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Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity

Björn J. R. Davidsson 1 Pedro J. Gutiérrez 2 Holger Sierks 3 Cesare Barbieri 4 Philippe L. Lamy 5 Rafael Rodrigo 6 Detlef Koschny 7 Hans Rickman 1 Horst Uwe Keller 8 J. Agarwal Michael F. A'Hearn 3 Antonella M. Barucci 9 Jean-Loup Bertaux 10 Ivano Bertini 11 Dennis Bodewits 12 Gabriele Cremonese 13 Vania da Deppo 14 Stefano Debei 15 Mariolino de Cecco 16 Sonia Fornasier 9 Marco Fulle 17 Olivier Groussin 5 Carsten Güttler 3 S. F. Hviid 18 W.-H. Ip 19 Laurent Jorda 5 J. Knollenberg 18 Gabor Kovacs 3 J.-R. Kramm 3 Ekkehard Kührt 18 M. Küppers 20 F. La Forgia Luisa M. Lara 2 Monica Lazzarin 4 Jose J. Lopez Moreno 2 S. Lowry S. Magrin F. Marzari 4 H. Michalik Richard Moissl-Fraund Giampiero Naletto 11 Nilda Oklay 3 Maurizio Pajola 11 Collin Snodgrass Nicholas Thomas 21 C. Tubiana 3 Jean-Baptiste Vincent 3
Abstract : We carried out an investigation of the surface variegation of comet 67P/Churyumov-Gerasimenko, the detection of regions showing activity, the determination of active and inactive surface regions of the comet with spectral methods, and the detection of fallback material. Methods. We analyzed multispectral data generated with Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) narrow angle camera (NAC) observations via spectral techniques, reflectance ratios, and spectral slopes in order to study active regions. We applied clustering analysis to the results of the reflectance ratios, and introduced the new technique of activity thresholds to detect areas potentially enriched in volatiles. Results. Local color inhomogeneities are detected over the investigated surface regions. Active regions, such as Hapi, the active pits of Seth and Ma’at, the clustered and isolated bright features in Imhotep, the alcoves in Seth and Ma’at, and the large alcove in Anuket, have bluer spectra than the overall surface. The spectra generated with OSIRIS NAC observations are dominated by cometary emissions of around 700 nm to 750 nm as a result of the coma between the comet’s surface and the camera. One of the two isolated bright features in the Imhotep region displays an absorption band of around 700 nm, which probably indicates the existence of hydrated silicates. An absorption band with a center between 800–900 nm is tentatively observed in some regions of the nucleus surface. This absorption band can be explained by the crystal field absorption of Fe2+, which is a common spectral feature seen in silicates.
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Björn J. R. Davidsson, Pedro J. Gutiérrez, Holger Sierks, Cesare Barbieri, Philippe L. Lamy, et al.. Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity. Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 586, A80 (18 p.). ⟨10.1051/0004-6361/201527369⟩. ⟨insu-01273847⟩

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