S. Messenger, S. J. Clemett, S. Amari, X. Gao, R. M. Walker, X. D. F. Chillier, and R. N. Zare, “Indigenous Polycyclic Aromatic Hydrocarbons in Circumstellar Graphite Grains from Primitive Meteorites,” Astrophysical Journal 502, 284-295 (1998).