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Coma morphology of comet 67P controlled by insolation over irregular nucleus


While the structural complexity of cometary comae is already recognizable from telescopic observations1, the innermost region, within a few radii of the nucleus, was not resolved until spacecraft exploration became a reality2,3. The dust coma displays jet-like features of enhanced brightness superposed on a diffuse background1,4,5. Some features can be traced to specific areas on the nucleus, and result conceivably from locally enhanced outgassing and/or dust emission6,7,8. However, diffuse or even uniform activity over topographic concavity can converge to produce jet-like features9,10. Therefore, linking observed coma morphology to the distribution of activity on the nucleus is difficult11,12. Here, we study the emergence of dust activity at sunrise on comet 67P/Churyumov–Gerasimenko using high-resolution, stereo images from the OSIRIS camera onboard the Rosetta spacecraft, where the sources and formation of the jet-like features are resolved. We perform numerical simulations to show that the ambient dust coma is driven by pervasive but non-uniform water outgassing from the homogeneous surface layer. Physical collimations of gas and dust flows occur at local maxima of insolation and also via topographic focusing. Coma structures are projected to exhibit jet-like features that vary with the perspective of the observer. For an irregular comet such as 67P/Churyumov–Gerasimenko, near-nucleus coma structures can be concealed in the shadow of the nucleus, which further complicates the picture.

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Fig. 1: Observed and synthetic gas and dust emission from morning terminators on 67P.
Fig. 2: Number density of water molecules at different altitudes above the terminator.
Fig. 3: Influence of topography and outgassing flux on near-nucleus coma structure.
Fig. 4: Dust coma in the neck region at the same local time but observed from different perspectives.

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OSIRIS was built by a consortium led by the Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d’Astrophysique de Marseille, France, the Instituto de Astrofísica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Técnica Aeroespacial, Madrid, Spain, the Universidad Politéchnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut für Datentechnik und Kommunikationsnetze der Technischen Universität Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB) and the ESA Technical Directorate is gratefully acknowledged.

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Authors and Affiliations



X.S. led this study, analysed imaging data, performed simulations for gas and dust field modelling, and drafted the manuscript. X.H. contributed to design of the study, performed part of the thermo-physical analysis and contributed to drafting the manuscript. S.M. contributed to the thermo-physical modelling of water activity along dawn terminator and contributed to improving the manuscript. M.R. carried out the development and modification of DSMC code used for cometary coma modelling. H.U.K. and M.F. contributed to interpretation of the results. H.S., C.G. and C.T. participated in early discussions of the study and helped improve the manuscript. S.F., M.P., J.A. and D.B. contributed to improving the manuscript. All remaining authors contributed to the construction, operation and calibration of OSIRIS cameras, which ensured the acquirement of high-quality data used for this study.

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Correspondence to X. Shi.

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Supplementary Information

Supplementary Figures 1–5, Supplementary Table 1, Supplementary Video 1 caption.

Supplementary Video 1

Trajectories of dust particles emitting from the Hapi region observed from a continuously changing perspective.

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Shi, X., Hu, X., Mottola, S. et al. Coma morphology of comet 67P controlled by insolation over irregular nucleus. Nat Astron 2, 562–567 (2018).

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