Best Bulk Bennu (B3): Elemental compositions of aggregate samples from asteroid Bennu

K. Wang; K. Lodders; P. Koefoed; M. Broussard; J. Wimpenny; J. Render; Q. R. Shollenberger; T. S. Kruijer; G. A. Brennecka; M. Amini; V. Lai; D. Weis; K. C. Welten; K. Nishiizumi; D. P. Glavin; J. P. Dworkin; C. M. O'D. Alexander; J. -A. Barrat; P. Haenecour; J. J. Barnes; A. N. Nguyen; H. C. Connolly Jr.; D. S. Lauretta

arXiv · 2610.31828

Best Bulk Bennu (B3): Elemental compositions of aggregate samples from asteroid Bennu

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Abstract

Ivuna-type (CI) carbonaceous chondrites have long served as proxies for the bulk Solar System composition due to their close agreement with solar photospheric abundances and enrichment in volatile elements relative to other chondrite classes. However, CI chondrites have been subject to terrestrial alteration, which may have modified their original mineralogies and redistributed aqueously mobile elements. NASA's OSIRIS-REx mission delivered pristine material from the carbonaceous asteroid Bennu, and initial analyses revealed close compositional similarities with CI chondrites. This provides a valuable opportunity to refine estimates of the bulk Solar System composition. We report concentrations of 63 elements in aggregate (bulk, unsorted) Bennu material (representing a combined mass of ~8 g) analyzed across four laboratories. Within analytical uncertainties, we find no statistically significant differences among aliquots of two aggregate samples that were homogenized into powders, or among subsamples (including two previously reported) of a non-homogenized aggregate sample. Nor do we find measurable variations among sample masses ranging from tens of milligrams to several grams. These findings indicate that the material returned from Bennu is well mixed at the aggregate scale. Combining all of the data, we derive an average bulk elemental composition that we term Best Bulk Bennu (B3). Comparison of B3 with an average CI chondrite composition shows excellent agreement within analytical uncertainties, confirming that terrestrial alteration of CI chondrites is effectively isochemical for non-highly volatile elements. B3 and the CI chondrite average composition compare similarly to solar photospheric composition. Thus, CI meteorites and returned samples of carbonaceous asteroids are the best available materials for estimating the bulk Solar System composition of non-highly volatile elements.

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K. Wang, K. Lodders, P. Koefoed, M. Broussard, J. Wimpenny, J. Render, Q. R. Shollenberger, T. S. Kruijer, G. A. Brennecka, M. Amini, V. Lai, D. Weis, K. C. Welten, K. Nishiizumi, D. P. Glavin, J. P. Dworkin, C. M. O'D. Alexander, J. -A. Barrat, P. Haenecour, J. J. Barnes, A. N. Nguyen, H. C. Connolly Jr., D. S. Lauretta. 2026-10-22. Best Bulk Bennu (B3): Elemental compositions of aggregate samples from asteroid Bennu. https://arxiv.org/abs/2610.31828

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