Spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from the OSIRIS instrument onboard the Rosetta spacecraft

Sonia Fornasier 1, 2 P. H. Hasselmann 2, 3 M.A. Barucci 2 C. Feller 1, 2 S. Besse 4 C. Leyrat 2 Luisa M. Lara 5 Pedro J. Gutierrez 5 Nilda Oklay 6 Cécilia Tubiana 6 F. Scholten 7 Holger Sierks 6 Cesare Barbieri 8 Philippe L. Lamy 9 Rafael Rodrigo 10, 11 Detlef Koschny 4 Hans Rickman 12, 13 Horst U. Keller 14 Jessica Agarwal 6 Michael F. A’hearn 15 Jean-Loup Bertaux 16 Ivano Bertini 17 Gabriele Cremonese 18 Vania Da Deppo 19 Björn Davidsson 13 Stefano Debei 20 Mariolino De Cecco 21 Marco Fulle 22 Olivier Groussin 9 Carsten Güttler 6 Stubbe F. Hviid 7 W.-H. Ip 23 Laurent Jorda 9 Jörg Knollenberg 7 G. Kovacs 6 J.-R. Kramm 6 Ekkehard Kührt 7 Michael Küppers 24 Florangela La Forgia 8 M. Lazzarin 8 Jose J. Lopez Moreno 5 Francesco Marzari 8 K.-D. Matz 7 Harald Michalik 25 F. Moreno 5 Stefano Mottola 7 Giampiero Naletto 26, 17, 19 M. Pajola 17 A. Pommerol 27 F. Preusker 7 X. Shi 6 Colin Snodgrass 6, 28 Nicholas Thomas 27 Jean-Baptiste Vincent 6
Abstract : The Rosetta mission of the European Space Agency has been orbiting the comet 67P/Churyumov-Gerasimenko (67P) since August 2014 and is now in its escort phase. A large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted are onboard Rosetta. Aims. We present results for the photometric and spectrophotometric properties of the nucleus of 67P derived from the OSIRIS imaging system, which consists of a Wide Angle Camera (WAC) and a Narrow Angle Camera (NAC). The observations presented here were performed during July and the beginning of August 2014, during the approach phase, when OSIRIS was mapping the surface of the comet with several filters at different phase angles (1.3°–54°). The resolution reached up to 2.1 m/px. Methods. The OSIRIS images were processed with the OSIRIS standard pipeline, then converted into I/F radiance factors and corrected for the illumination conditions at each pixel using the Lommel-Seeliger disk law. Color cubes of the surface were produced by stacking registered and illumination-corrected images. Furthermore, photometric analysis was performed both on disk-averaged photometry in several filters and on disk-resolved images acquired with the NAC orange filter, centered at 649 nm, using Hapke modeling. Results. The disk-averaged phase function of the nucleus of 67P shows a strong opposition surge with a G parameter value of - 0.13±0.01 in the HG system formalism and an absolute magnitude Hv (1, 1, 0) = 15.74±0.02 mag. The integrated spectrophotometry in 20 filters covering the 250-1000 nm wavelength range shows a red spectral behavior, without clear absorption bands except for a potential absorption centered at ∼ 290 nm that is possibly due to SO2 ice. The nucleus shows strong phase reddening, with disk- averaged spectral slopes increasing from 11%/(100 nm) to 16%/(100 nm) in the 1.3°–54° phase angle range. The geometric albedo of the comet is 6.5±0.2% at 649 nm, with local variations of up to ∼ 16% in the Hapi region. From the disk-resolved images we computed the spectral slope together with local spectrophotometry and identified three distinct groups of regions (blue, moderately red, and red). The Hapi region is the brightest, the bluest in term of spectral slope, and the most active surface on the comet. Local spectrophotometry shows an enhancement of the flux in the 700-750 nm that is associated with coma emissions.
Type de document :
Article dans une revue
Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 583, A30 (18 p.). <10.1051/0004-6361/201525901>
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Soumis le : samedi 26 septembre 2015 - 14:00:10
Dernière modification le : jeudi 20 juillet 2017 - 09:30:34

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Sonia Fornasier, P. H. Hasselmann, M.A. Barucci, C. Feller, S. Besse, et al.. Spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from the OSIRIS instrument onboard the Rosetta spacecraft. Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 583, A30 (18 p.). <10.1051/0004-6361/201525901>. <insu-01205664>

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