Abundant molecular oxygen in the coma of comet 67P/Churyumov–Gerasimenko

Journal name:
Nature
Volume:
526,
Pages:
678–681
Date published:
DOI:
doi:10.1038/nature15707
Received
Accepted
Published online

The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density1. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn2, 3, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov–Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet’s formation, which is unexpected given the low upper limits from remote sensing observations4. Current Solar System formation models do not predict conditions that would allow this to occur.

At a glance

Figures

  1. DFMS mass spectra around 32 Da/e normalized to the spectrum with the largest signal.
    Figure 1: DFMS mass spectra around 32 Da/e normalized to the spectrum with the largest signal.

    The black labels indicate the three major species found in the coma of 67P at 32 Da/e. The green labels and green line identify contamination peaks from thruster firings, showing that their contributions to the O2 peak are very low. The light blue, dark blue and purple lines represent measurements taken at different distances from the comet nucleus.

  2. Correlation between H2O and O2, CO and N2.
    Figure 2: Correlation between H2O and O2, CO and N2.

    a, H2O and O2; b, H2O and CO; c, H2O and N2. All three panels share a common y axis. Numbers on x and y axes are proportional to number density but in arbitrary units. Red crosses mark a subset of data for which N2 data are also available. Panel a shows the strong correlation between H2O and O2, which is observed for all data. In contrast, the correlation of CO with H2O (b) varies over time, which leads to a low overall correlation between those two species. N2 has the lowest correlation with H2O of the compared species for the October data (c).

  3. O2/H2O ratio over several months.
    Figure 3: O2/H2O ratio over several months.

    There seems to be no systematic increase or decrease of the O2/H2O ratio. The variances happen on very short timescales and can be explained by the decrease of the O2 ratio for high H2O abundances. It is not fully understood if the higher variability of the O2 ratio from October to the end of December 2014 can be attributed to orbital changes of the spacecraft or to physical changes of the cometary nucleus.

  4. DFMS spectra for some of the common products of radiolysis of water ice.
    Figure 4: DFMS spectra for some of the common products of radiolysis of water ice.

    ac, Products are O2H (seen in a), 16O18O and O2H2 (seen in b) and O3 (not seen in c). These data were recorded on 20 October 2014 at around 01:00 utc. With the exception of O3 (c), all the previously mentioned species are measured and can clearly be identified in the mass spectra of DFMS. The grey area consists of the statistical error and a 10% uncertainty from the individual pixel gains on the detector (here N is the number of molecules on the detector).

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Author information

Affiliations

  1. Department of Climate and Space Science and Engineering, University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109, USA

    • A. Bieler,
    • M. Combi,
    • T. I. Gombosi &
    • K. C. Hansen
  2. Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

    • A. Bieler,
    • K. Altwegg,
    • H. Balsiger,
    • P. Bochsler,
    • U. Calmonte,
    • S. Gasc,
    • M. Hässig,
    • A. Jäckel,
    • E. Kopp,
    • M. Rubin,
    • T. Sémon,
    • C.-Y. Tzou &
    • P. Wurz
  3. Center for Space and Habitability, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

    • K. Altwegg,
    • L. Le Roy &
    • P. Wurz
  4. Department of Geosciences, Tel-Aviv University, Ramat-Aviv, 6997801 Tel-Aviv, Israel

    • A. Bar-Nun
  5. LATMOS/IPSL-CNRS-UPMC-UVSQ, 4 Avenue de Neptune, F-94100 Saint-Maur, France

    • J.-J. Berthelier
  6. Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 6115 CNRS – Université d’Orléans, 45071 Orléans, France

    • C. Briois
  7. Belgian Institute for Space Aeronomy, BIRA-IASB, Ringlaan 3, B-1180 Brussels, Belgium

    • J. De Keyser &
    • R. Maggiolo
  8. Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

    • E. F. van Dishoeck &
    • C. Walsh
  9. Institute of Computer and Network Engineering (IDA), TU Braunschweig, Hans-Sommer-Straße 66, D-38106 Braunschweig, Germany

    • B. Fiethe
  10. Space Science and Engineering Division, Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas 78228, USA

    • S. A. Fuselier,
    • M. Hässig &
    • J. H. Waite
  11. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany

    • A. Korth &
    • U. Mall
  12. Centre de Recherches Pétrographiques et Géochimiques, CRPG-CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, 54501 Vandoeuvre lès Nancy, France

    • B. Marty
  13. Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France

    • O. Mousis
  14. Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA

    • T. Owen
  15. Université de Toulouse–UPS-OMP–IRAP, 31400 Toulouse, France

    • H. Rème
  16. CNRS–IRAP, 9 avenue du Colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France

    • H. Rème

Contributions

A.B. performed data reduction, analysis and wrote the paper; K.A. initialized and edited the paper and contributed to data interpretation; C.B., U.C., M.C., T.I.G., K.C.H., S.G., M.H., A.J., R.M., L.L.R., M.R., C.-Y.T. and T.S. contributed to data analysis and interpretation. A.B.-N. and O.M. contributed to data interpretation relevant to processes in ices. E.F.v.D and C.W. contributed to data interpretation and writing of sections concerning interstellar oxygen. H.B., J.-J.B., P.B., J.D.K., B.F., S.A.F., A.K., U.M., B.M., T.O., H.R., J.H.W. and P.W. contributed to experiment design, calibration and data interpretation. All authors discussed the results, and commented on and revised the manuscript.

Competing financial interests

The authors declare no competing financial interests.

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All ROSINA-DFMS data will be released to the PSA archive of ESA and to the PDS archive of NASA.

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