¹Maxime Piralla,¹Johan Villeneuve,¹Nicolas Schnuriger,¹David V.Bekaert,¹Yves Marrocchi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115427]
¹Université de Lorraine, CNRS, CRPG, UMR 7358, Nancy, France
Copyright Elsevier

The chronology of dust formation in the early solar system remains controversial. Chondrules are the most abundant high-temperature objects formed during the evolution of the circumsolar disk. Considering chondrule formation, absolute lead‑lead (Pbsingle bondPb) ages and aluminum‑magnesium (26Alsingle bond26Mg) ages relative to calcium‑aluminum-rich inclusions (CAIs) provide inconsistent chronologies, with Pbsingle bondPb ages showing early and protracted chondrule formation episodes whereas 26Alsingle bond26Mg ages suggest that chondrule production was delayed by >1.5 Ma. Here, we develop a new method to precisely determine in situ 26Alsingle bond26Mg ages of spinel-bearing chondrules without being affected by secondary asteroidal processes. Our data demonstrate that 26Alsingle bond26Mg chondrule formation ages are actually 1 Ma older than previously thought and extend over the entire lifetime of the disk. This shift in chondrule formation ages relative to CAIs, however, is not sufficient to reconcile the Pbsingle bondPb and 26Alsingle bond26Mg chronologies. Thus, either chondrules Pbsingle bondPb ages and volcanic achondrites 26Alsingle bond26Mg ages are incorrect or the age of the solar system age should be reevaluated at 4568.7 Ma to ensure consistency between chronometers. We favor the second hypothesis, given that (i) the canonical age of CAIs was determined using only 4 specimens and (ii) older ages of 4568.2 Ma have also been measured. We show that the adoption of 4568.7 Ma as the new canonical age of CAIs and the use of our new spinel-derived 26Alsingle bond26Mg ages enable reconciling the Pbsingle bondPb and 26Alsingle bond26Mg ages of chondrules and achondrites. This new chronology implies the existence of a 0.7–1 Ma gap between the formation of refractory inclusions and chondrules, and supports the homogeneous distribution of 26Al in the circumsolar disk.

^1,2,3Queenie H. S. Chan,⁴Jonathan S. Watson,⁴Mark A. Sephton,^3,5,6Áine C. O’Brien,⁵Lydia J. Hallis
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13936]
¹Royal Holloway University of London, Surrey, TW20 0EX UK
²The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
³UK Fireball Network (UKFN), UK
⁴Department of Earth Science and Engineering, Imperial College London, London, SW7 2BX UK
⁵School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ UK
⁶UK Fireball Alliance (UKFAll), UK
Published by arrangement with John Wiley & Sons

The rapid recovery of the Winchcombe meteorite offers a valuable opportunity to study the soluble organic matter (SOM) profile in pristine carbonaceous astromaterials. Our interests in the biologically relevant molecules, amino acids—monomers of protein, and the most prevalent meteoritic organics—polycyclic aromatic hydrocarbons (PAHs) are addressed by analyzing the solvent extracts of a Winchcombe meteorite stone using gas chromatography mass spectrometry. The Winchcombe sample contains an amino acid abundance of ~1132 parts-per-billion that is about 10 times lower than other CM2 meteorites. The detection of terrestrially rare amino acids, including α-aminoisobutyric acid (AIB); isovaline; β-alanine; α-, β-, and γ-amino-n-butyric acids; and 5-aminopentanoic acid, and the racemic enantiomeric ratios (D/L = 1) observed for alanine and isovaline indicate that these amino acids are indigenous to the meteorite and not terrestrial contaminants. The presence of predominantly α-AIB and isovaline is consistent with their formation via the Strecker-cyanohydrin synthetic pathway. The L-enantiomeric excesses in isovaline previously observed for aqueously altered meteorites were viewed as an indicator of parent body aqueous processing; thus, the racemic ratio of isovaline observed for Winchcombe, alongside the overall high free:total amino acid ratio, and the low amino acid concentration suggest that the analyzed stone is derived from a lithology that has experienced brief episode(s) of aqueous alteration. Winchcombe also contains 2- to 6-ring alkylated and nonalkylated PAHs. The low total PAHs abundance (6177 ppb) and high nonalkylated:alkylated ratio are distinct from that observed for heavily aqueously altered CMs. The weak petrographic properties of Winchcombe, as well as the discrepancies observed for the Winchcombe SOM content—a low total amino acid abundance comparable to heavily altered CMs, and yet the high free:total amino acid and nonalkylated:alkylated PAH ratios are on par with the less altered CMs—suggest that Winchcombe could represent a class of weak, poorly lithified meteorite not been previously studied.