Volume 586, February 2016
|Number of page(s)||18|
|Section||Planets and planetary systems|
|Published online||02 February 2016|
Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity
1 Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
2 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, Univ. Paris Diderot, Sorbonne Paris Cité, UPMC Univ. Paris 06, 5 place J. Janssen, 92195 Meudon Principal Cedex, France
3 Center of Studies and Activities for Space, CISAS, G. Colombo, University of Padova, via Venezia 15, 35131 Padova, Italy
4 Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
5 Department of Physics & Astronomy, Uppsala University, Box 516 75120 Uppsala, Sweden
6 Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia, 18008 Granada, Spain
7 German Aerospace Center (DLR), Institute of Planetary Research, Berlin-Adlershof, Germany
8 Physikalisches Institut, Sidlerstrasse 5, University of Bern, 3012 Bern, Switzerland
9 Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy
10 CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
11 Dipartimento di Fisica e Astronomia Galileo Galilei, University of Padova, vic. Osservatorio 3, 35122 Padova, Italy
12 Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astro-physique de Marseille) UMR 7326, 13388 Marseille, France
13 Centro de Astrobiologia (INTA-CSIC), European Space Agency (ESA), European Space Astronomy Centre (ESAC), PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
14 International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
15 PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
16 Department for Astronomy, University of Maryland, College Park, MD 20742-2421, USA
17 Gauss Professor Akademie der Wissenschaften zu Göttingen, 37077 Göttingen, Germany
18 LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
19 INAF Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
20 Department of Industrial Engineering University of Padova via Venezia, 1, 35131 Padova, Italy
21 University of Trento, via Sommarive, 9, 38123 Trento, Italy
22 INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
23 Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
24 Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
25 ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
26 Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary
Received: 15 September 2015
Accepted: 5 December 2015
Aims.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.
Key words: comets: individual: 67P/Churyumov-Gerasimenko / methods: data analysis / techniques: image processing / techniques: imaging spectroscopy
© ESO, 2016
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