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    Geomorphology and spectrophotometry of Philae’s landing site on comet 67P/Churyumov-Gerasimenko

    La Forgia, F. and Giacomini, L. and Lazzarin, M. and Massironi, M. and Oklay, N. and Scholten, F. and Pajola, M. and Bertini, I. and Cremonese, G. and Barbieri, C. and Naletto, G. and Simioni, E. and Preusker, F. and Thomas, N. and Sierks, H. and Lamy, P. and Rodrigo, R. and Koschny, D. and Rickman, H. and Keller, H.U. and Agarwal, J. and Auger, A.-T. and A’Hearn, M.F. and Barucci, M.A. and Bertaux, J.-L. and Besse, S. and Bodewits, D. and Da Deppo, V. and Davidsson, B. and Debei, S. and De Cecco, M. and El-Maarry, Mohamed Ramy and Ferri, F. and Fornasier, S. and Fulle, M. and Groussin, O. and Gutiérrez, P.J. and Güttler, C. and Hall, I. and Hviid, S.F. and Ip, W.-H. and Jorda, L. and Knollenberg, J. and Kramm, J.R. and Kührt, E. and Küppers, M. and Lara, L.-M. and Lopez Moreno, J.J. and Magrin, S. and Marzari, F. and Michalik, H. and Mottola, S. and Pommerol, A. and Tubiana, C. and Vincent, J.-B. (2015) Geomorphology and spectrophotometry of Philae’s landing site on comet 67P/Churyumov-Gerasimenko. Astronomy & Astrophysics 583 , A41. ISSN 0004-6361.

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    Abstract

    Context. On 12 November 2014 the European mission Rosetta succeeded in delivering a lander, named Philae, on the surface of one of the smallest, low-gravity and most primitive bodies of the solar system, the comet 67P/Churyumov-Gerasimenko (67P). Aims. The aim of this paper is to provide a comprehensive geomorphological and spectrophotometric analysis of Philae’s landing site (Agilkia) to give an essential framework for the interpretation of its in situ measurements. Methods. OSIRIS images, coupled with gravitational slopes derived from the 3D shape model based on stereo-photogrammetry were used to interpret the geomorphology of the site. We adopted the Hapke model, using previously derived parameters, to photometrically correct the images in orange filter (649.2 nm). The best approximation to the Hapke model, given by the Akimov parameter-less function, was used to correct the reflectance for the effects of viewing and illumination conditions in the other filters. Spectral analyses on coregistered color cubes were used to retrieve spectrophotometric properties. Results. The landing site shows an average normal albedo of 6.7% in the orange filter with variations of ~15% and a global featureless spectrum with an average red spectral slope of 15.2%/100 nm between 480.7 nm (blue filter) and 882.1 nm (near-IR filter). The spatial analysis shows a well-established correlation between the geomorphological units and the photometric characteristics of the surface. In particular, smooth deposits have the highest reflectance a bluer spectrum than the outcropping material across the area. Conclusions. The featureless spectrum and the redness of the material are compatible with the results by other instruments that have suggested an organic composition. The observed small spectral variegation could be due to grain size effects. However, the combination of photometric and spectral variegation suggests that a compositional differentiation is more likely. This might be tentatively interpreted as the effect of the efficient dust-transport processes acting on 67P. High-activity regions might be the original sources for smooth fine-grained materials that then covered Agilkia as a consequence of airfall of residual material. More observations performed by OSIRIS as the comet approaches the Sun would help interpreting the processes that work at shaping the landing site and the overall nucleus.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): comets: general / comets: individual: 67P/Churyumov-Gerasimenko / methods: data analysis / techniques: photometric
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Administrator
    Date Deposited: 20 Nov 2018 14:06
    Last Modified: 20 Nov 2018 14:06
    URI: http://eprints.bbk.ac.uk/id/eprint/25197

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