¹E.A. Cloutis et al. (>10)
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117289]
¹Centre for Terrestrial and Planetary Exploration (C-TAPE), University of Winnipeg, 515 Portage Avenue, Winnipeg R3B 2E9, Manitoba, Canada
Copyright Elsevier

We measured reflectance spectra (250–2500 nm) of a 200 mg aliquot (sample id OREX-800029-0) of aggregate (unsorted) regolith particles returned from asteroid Bennu by the OSIRIS-REx mission). Our measurements include spots centered on small (<0.5 mm), medium (0.5–1 mm), and large particles (1–2 mm), as well as spots dominated by larger individual particles, including angular, hummocky, and mottled examples. The ultraviolet (UV) spectra (250–450 nm) are characterized by low reflectance (<3%), slightly red spectral slopes, absorption features near 270 and 320 nm attributable to Fe²⁺-O charge transfers, and Fe³⁺-associated absorption features, respectively. The 450–2500 nm region spectra are of low reflectance (<3% at 550 nm), red-sloped, and exhibit variable but weak absorption features, the most ubiquitous being a broad region of absorption in the 1000 nm region (<~2%), attributable to magnetite and Fe²⁺-bearing phyllosilicates. The low albedo, weak absorption features, and red-sloped spectra can be attributed to the presence of carbonaceous components. Overall, we confirm the spectral similarities between Bennu aggregate material and powders of the rare CI1 chondrite meteorites. The spectra we measured are generally red-sloped, in contrast to the blue-sloped global-average spectra measured by ground-based telescopes and the OSIRIS-REx spacecraft. This difference is consistent with Bennu’s boulder-dominated surface and limited fine-grained dust, in combination with compositional contributions from optically efficient minor phases.

¹Poula Eyðbjørnsdóttir, ¹Anders Johansen, ¹Elishevah van Kooten
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [DOI: 10.1016/j.gca.2026.07.028]
¹Center for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark.
Copyright Elsevier

Chondrules and their associated fine-grained rims (FGRs) record fundamental processes operating in the early protoplanetary disk, yet the relationship between chondrule chemistry, morphology, and matrix complementarity remains incompletely understood. Here we investigate the major, minor, and trace element compositions of 66 chondrules and associated FGRs from relatively unaltered CM carbonaceous chondrites Asuka 12236, Paris and Maribo in relation to their three-dimensional morphology, using a multi-analytical approach including femtosecond LA-ICP-MS and X-ray tomography. Our results show that CM chondrules record a systematic process of metal loss and evaporation of Si-rich mesostasis, driving initially CI-like precursor compositions toward more Mg- and Si-rich bulk compositions along the CI ratio line and toward increasingly Si-poor forsteritic mineral assemblages. GEMS-like materials in pristine CM matrices appear to mirror chondrule compositions and likely represent complementary condensates derived from evaporated Si-rich mesostasis. The dust accreted to chondrules is dominantly CI-like but incorporates ∼ 14 wt% complementary condensate material represented by chondritic amorphous silicates, reconciling the observed Mg/Si complementarity between chondrules and matrix with the preservation of primordial organics and presolar grains.

Morphological observations further reveal no significant sectioning bias in chondrule size or plane, consistent with CM chondrule populations being dominated by agglomerates of ∼ 100 μm sized microspherules rather than larger primary melt droplets. Many chondrules display grape-bunch textures formed by welding of smaller primary chondrules with metal-rich or CI-like rims. This structure may explain the moderate volatile element plateau at ∼ 0.3 × CI observed for average CM chondrule compositions, reflecting incorporation of primary fine-grained rim material into these aggregates. We propose a “micro-chondrule-first” formation scenario in which localized heating events produced small molten droplets that subsequently accreted CI-like dust and ice, aggregated, and experienced limited in situ aqueous alteration. These observations place new constraints on chondrule formation mechanisms in the outer disk and highlight the importance of localized melting and aggregation processes.