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Rosetta/OSIRIS observations of 67P nucleus during the April 2016 flyby: high-resolution spectrophotometry

Clément Feller 1 Sonia Fornasier 1 Sabrina Ferrari 2 Pedro Henrique Hasselmann 1 Antonella M. Barucci 1 Matteo Massironi 2 J. D. P. Deshapriya 1 Holger Sierks 3 Giampiero Naletto 4, 2, 5 Philippe Lamy 6 Rafael Rodrigo 7, 8 Detlef Koschny 9 Björn Davidsson 10 Jean-Loup Bertaux 6 Ivano Bertini 4 Dennis Bodewits 11 Gabriele Cremonese 12 Vania da Deppo 13 Stefano Debei 14 Maurizio de Cecco 15 Marco Fulle 16 Pedro J. Gutiérrez 17 Carsten Güttler 3 Wing-Huen Ip 18, 19 Horst U. Keller 20, 21 Luisa-Maria Lara 17 Monica Lazzarin 11 Josè Juan Lopez-Moreno 17 Francesco Marzari 4 Xian Shi 3 Cécilia Tubiana 3 B. Gaskell 22 Florangela La Forgia 4 A. Lucchetti 12 Sefano Mottola 21 Maurizio Pajola 12 Frank Preusker 21 Frank Scholten 21 
Abstract : From August 2014 to September 2016, the Rosetta spacecraft followed comet 67P/Churyumov–Gerasimenko along its orbit. After the comet passed perihelion, Rosetta performed a flyby manoeuvre over the Imhotep–Khepry transition in April 2016. The OSIRIS/Narrow-Angle-Camera (NAC) acquired 112 observations with mainly three broadband filters (centered at 480, 649, and 743 nm) at a resolution of up to 0.53 m/px and for phase angles between 0.095° and 62°. We have investigated the morphological and spectrophotometrical properties of this area using the OSIRIS/NAC high-resolution observations. We assembled the observations into coregistered color cubes. Using a 3D shape model, we produced the illumination conditions and georeference for each observation. We mapped the observations of the transition to investigate its geomorphology. Observations were photometrically corrected using the Lommel–Seeliger disk law. Spectrophotometric analyses were performed on the coregistered color cubes. These data were used to estimate the local phase reddening. The Imhotep–Khepry transition hosts numerous and varied types of terrains and features. We observe an association between a feature’s nature, its reflectance, and its spectral slopes. Fine material deposits exhibit an average reflectance and spectral slope, while terrains with diamictons, consolidated material, degraded outcrops, or features such as somber boulders present a lower-than-average reflectance and higher-than-average spectral slope. Bright surfaces present here a spectral behavior consistent with terrains enriched in water-ice. We find a phase-reddening slope of 0.064 ± 0.001%/100 nm/° at 2.7 au outbound, similar to the one obtained at 2.3 au inbound during the February 2015 flyby. Identified as the source region of multiple jets and a host of water-ice material, the Imhotep–Khepry transition appeared in April 2016, close to the frost line, to further harbor several potential locations with exposed water-ice material among its numerous different morphological terrain units.
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Clément Feller, Sonia Fornasier, Sabrina Ferrari, Pedro Henrique Hasselmann, Antonella M. Barucci, et al.. Rosetta/OSIRIS observations of 67P nucleus during the April 2016 flyby: high-resolution spectrophotometry. Astronomy and Astrophysics - A&A, EDP Sciences, 2019, 630, A9 (20p.). ⟨10.1051/0004-6361/201833807⟩. ⟨insu-02115740⟩



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