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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.

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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 (


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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.

Corresponding author

Correspondence to A. Raponi.

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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.

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Raponi, A., Ciarniello, M., Capaccioni, F. et al. Infrared detection of aliphatic organics on a cometary nucleus. Nat Astron 4, 500–505 (2020).

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Further reading

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