The Polana–Eulalia Complex with JWST NIRSpec: Connections to Bennu, Ryugu, and Outer Solar System Bodies

Abstract Carbon-rich (C-complex) asteroids provide insight into the early solar system, and families of C-complex asteroids serve as robust samples for learning about the internal structure of planetesimals and the materials of the protoplanetary disk. This work investigates the compositions of asteroids within the Polana–Eulalia Complex (PEC) through analyses of JWST NIRSpec spectra , obtained as part of the Spectral Analysis of Main Belt Asteroids in the 3 μ m Region project. NIRSpec observations were conducted for the namesake asteroid of the Eulalia family, (495) Eulalia, as well as three members from the Polana family: (2441) Hibbs, (6712) Hornstein, and (6769) Brokoff. Analyses of the 2.7 μ m region demonstrate that PEC asteroids exhibit absorptions associated with Mg-rich phyllosilicates, in turn underscoring high—though incomplete—degrees of aqueous alteration in the past for both PEC families. Although consistent in regard to composition, (142) Polana and (495) Eulalia show deeper 2.7 μ m bands than the Polana family asteroids, suggesting slight differences in the degrees of aqueous alteration between large and small PEC asteroids. Minor absorptions from 3.0 to 4.0 μ m indicate that (495) Eulalia’s surface may contain more carbonates than (142) Polana, which potentially highlights slight differences between each family’s formation and evolution. Additionally, PEC asteroids also show spectral consistency with Bennu and Ryugu, reinforcing their shared origin in the PEC. Minor absorptions in PEC asteroid spectra also connect to small bodies within and beyond the main belt, providing further evidence of outer solar system formation for the PEC parent bodies.