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Carbonaceous asteroids allow us to study the original materials that formed the planets in the protoplanetary disk. They contain organic matter and (sub-)micrometer-size dust grains, called presolar grains, that condensed in the circumstellar envelopes of evolved stars and the ejecta of stellar explosions, such as novae and supernovae, before the formation of our Solar System. The isotopically anomalous organics are thought to have formed in the interstellar medium and the early Solar System. Whereas presolar grains provide insight into the building blocks of our Solar System, studying organics can help us understand the origin of life on Earth. These organics might have contributed to ingredients that helped life emerge. The return of samples from asteroid 101955 Bennu by NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission gives us a new opportunity to elucidate the formation mechanism(s) and evolution of organics, as well as the abundance and distribution presolar grains in carbonaceous asteroids. Here, we report on our ongoing work to characterize the isotopic and chemical compositions, microstructure, distribution, and abundance of insoluble organic matter (IOM) and presolar grains in Bennu samples. This work supports hypotheses 2 and 3 of the OSIRIS-REx Sample Analysis Plan.

On September 24, 2023, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission returned >70 g of material from asteroid Bennu to Earth. The Sample Return Capsule was opened at NASA Johnson Space Center (JSC), and a spillover sample was collected from the avionics deck to perform quick-look (QL) analyses. In addition to providing a reconnaissance investigation of its mineralogy, the sample was also examined for evidence of surface exposure on asteroid Bennu by identifying signatures of space weathering. Space weathering changes the morphology, microstructure, and chemistry of regolith on the surfaces of airless bodies. Driven by micrometeoroid bombardment and solar wind irradiation, our understanding of how space weathering modifies particles on the surfaces of carbonaceous asteroids is still developing. To bolster the interpretation of remote sensing data and to further address driving Hypothesis 10, we must investigate the nanoscale structural and chemical changes in returned samples from Bennu to understand how space weathering affects carbonaceous surface materials. Here we explore evidence for solar wind irradiation in QL samples from asteroid Bennu.

Asteroid (101955) Bennu is a B-type asteroid and a prime candidate for investigating the remnants of planet formation and enhancing our understanding of potential sources of crucial bio-essential elements for the early Earth. Remote observations of the surface of Bennu unveiled a terrain of boulders primarily composed of hydrated phyllosilicates, organic molecules, and carbonates. The hydrated nature of Bennu, the abundance of carbonates, and the presence of cm-scale carbonate veins provide clues to the nature of the building blocks of Bennu’s parent body and to its complex geological history. Here we present the first mineralogical, chemical, and isotopic results of analysis of phosphates in samples returned from Bennu by NASA’s OSIRIS-REx mission. We seek to test the hypothesis that heating of Bennu’s parent asteroid resulted in hydrothermal alteration in which melted ice reacted with the initial constituents.

The OSIRIS-REx spacecraft returned regolith samples from asteroid Bennu and an initial sample was allocated for quick-look (QL) analyses. These QL particles were recovered from the avionics deck of the sample canister and were used to test the hypothesis that this dust is broadly representative of the bulk sample. The QL sample analyses showed that the materials are dominated by hydrated silicates, sulfides, magnetite, phosphates, and abundant organic matter, in addition to other minor/trace phases. Here we report our preliminary transmission electron microscope (TEM) observations for the nanoscale mineralogy of Bennu samples.