Abstract
Context. Because comets are part of the most primitive bodies of our solar system, establishing their chemical composition and comparing them to other astrophysical bodies gives new constraints on the formation and evolution of organic matter throughout the solar system. For two years, the time-of-flight secondary ion mass spectrometer COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta orbiter performed in situ analyses of the dust particles ejected from comet 67P/Churyumov-Gerasimenko (67P). Aims. The aim is to determine the H/C elemental ratio of the refractory organic component contained in cometary particles of 67P. Methods. We analyzed terrestrial and extraterrestrial calibration samples using the COSIMA ground-reference model. Exploiting these calibration samples, we provide calibration lines in both positive and negative ion registration modes. Thus, we are now able to measure the cometary H/C elemental ratio. Results. The mean H/C value is 1.04 ± 0.16 based on 33 different cometary particles. Consequently, the H/C atomic ratio is on average higher in cometary particles of 67P than in even the most primitive insoluble organic matter extracted from meteorites. Conclusions. These results imply that the refractory organic matter detected in dust particles of 67P is less unsaturated than the material in meteorites.
Highlights
Comets are small bodies that are thought to have formed in the early protoplanetary disk
We only considered the analysis performed on the noncontaminated areas of the insoluble organic matter (IOM) samples in order to obtain representative mass spectanrneadg. aEStviiv2eOenm(bCyoHdd3eo))i+5nagirnesposot,isfllirtaoigvbemsemernvotedideonainsndtohfCePHfiD3nMSailOSse−(mleacnatidinoClnyH,Sa3ilS(tChiOoHu−23g)inh+3 their intensities are much lower than the values in the spectra acquired on the gold target
The COmetary Secondary Ion Mass Analyzer (COSIMA) mass spectrometer collected, imaged, and analyzed in situ the dust particles ejected from comet 67P/Churyumov-Gerasimenko
Summary
Comets are small bodies that are thought to have formed in the early protoplanetary disk. They are believed to contain unmodified materials since their formation (Willacy et al 2015). The cometary organic matter was difficult to characterize because of the high-velocity impacts (about 70 km s−1) of the particles, releasing mostly mono-atomic ions rather than polyatomic ions (Kissel & Krueger 1987). The average elemental composition for the dust determined by Jessberger et al (1988) shows that the carbon-to-magnesium ratio was about ten times higher in the particles of 1P/Halley than in CI carbonaceous chondrites, demonstrating that comets are among the most carbon-rich bodies of the solar system
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