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Title: | Spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from the OSIRIS instrument onboard the ROSETTA spacecraft | Authors: | Fornasier, S. Hasselmann, P. H. Barucci, M. A. Feller, C. Besse, S. Leyrat, C. Lara, L. Gutierrez, P. J. Oklay, N. Tubiana, C. Scholten, F. Sierks, H. Barbieri, C. Lamy, P. L. Rodrigo, R. Koschny, D. Rickman, H. Keller, H. U. Agarwal, J. A'Hearn, M. F. Bertaux, J. -L. Bertini, I. CREMONESE, Gabriele Da Deppo, V. Davidsson, B. Debei, S. De Cecco, M. FULLE, Marco Groussin, O. Güttler, C. Hviid, S. F. Ip, W. Jorda, L. Knollenberg, J. Kovacs, G. Kramm, R. Kührt, E. Küppers, M. La Forgia, F. Lazzarin, M. Lopez Moreno, J. J. Marzari, F. Matz, K. -D. Michalik, H. Moreno, F. Mottola, S. Naletto, G. PAJOLA, MAURIZIO Pommerol, A. Preusker, F. Shi, X. Snodgrass, C. Thomas, N. Vincent, J. -B. |
Issue Date: | 2015 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 583 | First Page: | A30 | Abstract: | Context. 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. <BR /> 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. <BR /> 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. <BR /> 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 H<SUB>v</SUB>(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 SO<SUB>2</SUB> 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. <P />Table 1 is available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201525901/olm">http://www.aanda.org</A> | Acknowledgments: | OSIRIS was built by a consortium of the Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany, CISAS–University of Padova, Italy, the Laboratoire d’Astrophysique de Marseille, France, the Instituto de Astrofísica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department 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. We thank the referee, J.-Y. Li, for his comments and suggestions that helped to improve this manuscript. | URI: | http://hdl.handle.net/20.500.12386/23144 | URL: | https://www.aanda.org/articles/aa/abs/2015/11/aa25901-15/aa25901-15.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201525901 | Bibcode ADS: | 2015A&A...583A..30F | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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