¹R.Brunetto et al. (>10)
The Astrophysical Journal Letters 951, L33 Open Access Link to Article [DOI 10.3847/2041-8213/acdf5c]
¹1 IAS, Université Paris-Saclay, CNRS, France; rosario.brunetto@universite-paris-saclay.fr

Ryugu is a second-generation C-type asteroid formed by the reassembly of fragments of a previous larger body in the main asteroid belt. While the majority of Ryugu samples returned by Hayabusa2 are composed of a lithology dominated by aqueously altered minerals, clasts of pristine olivine and pyroxene remain in the least-altered lithologies. These clasts are objects of great interest for revealing the composition of the dust from which the original building blocks of Ryugu’s parent asteroid formed. Here we show that some grains rich in olivine, pyroxene, and amorphous silicates discovered in one millimeter-sized stone of Ryugu have infrared spectra similar to the D-type asteroid Hektor (a Jupiter Trojan), to comet Hale–Bopp, and to some anhydrous interplanetary dust particles of probable cometary origin. This result indicates that Ryugu’s primary parent body incorporated anhydrous ingredients similar to the building blocks of asteroids (and possibly some comets) formed in the outer solar system, and that Ryugu retained valuable information on the formation and evolution of planetesimals at different epochs of our solar system’s history.

^1,2Martin Bizarro et al. (>10)
The Astrophysical Journal Letters 958, L25 Open Access Link to Article [DOI 10.3847/2041-8213/ad09d9]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, DK-1350 Copenhagen K, Denmark; bizzarro@sund.ku.dk
²Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ26Mg* and μ25Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ25Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ25Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ25Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ26Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ26Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26Al given their respective 27Al/24Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26Al/27Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.

¹Yves Marrocchi,^1,2Maxime Piralla,³François L. H. Tissot
The Astrophysical Journal Letters 954, L27 Open Access Link to Article [DOI 10.3847/2041-8213/acefd1]
¹Centre de recherches pétrographiques et géochimiques (CRPG), CNRS, UMR 7358, F-54000, Nancy, France; yvesm@crpg.cnrs-nancy.fr
²Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
³The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA

The recent advent of nontraditional isotopic systems has revealed that meteorites display a fundamental isotopic dichotomy between noncarbonaceous (NC) and carbonaceous (C) groups, which represent material from the inner and outer solar system, respectively. On the basis of iron isotope anomalies, this view has recently been challenged in favor of a circumsolar disk structured into three distinct reservoirs (the so-called isotopic trichotomy). In this scenario, the CI chondrites—a rare type of carbonaceous chondrites with chemical composition similar to that of the Sun’s photosphere—would sample a distinct source region than other carbonaceous chondrites, located beyond Saturn’s orbit. Here, we report a model based on the available data for both mass-dependent fractionation of Te stable isotopes and mass-independent Fe nucleosynthetic anomalies. On the basis of the Te–Fe isotopic correlation defined by all carbonaceous chondrites including CIs, we show that the NC-CC dichotomy extends to Fe isotopes. Our finding thus supports (i) the existence of only two reservoirs in the early solar system and (ii) the ubiquitous presence of CI-like dust throughout the carbonaceous reservoir. Our approach also reveals that the carrier phase of 54Fe anomalies corresponds to Fe–Ni metal beads mostly located within chondrules. Finally, we propose that the CC chondrule component records a constant mix of refractory inclusions and NC-like dust.