154 Asteroid Observations, Return Missions, and Meteoritics: Interweaving Perspectives and Data (Posters)

The new age of sample return missions affords opportunities to intercalibrate observational and laboratory results. This session invites studies using observational tools, return mission data and materials, and meteorites to advance our knowledge of asteroids.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Presolar Grains in Hummocky and Angular Particles from Asteroid Bennu

Paper number: 154-7
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Presolar grains that formed in the outflows and explosions of evolved stars seeded the molecular cloud that formed our solar system. These grains are preserved in primitive asteroid and comet samples. The detailed isotopic, mineralogical, and chemical study of presolar grains provides information on the initial materials that contributed to the formation of the solar system and the planetary bodies within it. Here we characterized presolar grains present in samples of asteroid Bennu returned by NASA’s OSIRIS-REx mission to understand the nature and distribution of presolar materials that were accreted by the parent asteroid and to assess the degree of parent body hydrothermal alteration.

 

We analyzed intermediate-sized (~0.5–1 mm) Bennu particles of the angular (OREX-803165-0, OREX-803170-0) and hummocky (OREX-803172-0) lithologies that were embedded in epoxy and dry polished. Coordinated analysis of the particles entailed acquisition of images and elementals maps by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Isotope mapping was conducted using nanoscale secondary ion mass spectrometry (NanoSIMS) to identify isotopically anomalous grains. Electron transparent cross-sections of select presolar grains were produced by focused ion beam (FIB) methods and the mineralogy and chemical compositions were assessed by scanning transmission electron microscopy (STEM).

 

A total of 63 carbon-rich and 25 oxygen-rich presolar grains were identified. Presolar SiC grains are affected by heating in the nebula and on the parent boy. The abundance of these grains in Bennu (~45 ppm) are consistent with abundances in unheated chondritic meteorites, indicating that the parent asteroid did not experience high temperatures. However, the proportion of SiC grains from supernova is six times greater in the Bennu samples than in other asteroid materials. Bennu’s parent asteroid therefore accreted material from a region of the protoplanetary disk that was enriched in supernova SiC grains.

 

Presolar silicates are particularly susceptible to destruction by aqueous alteration. We find that the presolar silicate abundances in the Bennu particles generally support substantial aqueous alteration on the parent asteroid. However, three chemically distinct clasts in the hummocky Bennu particle contained higher abundances of presolar silicate grains (~90 vs. 4 ppm), denoting their less-altered nature. TEM analysis shows the presolar grains from these clasts retain their crystallinity and lack evidence for parent body alteration. Aqueous alteration was therefore heterogeneous on Bennu’s parent asteroid.

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

doi: 10.1130/abs/2025AM-413717

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.