Carbonaceous Cosmic Dust Analogs Distinguish between Ion Bombardment and Temperature

Abstract Carbonaceous cosmic dust is formed in the circumstellar envelopes of asymptotic giant branch stars and supernovae ejecta. Reprocessed carbonaceous cosmic dust, abundant in the light elements C, H, O, and N is found in asteroids and comets. These elements form dust that is well described as an amorphous, covalently bonded network solid with a structure that is expected to reflect the key formative influences of ion bombardment, temperature modification, and UV irradiation. Ion bombardment of a dust grain by an energetic particle in a stellar wind creates a nonequilibrium thermal spike event, which contrasts with the close-to-equilibrium process of annealing under the local ambient conditions. There is a gap in our knowledge of how to distinguish ion bombardment as a synthesis process from postsynthesis thermal modification through infrared spectroscopy. Here we synthesize dust from molecular precursors under a range of controlled space-like conditions to form a database of IR spectra. We apply principal component analysis to show that the first principal component correlates with ion bombardment intensity during synthesis and the second principal component correlates with annealing temperature. The spectral loading curves of these two principal components are proposed as potential diagnostic tools to uncover past formative influences on cosmic dust as well as on the carbonaceous content of asteroids such as Bennu and Ryugu. Amorphous organic networks composed of the CHON elements unify previous ideas on cosmic dust by encompassing features of PAHs, tholins, and mixed aliphatic–aromatic nanoparticles.