Interstellar Polycyclic Aromatic Hydrocarbons and Carbon in Interplanetary Dust Particles and Meteorites

Abstract

Both interplanetary dust particles (IDP_s) and meteorites may contain material that is similar to polycyclic aromatic hydrocarbons(PAH_s). The Raman spectra of IDP_s and meteorites show features that are similar in position and relative strength to interstellar infrared emission features that have been attributed to vibrational transitions in free, molecular-sized PAH_s. The Raman spectra of some IDP_s also show red photoluminescence that is similar to the excess red emission seen in some astronomical objects and that has also been attributed to PAH_s and hydrogenated amorphous carbon. Moreover, a part of the carbonaceous phase in IDP_s and meteorites contains deuterium to hydrogen ratios that are greater than those for terrestrial samples. Deuterium enrichment is expected in small free PAH_s that are exposed to ultraviolet radiation in the interstellar medium. Taken together, these observations suggest that some of the carbonaceous material in IDP_s and meteorites may have been produced in circumstellar dust shells and only slightly modified in interstellar space.