The origin of the 3.4 micron feature in Wild 2 cometary particles and in ultracarbonaceous interplanetary dust particles

TL;DR

This study uses infrared spectroscopy to analyze interplanetary dust particles and cometary samples, revealing that their organic materials likely originate from the outer solar nebula rather than interstellar space.

Contribution

It provides new insights into the origin of organic compounds in cometary and interplanetary dust particles, challenging the previous interstellar origin hypothesis.

Findings

3.4 micron band dominated by CH2 groups in samples

Presence of carbonyl groups indicates oxygen bonding

Samples' spectral features differ from interstellar medium

Abstract

We analyzed 2 ultra-carbonaceous interplanetary dust particles and 2 cometary Wild 2 particles with infrared spectroscopy. We characterized the carrier of the 3.4 micron band in these samples and compared its profile and the CH2/CH3 ratios to the 3.4 micron band in the diffuse interstellar medium (DISM), in the insoluble organic matter (IOM) from 3 primitive meteorites, in asteroid 24 Themis and in the coma of comet 103P/Hartley 2. We found that the 3.4 micron band in both Wild 2 and IDPs is similar, but different from all the other astrophysical environments that we compared to. The 3.4 micron band in 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-1 (5.8 micron) 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 these observations we conclude that the origin of the carrier of the 3.4 micron band in IDPs and Wild 2 samples is not interstellar, instead, we suggest that the origin lies in the outermost parts of the solar nebula.