The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley1,2. Such matter is generally thought to have originated in the interstellar medium3, but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed4. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization5. Many gaseous organic molecules, however, have been observed6,7,8,9; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei8. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula10. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites11,12. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies11. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.
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COSIMA was built by a consortium led by the Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany, in collaboration with: the Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, Orléans, France; the Institut d’Astrophysique Spatiale, CNRS/Université Paris Sud, Orsay, France; the Finnish Meteorological Institute, Helsinki, Finland; the Universität Wuppertal, Wuppertal, Germany; von Hoerner und Sulger GmbH, Schwetzingen, Germany; the Universität der Bundeswehr, Neubiberg, Germany; the Institut für Physik, Forschungszentrum Seibersdorf, Seibersdorf, Austria; and the Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften, Graz, Austria; and is led by the Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany. We acknowledge the support of the national funding agencies of Germany (Deutsches Zentrum für Luft- und Raumfahrt (DLR), grant 50 QP 1302), France (Centre National d’Étude Spatiales (CNES)), Austria, Finland and the European Space Agency (ESA) Technical Directorate. A.B. acknowledges support from the CNES and the Labex Exploration Spatiale des Environnements Planétaires (ESEP; no. 2011-LABX-030), and funding from the Idex Paris Sciences et Lettres (PSL; no. ANR-10-IDEX-0001-02). S.S. acknowledges support from the Swedish National Space Board grant (contracts 121/11 and 198/15). H.L., B.Z. and K.L. acknowledge Academy of Finland grant 277375. We thank the Rosetta Science Ground Segment at the European Space Astronomy Centre, the Rosetta Mission Operations Centre at the European Space Operations Centre, and the Rosetta Project at the European Space Research and Technology Centre for their work, which enabled the scientific return of the Rosetta mission.
The authors declare no competing financial interests.
Nature thanks C. Alexander and the other anonymous reviewer(s) for their contribution to the peer review of this work.
After the proprietary period of six months, the data will be available in the ESA Planetary Science Archive (see Methods).
Extended data figures and tables
These sub-pixel sampled images have an equivalent resolution of 10 μm (ref. 15). Each is the sum of two images, obtained with two grazing incidence illuminations from the left and the right. A square-root scaling has been used to bring out weakly illuminated regions. These images were acquired on 4 June 2015 (Kenneth) and 25 November 2015 (Juliette).
The spectra in red were acquired on the cometary particles named Fadil, Jean-Pierre, Jessica, Kerttu and Stefane. The spectra in black were acquired on the respective gold targets, near the cometary particles. The latter spectra are normalized to the intensity of characteristic fragments of PDMS observed on the particles (see Methods). a, Positive-ion spectra. b, c, Enlargements from a. d, Negative-ion spectra. More details about the particles are in Extended Data Table 1.
The spectra in red were measured on the two cometary particles studied here, Kenneth and Juliette, and on an IOM sample extracted from the Orgueil and Murchison chondrites. The spectra in black were measured on the targets, near the cometary particles or the IOM samples.
Extended Data Figure 4 Spatial distribution of the carbon secondary ions of the particles Kenneth and Juliette.
The colour scale shows the values of the carbon/PDMS intensity ratios, on and off the particles, in negative and positive modes. The white ellipses indicate the size of the footprint of the primary ion beam, 35 × 50 μm2 (full-width at half-maximum). These spatial distributions have been superimposed on the optical images of the particles.
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Fray, N., Bardyn, A., Cottin, H. et al. High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko. Nature 538, 72–74 (2016). https://doi.org/10.1038/nature19320
Chemical and Isotope Composition of Comet 67P/Churyumov−Gerasimenko: The Rosetta−Philae Mission Results Reviewed in the Context of Cosmogony and Cosmochemistry
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