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; D. S. Lauretta

AI summary · arXiv: 2610.31828v1 · astro-ph.EP

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,

and 15 more authors

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, D. S. Lauretta

Original paper Submitted to arXiv on 22 Oct. 2026 76 pages including Supplemental Information License: CC BY-NC-ND 4.0

How to read this summary? Illustrated guide

The essentials

Measurements of 63 elements in Bennu aggregate samples show strong compositional homogeneity and close agreement with CI chondrites for non-highly volatile elements.

Based on the abstract only: check the details in the original paper.

Question

How does the bulk elemental composition of returned Bennu material compare with CI chondrites and solar photospheric abundances? Is Bennu material compositionally consistent across aggregate samples and sample masses?

Method

The authors measured concentrations of 63 elements in aggregate Bennu material representing a combined mass of approximately 8 g, analyzing samples across four laboratories. They compared homogenized and non-homogenized samples, subsamples, and sample masses from tens of milligrams to several grams, then combined the results into an average composition termed Best Bulk Bennu (B3).

Findings

Result The analyses found no statistically significant compositional differences among aliquots of two homogenized aggregate samples or among subsamples of a non-homogenized aggregate sample.
See the passage in the paper
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.
Result The authors detected no measurable elemental-composition variation across sample masses from tens of milligrams to several grams.
See the passage in the paper
Nor do we find measurable variations among sample masses ranging from tens of milligrams to several grams.
Authors’ interpretation The findings indicate that returned Bennu material is well mixed at the aggregate scale.
See the passage in the paper
These findings indicate that the material returned from Bennu is well mixed at the aggregate scale.
Authors’ interpretation B3 agrees with the average CI chondrite composition within analytical uncertainties, supporting the conclusion that terrestrial alteration of CI chondrites is effectively isochemical for non-highly volatile elements.
See the passage in the paper
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.
Authors’ interpretation B3 and the CI chondrite average compare similarly with solar photospheric composition, and the authors identify both as the best available materials for estimating bulk Solar System composition for non-highly volatile elements.
See the passage in the paper
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.

Limitations

The study's reported compositional comparison and recommendation concern non-highly volatile elements, so they do not establish the same conclusions for highly volatile elements.
See the passage in the paper
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.

Why it matters

The authors argue that returned Bennu material provides a well-mixed reference composition that can refine estimates of bulk Solar System abundances. Its agreement with CI chondrites supports using CI meteorites and carbonaceous asteroid samples to estimate non-highly volatile elemental composition.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: Bennu CI chondrites bulk elemental composition OSIRIS-REx Solar System abundances

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Comprehensive Summary
Layman's Summary
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Original abstract

The paper investigates whether asteroid Bennu’s bulk elemental composition can provide a reliable estimate of the early Solar System’s composition and how it compares with Ivuna-type (CI) carbonaceous chondrites. CI chondrites have often served as proxies for bulk Solar System composition because the abundances of many elements in them resemble those measured in the Sun’s photosphere. However, terrestrial alteration may have changed their minerals and redistributed water-mobile elements. Samples returned by NASA’s OSIRIS-REx mission offer a way to test this comparison using material that has not undergone the same terrestrial history. The authors measured 63 elements in unsorted Bennu aggregate material. Four laboratories analyzed samples with a combined mass of about 8 grams. The study compared aliquots from two aggregate samples homogenized into powders with subsamples from a non-homogenized aggregate, including two previously reported subsamples. It also assessed whether sample mass, ranging from tens of milligrams to several grams, affected the measured composition. The abstract does not specify the analytical techniques, individual element concentrations, or measurement uncertainties. The authors found no statistically significant compositional differences among the aliquots and subsamples within analytical uncertainties. They also detected no measurable variation associated with sample mass across the tested range. These results indicate that the analyzed material is well mixed at the aggregate scale: within the analyses’ resolution and precision, small and large subsamples yield consistent bulk compositions. The authors combined the measurements to derive an average bulk elemental composition, which they named Best Bulk Bennu (B3). B3 agrees closely with the average CI chondrite composition within analytical uncertainties. They conclude that terrestrial alteration has not significantly changed CI chondrites’ bulk abundances of non-highly volatile elements, even if it has affected their minerals or redistributed more mobile elements. B3 and the CI average also compare similarly with solar photospheric composition. The authors therefore identify CI meteorites and returned carbonaceous-asteroid samples as the best available materials for estimating bulk Solar System abundances of non-highly volatile elements. These findings support the use of CI chondrites for this purpose while providing an independent comparison with asteroid material. They also suggest that Bennu’s aggregate-scale composition is sufficiently uniform for a combined bulk estimate to be meaningful. However, the conclusions are limited to what the abstract reports. Because the full text is unavailable, detailed procedures, element-by-element results, numerical uncertainties, and qualifications on the comparison cannot be assessed. The reported agreement applies within analytical uncertainties and to non-highly volatile elements; the abstract does not establish equivalent conclusions for highly volatile elements or for every scale of variation within Bennu.

What Bennu Can Tell Us About the Solar System’s Ingredients

How can scientists estimate the original ingredients of the Solar System? One useful clue has long come from CI carbonaceous chondrites, a rare type of meteorite whose abundances of many elements resemble those measured in the Sun’s outer atmosphere. But these rocks have spent time on Earth, where water and other environmental processes may have altered their minerals or moved some elements around.

A study titled “Best Bulk Bennu (B3): Elemental compositions of aggregate samples from asteroid Bennu,” by K. Wang, K. Lodders, P. Koefoed, M. Broussard, J. Wimpenny, J. Render et al., puts that comparison to the test with material returned from asteroid Bennu by NASA’s OSIRIS-REx mission. The central question: does Bennu’s elemental makeup support using CI meteorites as a guide to the Solar System’s bulk composition?

A Close Look at Bennu’s Bulk Composition

The researchers measured 63 elements in unsorted Bennu aggregate material. Four laboratories analyzed samples with a combined mass of about 8 grams. The study included aliquots from two aggregates that had been homogenized into powders, as well as subsamples from a non-homogenized aggregate. Two of those subsamples had been reported previously.

The researchers also examined whether the amount of material analyzed made a difference. Sample masses ranged from tens of milligrams to several grams—a practical consideration when comparing small pieces of returned asteroid material with larger samples.

Did the samples agree?

Within analytical uncertainties, the measurements showed no statistically significant compositional differences among the aliquots and subsamples. Nor did the researchers detect a measurable change in composition associated with sample mass across the tested range.

That consistency suggests the analyzed material is well mixed at the aggregate scale, at least within the resolution and precision of the analyses. In other words, the small and large subsamples produced consistent estimates of bulk composition. It does not demonstrate that every part of Bennu is identical, but it supports combining these measurements into a meaningful average for the material studied.

Introducing Best Bulk Bennu

Combining the measurements, the authors derived an average composition they named Best Bulk Bennu, or B3. They found that B3 agrees closely with average CI chondrite composition within analytical uncertainties.

This result matters because CI meteorites have a complicated history. Their minerals may have changed through terrestrial alteration, and water-mobile elements may have been redistributed. Yet the comparison with Bennu indicates that such alteration has not significantly changed CI chondrites’ bulk abundances of non-highly volatile elements.

B3 and the CI average also compare similarly with the Sun’s photospheric composition. Together, these findings support using both CI meteorites and returned carbonaceous-asteroid samples as the best available materials for estimating bulk Solar System abundances of non-highly volatile elements.

What the Findings Do—and Don’t—Show

The study offers an independent check on a long-used reference. Bennu’s agreement with CI chondrites strengthens the case that CI compositions remain useful for estimating the Solar System’s non-highly volatile elemental inventory, even though the meteorites have experienced changes on Earth. It also suggests that combining Bennu measurements can provide a reliable bulk estimate for the aggregate material analyzed.

There are important limits to the conclusions. The reported agreement applies within analytical uncertainties and specifically to non-highly volatile elements. It should not be extended automatically to highly volatile elements, or taken as proof that all locations or scales within Bennu have the same composition.

The summary of the paper also does not provide the analytical techniques, individual element concentrations, numerical uncertainties, or detailed qualifications behind the comparison. Those details would be needed to assess how strongly each element supports the overall result.

A Useful Bridge Between Meteorites and Asteroids

Bennu’s returned material gives researchers a chance to compare asteroid matter with meteorites that have been shaped by Earth’s environment. In this study, the samples’ consistent measurements and close agreement with CI chondrites point to a shared picture of the Solar System’s bulk composition—at least for the non-highly volatile elements examined.

The result does not make CI meteorites a perfect record of every element or every stage of Solar System history. Instead, it adds confidence to a specific and valuable use: treating CI chondrites, alongside returned carbonaceous-asteroid samples such as Bennu’s, as strong references for the bulk abundances of many elements.

Created on 30 Oct. 2026

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

The essentials

Question

Method

Findings

Limitations

Why it matters

Read further

Definitions

What Bennu Can Tell Us About the Solar System’s Ingredients

A Close Look at Bennu’s Bulk Composition

Did the samples agree?

Introducing Best Bulk Bennu

What the Findings Do—and Don’t—Show

A Useful Bridge Between Meteorites and Asteroids

Ask questions about this paper to our AI assistant

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