¹Karina López García,¹Tetsuya Yokoyama,¹Ikshu Gautam,¹Makiko K. Haba,²Tsuyoshi Iizuka,¹Nao Nakanishi,³Ryota Fukai
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70109]
¹Department of Earth and Planetary Science, Institute of Science Tokyo, Tokyo, Japan
²Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
³Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa, Japan
Published by arrangement with John Wiley & Sons

Ryugu materials closely resemble CI chondrites’ mineralogical, chemical, andisotopic compositions; yet minor but resolvable differences in certain elemental abundances areevident. In this study, the bulk chemical compositions of eight individual Ryugu particles(1.5–4.3 mg) from the first touchdown site (TD1) were determined using triple–quadrupoleinductively coupled plasma mass spectrometry (TQ-ICP-MS). These samples show broadabundance ranges (0.4–4 9 CI) for elements commonly hosted in minor secondary phasesincluding P, Ca, Mn, Sr, Y, Ba, and rare earth elements (REE), and display distinctcovariation patterns among these elements. Combining our data with previous analyses of TD1 Ryugu particles, we identified three compositional types: Type 1 particles are enriched by>20% in P, Ca, Mn, Sr, and REE relative to the Ryugu average; Type 3 particles are depletedby >20% in these elements but show slight enrichments (up to 30%) in siderophile andchalcophile elements; Type 2 particles have most elemental abundances within 20% of theRyugu average. These wide abundance ranges reflect heterogeneous distribution (nugget effect)of minor secondary minerals within Ryugu’s parent body. Such heterogeneity provides insightsinto the evolving conditions of alteration fluids and the consequent elemental fractionationpatterns.

¹Allison A. Baczynski et al. (>10)
Proceedings of the National Academy of Sciences of the USA (PNAS) 123, e2517723123 Open Access Link to Article [https://doi.org/10.1073/pnas.2517723123]
¹Department of Geosciences, Pennsylvania State University, University Park, PA 16802

Samples collected from the carbonaceous near-Earth asteroid Bennu and delivered to Earth by NASA’s OSIRIS-REx mission contain organic molecules relevant to prebiotic chemistry. Stable isotopic measurements of extraterrestrial soluble organic matter provide critical insights into the formation pathways and alteration histories of such molecules, which hold significance for understanding the origins of life. We leverage state-of-the-art techniques for picomolar-scale isotopic analyses of amino acids in samples of Bennu and, for comparison, the carbonaceous meteorite Murchison. We report intramolecular δ13C values for glycine, which have not previously been measured in extraterrestrial materials; molecular-averaged δ13C values for amino acids, aldehydes, and ketones; and δ15N values for glycine, β-alanine, and D/L-glutamic acid. Intramolecular carbon isotope patterns of glycine in Bennu contrast with those in Murchison, suggesting distinct formation pathways. We explore several formation mechanisms and hypothesize that the observed glycine in Murchison formed dominantly by a Strecker-like synthesis under aqueous conditions, whereas the glycine currently found in Bennu may have formed mainly by modified radical–radical reactions in primordial ices at the cold, outer reaches of the early Solar System and retained its isotopic values throughout accretion and multiple episodes of aqueous alteration. This hypothesis is supported by the highly 15N-enriched δ15N values in Bennu amino acids (+170 to 277‰). Differences in the δ15N values of D- and L-glutamic acid (Δ = 87‰) in Bennu affirm published reports of enantiomeric differences in meteoritic amino acids and challenge the assumption of isotopic uniformity between amino acid chiral pairs.