Infrared detection of aliphatic organics on a cometary nucleus


The European Space Agency’s Rosetta mission1 has acquired unprecedented measurements of the surface of the nucleus of comet 67P/Churyumov–Gerasimenko (hereafter, 67P), the composition of which, as determined by in situ and remote-sensing instruments, including the VIRTIS instrument2, seems to be an assemblage of ices, minerals and organic material3. We performed a refined analysis of infrared observations of the nucleus of 67P carried out by the VIRTIS-M hyperspectral imager. We find that the overall shape of the infrared spectrum of 67P is similar to that of other carbon-rich outer Solar System objects, suggesting a possible genetic link with them. More importantly, we also confirm the complex spectral structure of the wide 2.8–3.6 µm absorption feature populated by fainter bands. Among these, we unambiguously identify the presence of aliphatic organics by their ubiquitous 3.38 µm, 3.42 µm and 3.47 µm bands. This infrared detection of aliphatic species on a cometary surface has strong implications for the evolutionary history of the primordial Solar System and is evidence that comets provide an evolutionary link between interstellar material and Solar System bodies4.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Average spectrum of 67P.
Fig. 2: Comparison of the aliphatic features on 67P and in the ISM and IOM, shown in arbitrary units, with offsets.
Fig. 3: Comparison between 67P spectrum and other bodies of the Solar System, normalized at 2.3 µm.

Data availability

All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Information. The VIRTIS calibrated data are available through the European Space Agency’s Planetary Science Archive (


  1. 1.

    Glassmeier, K. H., Boehnhardt, H., Koschny, D., Kührt, E. & Richter, I. The Rosetta mission: flying towards the origin of the Solar System. Space Sci. Rev. 128, 1–21 (2007).

  2. 2.

    Coradini, A. et al. VIRTIS: an imaging spectrometer for the Rosetta mission. Space Sci. Rev. 128, 529–559 (2007).

  3. 3.

    Filacchione, G. et al. Comet 67P/CG nucleus composition and comparison to other comets. Space Sci. Rev. 215, 19 (2019).

  4. 4.

    Mumma, M. J. & Charnley, S. B. The chemical composition of comets—emerging taxonomies and natal heritage. Annu. Rev. Astron. Astrophys. 49, 471–524 (2011).

  5. 5.

    Bardyn, A. et al. Carbon-rich dust in comet 67P/Churyumov–Gerasimenko measured by COSIMA/Rosetta. Mon. Not. R. Astron. Soc. 469, S712–S722 (2017).

  6. 6.

    Fray, N. et al. High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko. Nature 538, 72–74 (2016).

  7. 7.

    Altwegg, K. et al. Organics in comet 67P—a first comparative analysis of mass spectra from ROSINA-DFMS, COSAC and Ptolemy. Mon. Not. R. Astron. Soc. 469, S130–S141 (2017).

  8. 8.

    Capaccioni, F. et al. The organic-rich surface of comet 67P/Churyumov–Gerasimenko as seen by VIRTIS/Rosetta. Science 347, aaa0628 (2015).

  9. 9.

    Quirico, E. et al. Refractory and semi-volatile organics at the surface of comet 67P/Churyumov–Gerasimenko: insights from the VIRTIS/Rosetta imaging spectrometer. Icarus 272, 32–47 (2016).

  10. 10.

    Ciarniello, M. et al. Photometric properties of comet 67P/Churyumov–Gerasimenko from VIRTIS-M onboard Rosetta. Astron. Astrophys. 583, A31 (2015).

  11. 11.

    De Sanctis, M. C. et al. The diurnal cycle of water ice on comet 67P/Churyumov–Gerasimenko. Nature 525, 500–503 (2015).

  12. 12.

    Ciarniello, M. et al. The global surface composition of 67P/Churyumov–Gerasimenko nucleus by Rosetta/VIRTIS. II. Diurnal and seasonal variability. Mon. Not. R. Astron. Soc. 462, S443–S458 (2016).

  13. 13.

    Moroz, L. V., Arnold, G., Korochantsev, A. V. & Wäsch, R. Natural solid bitumens as possible analogs for cometary and asteroid organics. 1. Reflectance spectroscopy of pure bitumens. Icarus 134, 253–268 (1998).

  14. 14.

    Sandford, S. A. et al. The interstellar C–H stretching band near 3.4 microns: constraints on the composition of organic material in the diffuse interstellar medium. Astrophys. J. 371, 607–620 (1991).

  15. 15.

    Keller, L. P. et al. The nature of molecular cloud material in interplanetary dust. Geochim. Cosmochim. Acta 68, 2577–2589 (2004).

  16. 16.

    Kaplan, H. H., Milliken, R. E. & Alexander, C. M. O.’D. New constraints on the abundance and composition of organic matter on Ceres. Geophys. Res. Lett. 45, 5274–5282 (2018).

  17. 17.

    Mennella, V. H Atom irradiation of carbon grains under simulated dense interstellar medium conditions: the evolution of organics from diffuse interstellar clouds to the Solar System. Astrophys. J. 718, 867–875 (2010).

  18. 18.

    Pendleton, Y. J., Sandford, S. A., Allamandola, L. J., Tielens, A. G. G. M. & Sellgren, K. Near-infrared absorption spectroscopy of interstellar hydrocarbon grains. Astrophys. J. 437, 683–696 (1994).

  19. 19.

    Dartois, E. et al. Organic matter in Seyfert 2 nuclei: comparison with our Galactic Center lines of sight. Astron. Astrophys. 423, 549–558 (2004).

  20. 20.

    Kebukawa, Y., Alexander, C. M. O.’D. & Cody, G. D. Compositional diversity in insoluble organic matter in type 1, 2 and 3 chondrites as detected by infrared spectroscopy. Geochim. Cosmochim. Acta 75, 3530–3541 (2011).

  21. 21.

    Orthous-Daunay, F.-R. et al. Mid-infrared study of the molecular structure variability of insoluble organic matter from primitive chondrites. Icarus 223, 534–543 (2013).

  22. 22.

    Alexander, C. M. O.’D., Fogel, M., Yabuta, H. & Cody, G. D. The origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter. Geochim. Cosmochim. Acta 71, 4380–4403 (2007).

  23. 23.

    Seok, J. Y. & Li, A. Polycyclic aromatic hydrocarbons in protoplanetary disks around Herbig Ae/Be and T Tauri stars. Astrophys. J. 835, 291 (2017).

  24. 24.

    Muñoz Caro, G. M. & Schutte, W. A. UV-photoprocessing of interstellar ice analogs: new infrared spectroscopic results. Astron. Astrophys. 412, 121–132 (2003).

  25. 25.

    Schutte, W. A. & Khanna, R. K. Origin of the 6.85 μm band near young stellar objects: the ammonium ion (NH4 +) revisited. Astron. Astrophys. 398, 1049–1062 (2003).

  26. 26.

    Brown, M. E. The 3–4 μm spectra of Jupiter trojan asteroids. Astron. J. 152, 159 (2016).

  27. 27.

    Cruikshank, D. P., Dalle Ore, C. M., Clark, R. N. & Pendleton, Y. J. Aromatic and aliphatic organic materials on Iapetus: analysis of Cassini VIMS data. Icarus 233, 306–315 (2014).

  28. 28.

    Rivkin, A. S. & Emery, J. P. Detection of ice and organics on an asteroidal surface. Nature 464, 1322–1323 (2010).

  29. 29.

    Licandro, J. et al. (65) Cybele: detection of small silicate grains, water-ice, and organics. Astron. Astrophys. 525, A34 (2011).

  30. 30.

    Takir, D. & Emery, J. P. Outer main belt asteroids: identification and distribution of four 3 μm spectral groups. Icarus 219, 641–654 (2012).

  31. 31.

    Brown, M. E. & Rhoden, A. R. The 3 μm spectrum of Jupiter’s irregular satellite Himalia. Astrophys. J. Lett. 793, L44 (2014).

  32. 32.

    DeMeo, F. E., Binzel, R. P., Slivan, S. M. & Bus, S. J. An extension of the Bus asteroid taxonomy into the near-infrared. Icarus 202, 160–180 (2009).

  33. 33.

    De Sanctis, M. C. et al. Localized aliphatic organic material on the surface of Ceres. Science 355, 719–722 (2017).

  34. 34.

    De Sanctis, M. C. et al. Characteristics of organic matter on Ceres from VIR/Dawn high spatial resolution spectra. Mon. Not. R. Astron. Soc. 482, 2407–2421 (2019).

  35. 35.

    Morbidelli, A., Levison, H. F. & Gomes, R. in The Solar System Beyond Neptune (eds Barucci, M. A. et al.) 275–292 (Univ. of Arizona Press, 2008).

  36. 36.

    Altwegg, K. et al. 67P/Churyumov–Gerasimenko, a Jupiter family comet with a high D/H ratio. Science 347, 1261952 (2015).

  37. 37.

    Rubin, M. et al. Molecular nitrogen in comet 67P/Churyumov–Gerasimenko indicates a low formation temperature. Science 348, 232–235 (2015).

  38. 38.

    Bertaux, J.-L. & Lallement, R. Diffuse interstellar bands carriers and cometary organic material. Mon. Not. R. Astron. Soc. 469, S646–S660 (2017).

  39. 39.

    Dartois, E. et al. IRAS 08572+3915: constraining the aromatic versus aliphatic content of interstellar HACs. Astron. Astrophys. 463, 635–640 (2007).

  40. 40.

    Keller, L. P. et al. Infrared spectroscopy of comet 81P/Wild 2 samples returned by Stardust. Science 314, 1728–1731 (2006).

  41. 41.

    Sandford, S. A. et al. Organics captured from comet 81P/Wild 2 by the Stardust spacecraft. Science 314, 1720–1724 (2006).

  42. 42.

    Matrajt, G., Flynn, G., Brownlee, D., Joswiak, D. & Bajt, S. The origin of the 3.4 μm feature in Wild 2 cometary particles and in ultracarbonaceous interplanetary dust particles. Astrophys. J. 765, 145 (2013).

  43. 43.

    Ehrenfreund, P. et al. Astrophysical and astrochemical insights into the origin of life. Rep. Prog. Phys. 65, 1427–1487 (2002).

  44. 44.

    Filacchione, G. Calibrazioni a Terra e Prestazioni in Volo di Spettrometri ad Immagine Nel Visibile e Nel Vicino Infrarosso per L’Esplorazione Planetaria. PhD thesis, Univ. degli Studi di Napoli Federico II (2006).

  45. 45.

    Kappel, D., Arnold, G., Haus, R., Piccioni, G. & Drossart, P. Refinements in the data analysis of VIRTIS-M-IR Venus nightside spectra. Adv. Space Res. 50, 228–255 (2012).

  46. 46.

    Stewart, P. N., Tuthill, P. G., Nicholson, P. D., Sloan, G. C. & Hedman, M. M. An atlas of bright star spectra in the near-infrared from Cassini-VIMS. Astrophys. J. Supp. Ser. 221, 30 (2015).

  47. 47.

    Brown, R. H. et al. The Cassini Visual and Infrared Mapping Spectrometer (VIMS) investigation. Space Sci. Rev. 115, 111–168 (2004).

  48. 48.

    Raponi, A. et al. The temporal evolution of exposed water ice-rich areas on the surface of 67P/Churyumov–Gerasimenko: spectral analysis. Mon. Not. R. Astron. Soc. 462, S476–S490 (2016).

  49. 49.

    Hapke, B. Theory of Reflectance and Emittance Spectroscopy 2nd edn (Cambridge Univ. Press, 2012).

  50. 50.

    Warren, S. G. & Brandt, R. E. Optical constants of ice from the ultraviolet to the microwave: a revised compilation. J. Geophys. Res. Atmos. 113, D14220 (2008).

Download references


We thank the Italian Space Agency (ASI, Italy) contract no. I/024/12/2, Centre National d’Etudes Spatiales (CNES, France), DLR (Germany) and NASA (USA) Rosetta programme for supporting this work. The VIRTIS instrument was built by a consortium including Italy, France and Germany under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Italy, which also guides the scientific operations. The VIRTIS instrument development, led by the prime contractor Leonardo Company (Florence, Italy), has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES and from DLR. We thank the Rosetta Science Ground Segment and the Rosetta Mission Operations Centre for their support throughout all phases of the mission. This work takes advantage of the collaboration of the International Space Science Institute international team ‘Comet 67P/Churyumov–Gerasimenko Surface Composition as a Playground for Radiative Transfer Modeling and Laboratory Measurements’, no. 397. We thank D. Takir for providing the reflectance spectra of Europa and Bononia. L.V.M. acknowledges DFG (Deutsche Forschungsgemeinschaft) grant MO 3007/1-1. D.K. acknowledges DFG grant KA 3757/2-1. P.B. acknowledges funding from the H2020 European Research Council (ERC) (SOLARYS ERC-CoG2017_771691). This research has made use of NASA’s Astrophysics Data System Service.

Author information

A.R. wrote the manuscript, calibrated the data and performed data analysis and interpretation. M.C., F.C., V.M., G.F., V.V., P.B., E.Q., M.C.D.S. and L.V.M. contributed to interpretation. G.F. contributed to calibration of the data. All authors helped with the manuscript preparation.

Correspondence to A. Raponi.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–7.

Source data

Source Data Fig. 1

Average infrared spectrum of comet 67P nucleus, after thermal emission removal.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Raponi, A., Ciarniello, M., Capaccioni, F. et al. Infrared detection of aliphatic organics on a cometary nucleus. Nat Astron (2020).

Download citation