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Comet 67P/Churyumov-Gerasimenko sheds dust coat accumulated over the past four years

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Abstract

Comets are composed of dust and frozen gases. The ices are mixed with the refractory material either as an icy conglomerate1, or as an aggregate of pre-solar grains (grains that existed prior to the formation of the Solar System), mantled by an ice layer2,3. The presence of water-ice grains in periodic comets is now well established4,5,6. Modelling of infrared spectra obtained about ten kilometres from the nucleus of comet Hartley 2 suggests that larger dust particles are being physically decoupled from fine-grained water-ice particles that may be aggregates7, which supports the icy-conglomerate model. It is known that comets build up crusts of dust that are subsequently shed as they approach perihelion8,9,10. Micrometre-sized interplanetary dust particles collected in the Earth’s stratosphere and certain micrometeorites are assumed to be of cometary origin11,12,13. Here we report that grains collected from the Jupiter-family comet 67P/Churyumov-Gerasimenko come from a dusty crust that quenches the material outflow activity at the comet surface14. The larger grains (exceeding 50 micrometres across) are fluffy (with porosity over 50 per cent), and many shattered when collected on the target plate, suggesting that they are agglomerates of entities in the size range of interplanetary dust particles. Their surfaces are generally rich in sodium, which explains the high sodium abundance in cometary meteoroids15. The particles collected to date therefore probably represent parent material of interplanetary dust particles. This argues against comet dust being composed of a silicate core mantled by organic refractory material and then by a mixture of water-dominated ices2,3. At its previous recurrence (orbital period 6.5 years), the comet’s dust production doubled when it was between 2.7 and 2.5 astronomical units from the Sun14, indicating that this was when the nucleus shed its mantle. Once the mantle is shed, unprocessed material starts to supply the developing coma, radically changing its dust component, which then also contains icy grains, as detected during encounters with other comets closer to the Sun4,5.

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Figure 1: Dust particles.

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Change history

  • 11 February 2015

    A minor typo relating to ref. 29 was corrected.

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Acknowledgements

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, the Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften, Graz, Austria and is led by the Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany. The support of the national funding agencies of Germany (DLR, grant 50 QP 1302), France (CNES), Austria, Finland and the ESA Technical Directorate is gratefully acknowledged. S.S. acknowledges the support by the Swedish National Space Board grant (contract number 121/11). 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 science return of the Rosetta mission.

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Contributions

M.H. managed the project. J.K., Y.L., J.S., K.H., L.T., J.R., K.V. and R.S. contributed to instrument development. J.R., M.H., H.F., Y.L., J.P., L.T., and O.S. contributed to instrument operations and data distribution. C.B., C.E., D.B., A.B., H.C., N.F., M.G., J.K., K.H., H.L., Y.L., L.L.R., F.-R.O.-D., S.M., J.R., J.S., S.S., L.T., B.Z. and M.H. contributed to instrument and data calibration. Y.L. provided grain images and the porosity value. C.E. provided calibrated mass spectrometry data. R.S. performed comet research and wrote the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Rita Schulz.

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The authors declare no competing financial interests.

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After the proprietary period of six months the data will be available in the ESA Planetary Science Archive (http://www.rssd.esa.int/index.php?project=PSA).

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Schulz, R., Hilchenbach, M., Langevin, Y. et al. Comet 67P/Churyumov-Gerasimenko sheds dust coat accumulated over the past four years. Nature 518, 216–218 (2015). https://doi.org/10.1038/nature14159

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