteorites using the NanoSIMS to put constraints on the abundance of iron-60 in the early solar system. The troilites were selected from petrologic type 3 ordinary and carbonaceous chondrites. Based on petrographic observations and mineral chemistry, the troilites targeted for isotope analysis crystallized from melts, most likely in a nebular setting. Our isotope analyses did not reveal any significant correlation between nickel-60 enrichments and Fe/Ni ratios, either in the entire set of troilite grains or in individual troilites. The average inferred initial 60Fe/56Fe ratio of the studied troilites (i.e., the 60Fe/56Fe ratio calculated for the entire troilite population) is 1.05 (±1.48) ×10−8. This value is very similar to those estimated in the past for Semarkona chondrules, angrites, as well as diogenites and eucrites, based on the isotope analyses of bulk samples (10−9–10−8), but about two orders of magnitude smaller than the average initial 60Fe/56Fe ratios inferred previously for Semarkona troilites and many chondrules from ordinary and carbonaceous chondrites (10−7–10−6) using in situ analysis techniques. Based on petrographic evidence, and the generally unequilibrated nature of our samples, as well as on the timing of chondrule formation and planetary evolution, the lack of discernible signs of in situ iron-60 decay in the studied troilites is probably unrelated to metamorphic re-equilibration, and it is also not the result of a late formation of the troilites. We suggest that the highest inferred initial 60Fe/56Fe ratios reported in the literature are probably inaccurate.

The abundance of iron-60 in the early solar system is important for planetary evolution models, and has been hotly debated. To put further constraints on the initial 60Fe/56Fe ratio of the solar system, here we present new iron-nickel isotope data, measured in situ by NanoSIMS, for 14 silicate chondrules from three carbonaceous and three unequilibrated ordinary chondrites. NanoSIMS measurements were performed at high spatial resolution (200–300 nm primary beam diameter), to avoid inclusion of unwanted phases in the analysis volume. The average initial 60Fe/56Fe ratios that can be estimated from our pooled chondrule data are 2.1 (±1.3) × 10−7 and 0.8 (±1.0) × 10−7 for carbonaceous and ordinary chondrites, respectively (1σ uncertainties). The estimated average initial 60Fe/56Fe ratio of all analyzed chondrules is 1.0 (±0.7) × 10−7. These results are inconsistent with initial 60Fe/56Fe ratios >2.4 × 10−7 (2σ upper limit of our entire data set) reported in the literature for some chondrule silicates based on in situ isotope data, and agree better with our previously published in situ data on chondritic troilites (0.10 ± 0.15 × 10−7), as well as with 60Fe/56Fe ratios estimated from isotope data of bulk meteorites and chondrules (0.10–0.75 × 10−7). Our isotope data hint at a possible difference between the initial 60Fe/56Fe ratios of the early solar system’s two major isotope reservoirs, with the carbonaceous chondritic reservoir having higher iron-60 abundance than the non-carbonaceous reservoir. Nevertheless, in light of similar hints in the literature, this possibility deserves further investigation.

Global sulfate production plays a key role in aerosol radiative forcing; more than half of this production occurs in clouds. We found that sulfur dioxide oxidation catalyzed by natural transition metal ions is the dominant in-cloud oxidation pathway. The pathway was observed to occur primarily on coarse mineral dust, so the sulfate produced will have a short lifetime and little direct or indirect climatic effect. Taking this into account will lead to large changes in estimates of the magnitude and spatial distribution of aerosol forcing. Therefore, this oxidation pathway-which is currently included in only one of the 12 major global climate models-will have a significant impact on assessments of current and future climate.

Primitive Solar System materials host small amounts of refractory dust grains predating the formation of the Sun and its planetary system. These ‘presolar’ grains condensed in the ejecta of evolved stars, novae and supernovae1. Their highly anomalous isotopic compositions cannot be explained by chemical or physical processes within the Solar System; instead, they represent the nucleosynthetic signatures of their stellar parents. Among this ‘true stardust’, silicates are the most abundant type of dust available for single-grain analyses2, with typical sizes of approximately 150 nm (ref. 3). Unlike presolar silicon carbides, aluminium oxides or graphites, which can be separated chemically from meteorites, presolar silicates have to be identified in situ, as they would be destroyed by extraction agents. Instrumental restrictions have constrained almost all previous magnesium isotopic measurements to presolar aluminium oxides, and the contribution of radiogenic 26Mg from 26Al decay has precluded unambiguous conclusions about their initial magnesium isotopes. Recent technical advances have enabled the undisturbed in situ investigation of magnesium isotopes in presolar silicates with unprecedented spatial resolution (<150 nm). Here we show that a minor but important fraction of silicate stardust believed to come from red giant stars has a supernova origin instead, if hydrogen ingestion occurred during the pre-supernova phase, making the supernova dust fraction among >200-nm-sized presolar silicates significantly higher than previously inferred1.A minor but important fraction of silicate stardust believed to come from red giant stars is shown to have a supernova origin instead, making the supernova dust fraction among >200-nm-sized presolar silicates significantly higher than previously inferred.

EISCAT VHF radar data are used for observing, monitoring, and understanding Earth’s upper atmosphere. This paper presents an approach to segment Polar Mesospheric Summer Echoes (PMSE) from datasets obtained from EISCAT VHF radar data. The data consist of 30 observations days, corresponding to 56,250 data samples. We manually labeled the data into three different categories: PMSE, Ionospheric background, and Background noise. For segmentation, we employed random forests on a set of simple features. These features include: altitude derivative, time derivative, mean, median, standard deviation, minimum, and maximum values corresponding to neighborhood sizes ranging from 3 by 3 to 11 by 11 pixels. Next, in order to reduce the model bias and variance, we employed a method that decreases the weight applied to pixel labels with large uncertainty. Our results indicate that, first, it is possible to segment PMSE from the data using random forests. Second, the weighted-down labels technique improves the performance of the random forests method.

Presolar graphite grains carry the isotopic signatures of their parent stars. A significant fraction of presolar graphites show isotopic abundance anomalies relative to solar for elements such as O, Si, Mg, and Ca, which are compatible with nucleosynthesis in core-collapse supernovae (CCSNe). Therefore, they must have condensed from CCSN ejecta before the formation of the Sun. Their most puzzling abundance signature is the 22Ne-enriched component Ne-E(L), interpreted as the effect of the radioactive decay of 22Na (T1/2 = 2.6 yr). Previous works have shown that if H is ingested into the He shell and not fully destroyed before the explosion, the CCSN shock in the He-shell material produces large amounts of 22Na. Here we focus on such CCSN models, showing a radioactive 26Al production compatible with grain measurements, and analyze the conditions of 22Na nucleosynthesis. In these models, 22Na is mostly made in the He shell, with a total ejected mass varying between 2.6 × 10−3 M⊙ and 1.9 × 10−6 M⊙. We show that such 22Na may already impact the CCSN light curve 500 days after the explosion, and at later stages it can be the main source powering the CCSN light curve for up to a few years before 44Ti decay becomes dominant. Based on the CCSN yields above, the 1274.53 keV γ-ray flux due to 22Na decay could be observable for years after the first CCSN light is detected, depending on the distance. This makes CCSNe possible sites to detect a 22Na γ-ray signature consistently with the Ne-E(L) component found in presolar graphites. Finally, we discuss the potential contribution from 22Na decay to the Galactic positron annihilation rate.