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Published online by Cambridge University Press: 06 October 2025
A family of unidentified infrared emission (UIE) bands is widely observed in planetary nebulae. We suggest that the carriers of the UIE bands are mixed aromatic/aliphatic organic nanoparticles (MAONs) synthesized over thousand-year time scales in the nebulae. The possible chemical pathways of synthesis is discussed. These organics are ejected into the interstellar medium and could have enriched the primordial Solar System, leading to the reservoir of complex organics in comets, asteroids, planetary satellites, and interplanetary dust particles.