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

Nilda Oklay 1 Jean-Baptiste Vincent 1 Sonia Fornasier 2 Maurizio Pajola 3 Sebastien Besse 4 Björn J. R. Davidsson 5 Luisa M. Lara 6 Stefano Mottola 7 Giampiero Naletto 3, 8 Holger Sierks 1 Antonella M. Barucci 2 Frank Scholten 7 Frank Preusker 7 Antoine Pommerol 9 Nafiseh Masoumzadeh 1 Monica Lazzarin 10 Cesare Barbieri 10 Philippe L. Lamy 11 Rafael Rodrigo 12, 13 Detlef Koschny 4 Hans Rickman 5, 14 Michael F. A'Hearn 1, 15, 16 Jean-Loup Bertaux 17 Ivano Bertini 3 Dennis Bodewits 15 Gabriele Cremonese 18 Vania da Deppo 19 Stefano Debei 20 Mariolino de Cecco 21 Marco Fulle 22 Olivier Groussin 11 Pedro J. Gutiérrez 6 Carsten Güttler 1 I. Hall 1 M. Hofmann 1 S. F. Hviid 7 W.-H. Ip 23 Laurent Jorda 11 Horst Uwe Keller 24 J. Knollenberg 7 Gabor Kovacs 1 J.-R. Kramm 1 Ekkehard Kührt 7 M. Küppers 25 Z.-Y. Lin 26 Jose J. Lopez Moreno 6 F. Marzari 10 F. Moreno 6 X. Shi 1 Nicholas Thomas 9 Imre Toth 11, 27 C. Tubiana 1
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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Submitted on : Sunday, February 14, 2016 - 2:44:26 PM
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Nilda Oklay, Jean-Baptiste Vincent, Sonia Fornasier, Maurizio Pajola, Sebastien Besse, 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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