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

@misc{wang2026best,
  title = {{Best Bulk Bennu (B3): Elemental compositions of aggregate samples from asteroid Bennu}},
  author = {K. Wang and K. Lodders and P. Koefoed and M. Broussard and J. Wimpenny and J. Render and Q. R. Shollenberger and T. S. Kruijer and G. A. Brennecka and M. Amini and V. Lai and D. Weis and K. C. Welten and K. Nishiizumi and D. P. Glavin and J. P. Dworkin and C. M. O'D. Alexander and J. -A. Barrat and P. Haenecour and J. J. Barnes and A. N. Nguyen and H. C. Connolly Jr. and D. S. Lauretta},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.31828},
  eprint = {2610.31828},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.31828},
  note = {CC BY-NC-ND 4.0},
}

TY  - UNPB
TI  - Best Bulk Bennu (B3): Elemental compositions of aggregate samples from asteroid Bennu
AU  - K. Wang
AU  - K. Lodders
AU  - P. Koefoed
AU  - M. Broussard
AU  - J. Wimpenny
AU  - J. Render
AU  - Q. R. Shollenberger
AU  - T. S. Kruijer
AU  - G. A. Brennecka
AU  - M. Amini
AU  - V. Lai
AU  - D. Weis
AU  - K. C. Welten
AU  - K. Nishiizumi
AU  - D. P. Glavin
AU  - J. P. Dworkin
AU  - C. M. O'D. Alexander
AU  - J. -A. Barrat
AU  - P. Haenecour
AU  - J. J. Barnes
AU  - A. N. Nguyen
AU  - H. C. Connolly Jr.
AU  - D. S. Lauretta
PY  - 2026
DA  - 2026/10/22
PB  - arXiv
DO  - 10.48550/arxiv.2610.31828
UR  - https://arxiv.org/abs/2610.31828
AB  - 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.
ER  -