Spectroscopic Investigation of Insoluble Organic Matter in Aubrites and Enstatite Chondrites

Abstract Raman spectroscopic investigation of chemically separated insoluble organic matter (IOM) from six aubrites and five enstatite chondrites revealed a bimodal range of temperatures spanning from ∼200 to ∼1,000°C points toward heterogeneously altered organics. Temperatures derived from graphitized or partially graphitized IOM from aubrites are similar to those reported earlier by mineral thermometry (∼900–1,000°C) and their presence in our samples, despite peak temperatures falling significantly below the temperature threshold for graphitization, suggests the involvement of metal‐catalyzed graphitization processes. The absence of an exciton peak in X‐ray absorption near edge structure spectra and the temperatures inferred from Raman spectroscopy suggest short‐term heating of IOM, potentially linked to impact‐related heating within the aubrite parent body (AuPB). The diverse temperature obtained for the aubrites in this study possibly indicates that the source of these organics could either be indigenous, that is, preserved during partial melting (incomplete differentiation of AuPB) or exogenous, that is, delivered through impact. High‐resolution transmission electron microscopy analysis reveals diverse IOM structures ranging from amorphous carbon to highly graphitic lamellar carbon phases and nanoglobules. Notably, the identification of nanoglobules, a feature typically associated with primitive chondrites, within one aubrite sample suggests the incorporation of exogenous organic material, possibly derived from primitive chondritic impactors.