2013ApJ...765..145M

We analyzed two ultracarbonaceous interplanetary dust particles (IDPs) and two cometary Wild 2 particles with infrared spectroscopy. We characterized the carrier of the 3.4 µm band in these samples and compared its profile and the CH₂/CH₃ ratios to the 3.4 µm band in the diffuse interstellar medium (DISM), in the insoluble organic matter from three primitive meteorites, in asteroid 24 Themis, and in the coma of comet 103P/Hartley 2. We found that the 3.4 µm band in both Wild 2 and IDPs is similar, but different from all of the other astrophysical environments that we compared it to. The 3.4 µm band in the IDPs and Wild 2 particles is dominated by CH₂ groups, the peaks are narrower and stronger than in the meteorites, asteroid Themis, and the DISM. Also, the presence of the carbonyl group C=O at ∼1700/cm (5.8 µm) in most of the spectra of our samples indicates that these aliphatic chains have O bonded to them, which is quite different from astronomical spectra of the DISM. Based on all of these observations, we conclude that the origin of the carrier of the 3.4 µm band in the IDPs and Wild 2 samples is not interstellar; instead, we suggest that the origin lies in the outermost parts of the solar nebula.