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


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.

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Figure 1: DFMS mass spectra around 32 Da/e normalized to the spectrum with the largest signal.
Figure 2: Correlation between H2O and O2, CO and N2.
Figure 3: O2/H2O ratio over several months.
Figure 4: DFMS spectra for some of the common products of radiolysis of water ice.

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Work at the University of Michigan was funded by NASA contract JPL-1266313. Work at the University of Bern was funded by the State of Bern, the Swiss National Science Foundation and the European Space Agency PRODEX Program. Work at Max-Planck-Institut für Sonnensystemforschung was funded by the Max-Planck Society and BMWI contract 50QP1302. Work at Southwest Research Institute was supported by subcontract 1496541 from the Jet Propulsion Laboratory. Work at BIRA-IASB was supported by the Belgian Science Policy Office via PRODEX/ROSINA PEA 90020. This work was carried out thanks to the support of the A*MIDEX project (no. ANR-11-IDEX-0001-02) funded by the ‘Investissements d’Avenir’ French Government programme, managed by the French National Research Agency (ANR). This work was supported by CNES grants at IRAP, LATMOS, LPC2E, UTINAM, CRPG, and by the European Research Council (grant no. 267255 to B.M.). A.B.-N. thanks the Ministry of Science and the Israel Space agency. Work by J.H.W. at Southwest Research Institute was funded by NASA JPL subcontract NAS703001TONMO710889. E.F.v.D. and C.W. are supported by A-ERC grant 291141 CHEMPLAN and an NWO Veni award. We acknowledge here the work of the whole ESA Rosetta team.

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Authors and Affiliations



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.

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Correspondence to A. Bieler.

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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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Bieler, A., Altwegg, K., Balsiger, H. et al. Abundant molecular oxygen in the coma of comet 67P/Churyumov–Gerasimenko. Nature 526, 678–681 (2015).

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