Meteorites & Asteroids

Origin Of Isotopic Diversity Among Carbonaceous Chondrites

By Keith Cowing
Status Report
March 8, 2023
Filed under , , , , , ,
Origin Of Isotopic Diversity Among Carbonaceous Chondrites
Cartoon illustrating our preferred scenario for transport and mixing of dust components before and during the accretion of the carbonaceous chondrite parent bodies. Based on model of Nanne et al. (2019) for the formation of the NC-CC dichotomy by time-varied infall from heterogenous molecular cloud core. A) Early infall had a CAI/AOA-like isotopic composition (blue), which reflects the isotopic composition of the early disk formed by viscous spreading. CAIs and AOAs are transported outward by the same process. B) Isotopic composition of the infall changes to NC-like (red), which dominates the inner disk. Chondrule precursors form in the inner disk and, like CAIs and AOAs, are transported outwards through the disk. After infall stopped, the disk exhibits an isotopic gradient from NC-like in the inner disk to CAI/AOA-like material in the outer disk. Mixing between these distinct materials in the inner disk then produced the characteristic isotopic composition of the CC reservoir. C) Radial drift of CAIs, AOAs, and chondrule precursors leads to their coupled enrichment in a pressure maximum, which is likely associated with the water ice line and the ultimate formation location of Jupiter. Chondrule formation and mixing of CAIs/AOAs, chondrules, and CI-like matrix occurs in this pressure trap, where the relative proportions of these components vary depending on the timing of parent body accretion. — astro-ph.EP

Carbonaceous chondrites are some of the most primitive meteorites and derive from planetesimals that formed a few million years after the beginning of the solar system.

Here, using new and previously published Cr, Ti, and Te isotopic data, we show that carbonaceous chondrites exhibit correlated isotopic variations that can be accounted for by mixing among three major constituents having distinct isotopic compositions, namely refractory inclusions, chondrules, and CI chondrite-like matrix.

The abundances of refractory inclusions and chondrules are coupled and systematically decrease with increasing amount of matrix. We propose that these correlated abundance variations reflect trapping of chondrule precursors, including refractory inclusions, in a pressure maximum in the disk, which is likely related to the water ice line and the ultimate formation location of Jupiter.

The variable abundance of refractory inclusions/chondrules relative to matrix is the result of their distinct aerodynamical properties resulting in differential delivery rates and their preferential incorporation into chondrite parent bodies during the streaming instability, consistent with the early formation of matrix-poor and the later accretion of matrix-rich carbonaceous chondrites.

Our results suggest that chondrules formed locally from isotopically heterogeneous dust aggregates which themselves derive from a wide area of the disk, implying that dust enrichment in a pressure trap was an important step to facilitate the accretion of carbonaceous chondrite parent bodies or, more generally, planetesimals in the outer solar system.

Jan L. Hellmann, Jonas M. Schneider, Elias Wölfer, Joanna Drążkowska, Christian A. Jansen, Timo Hopp, Christoph Burkhardt, Thorsten Kleine

Comments: 12 pages, 4 figures, 1 table. Accepted for publication in ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2303.04173 [astro-ph.EP] (or arXiv:2303.04173v1 [astro-ph.EP] for this version)
Submission history
From: Jan Hellmann
[v1] Tue, 7 Mar 2023 19:00:09 UTC (1,493 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻