A non-Vestan, eucrite-like pyroxene grain from asteroid (101955) BennuOPEN ACCESS
Zoë E. Wilbur, Timothy J. McCoy, Catherine M. Corrigan, Kazuhide Nagashima, Gary R. Huss, L. Robert Wardell, Timothy Gooding, Timothy R. Rose, Victoria E. Hamilton, Jessica J. Barnes, Kevin J. Walsh, Sara S. Russell, Daniella N. DellaGiustina, Harold C. Connolly Jr, Dante S. Lauretta
Earth and Planetary Science Letters, Available online 7 September 2026
“Highlights
- Exsolved pyroxene found in a Bennu sample indicates a basaltic source.
- Pyroxene texture and composition are similar to those of cumulate eucrites.
- Oxygen isotopes suggest the grain originated from a non-Vestan asteroid.
- Findings provide grain-scale evidence of planetary mixing on asteroid Bennu.
- Bennu serves as an archive for previously unsampled asteroids.”
“Exogenous fragments in brecciated planetary materials offer direct evidence of mixing among planetary bodies in the Solar System. Fragments of undifferentiated carbonaceous material are frequently identified in differentiated meteorites. However, differentiated fragments are rarely observed in carbonaceous material. An exception is the exogenous basalt observed by the OSIRIS-REx spacecraft on the carbonaceous asteroid (101955) Bennu, which motivated a search for differentiated material in the returned samples. We report a pyroxene grain in a brecciated Bennu sample that is texturally and compositionally like pyroxene from cumulate eucrites — basaltic meteorites linked to the differentiated asteroid (4) Vesta — but oxygen isotopic measurements indicate that it is likely sourced from a basaltic asteroid not clearly represented among known basaltic achondrites. This grain may have been delivered to a precursor to Bennu in the main asteroid belt. Whether this grain is representative of the pyroxene-rich boulders observed remotely on Bennu’s surface remains unconstrained. Nevertheless, extending spacecraft observations to the grain scale reveals that Bennu serves as an archive for uncharacterized basaltic asteroids, documenting a history of planetary mixing that is otherwise elusive in current meteorite records.”
