240-3 Aromatic Hydrocarbons, Nanoglobules and Macromolecular Organic Matter in Returned Samples from Asteroid 101955 Bennu

Session: From Atoms to Asteroids and Habitable Planets: Coordinated Analysis of Planetary Samples and Their Terrestrial Analogues

Presenting Author:

Simon Clemett

Authors:

Clemett, Simon John¹, Thomas-Keprta, Kathie Louise², Nguyen, Lan-anh³, Keller, Lindsay⁴, Le, Loan⁵, Rahman, Zia⁶, Harrington, Roger⁷, Glavin, Daniel⁸, Jason, Dworkin⁹, Connolly, Harold¹⁰, Lauretta, Dante¹¹

(1) Asterion / Amentum, NASA Johnson Space Center, Houston, Texas, USA, (2) Barrios / Amentum, NASA Johnson Space Center, Houston, Texas, USA, (3) ARES, NASA Johnson Space Center, Houston, Texas, USA, (4) ARES, NASA Johnson Space Center, Houston, Texas, USA, (5) Amentum, NASA Johnson Space Center, Houston, Texas, USA, (6) Amentum, NASA Johnson Space Center, Houston, Texas, USA, (7) Amentum, NASA Johnson Space Center, Houston, Texas, USA, (8) Planetary Studies, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA, (9) Solar System Analysis, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA, (10) Rowan University, Glassboro, New Jersey, USA; Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA, (11) Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA,

Abstract:

The return of samples from the asteroid Bennu by NASA’s OSIRIS-REx (OREX) mission provides a unique opportunity to study pristine asteroid material not represented in current meteorite collections. We report here the identification of curious, isotopically anomalous, aromatic sub-mm sized microstructures within Bennu samples that are intimately associated with organic nanoglobules.

The analysis of aromatic organic matter in subsamples of two Bennu stones OREX-800055 & OREX-800088, representative of “angular” and “hummocky” lithologies, were performed by the complementary techniques of microprobe two-step laser mass spectrometry (μL²MS) and UV fluorescence. Free polycyclic aromatic hydrocarbons (PAHs) being mapped by μL²MS and macromolecular aromatic phases being identified by UV fluorescence.

PAHs were observed distributed through the Bennu matrix with a spatial granularity on the order of ~100 μm and ranged in size from 1- to 5-rings with extended alkylation series. This is similar to PAHs previously observed in the more aqueously altered carbonaceous meteorites. Notably the PAH abundance varied with sample lithology, being higher in the angular vs. hummocky lithology. UV fluorescence imaging of the same regions revealed the matrix was interspersed discrete μm to sub-μm hotspots that were identified as organic nanoglobules. Kernel density estimations of the distribution of nanoglobules showed a casual association with the spatial distribution of PAHs observed by μL²MS.

When applied to larger area petrographic sections UV fluorescence revealed, in addition to nanoglobules, significantly larger (10 - 50 μm) hot-spots corresponding to discrete carbonaceous features that optically appeared as subtle red-brown discolorations in the phyllosilicate matrix. Subsequent isotopic analysis by nanoSIMS revealed substantial δ¹²C and δ¹⁵C anomalies indicating the carbonaceous features formed prior to their accretion onto Bennu or its progenitor. Their intrinsic fluorescence is consistent with aromatic moieties with the same conjugation size as the free PAHs observed by μL²MS. Transmission electron microscopy imaging of ion bean extracted thin sections showed a range of textures from a smooth contiguous organic matrix with embedded sub-μm clusters of anhydrous amorphous silicates and sulphides through to massive nanoglobule aggregates tightly intertwined with phyllosilicate veins. This is interpreted as an aqueous alteration sequence with an initial uniform organic matrix undergoing progressive deagglomeration along with concomitant phyllosilicate incursion resulting in nanoglobule / phyllosilicate assemblages and eventually dissemination of nanoglobules into the surrounding mineral matrix.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8789

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