Surface evolution of the Anhur region on comet 67P/Churyumov-Gerasimenko from high-resolution OSIRIS images

Sonia Fornasier 1 Clément Feller 1 Pedro H. Hasselmann 1 Maria Antonella Barucci 1 J. Sunshine 2 Jean-Baptiste Vincent 3 X. Shi 4 Holger Sierks 4 Giampiero Naletto 5, 6, 7 Philippe Lamy 8 Rafael Rodrigo 9, 10 Detlef Koschny 11 Björn Davidsson 12 Jean-Loup Bertaux 8, 13 Ivano Bertini 6 Dennis Bodewits 14 Gabriele Cremonese 15 Vania da Deppo 16 Stefano Debei 17 Mariolino de Cecco 18 Jakob Deller 4 S. Ferrari 19 Marco Fulle 20 Pedro J. Gutiérrez 21 Carsten Guttler 4 W.-H. Ip 22, 23 Laurent Jorda 24 Horst U. Keller 25, 26 Luisa-Maria Lara 21 Monica Lazzarin 6 Josè Juan Lopez-Moreno 21 Alice Lucchetti 15 Francesco Marzari 6 Stefano Mottola 3 Maurizio Pajola 15 I. Toth 27 Cécilia Tubiana 4
Abstract : The southern hemisphere of comet 67P/Churyumov-Gerasimenko (67P) became observable by the Rosetta mission in March 2015, a few months before cometary southern vernal equinox. The Anhur region in the southern part of the comet’s larger lobe was found to be highly eroded, enriched in volatiles, and highly active. We analyze high-resolution images of the Anhur region pre- and post-perihelion acquired by the OSIRIS imaging system on board the Rosetta mission. The Narrow Angle Camera is particularly useful for studying the evolution in Anhur in terms of morphological changes and color variations. Radiance factor images processed by the OSIRIS pipeline were coregistered, reprojected onto the 3D shape model of the comet, and corrected for the illumination conditions. We find a number of morphological changes in the Anhur region that are related to formation of new scarps; removal of dust coatings; localized resurfacing in some areas, including boulders displacements; and vanishing structures, which implies localized mass loss that we estimate to be higher than 50 million kg. The strongest changes took place in and nearby the Anhur canyon-like structure, where significant dust cover was removed, an entire structure vanished, and many boulders were rearranged. All such changes are potentially associated with one of the most intense outbursts registered by Rosetta during its observations, which occurred one day before perihelion passage. Moreover, in the niche at the foot of a new observed scarp, we also see evidence of water ice exposure that persisted for at least six months. The abundance of water ice, evaluated from a linear mixing model, is relatively high (>20%). Our results confirm that the Anhur region is volatile-rich and probably is the area on 67P with the most pristine exposures near perihelion.
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Sonia Fornasier, Clément Feller, Pedro H. Hasselmann, Maria Antonella Barucci, J. Sunshine, et al.. Surface evolution of the Anhur region on comet 67P/Churyumov-Gerasimenko from high-resolution OSIRIS images. Astronomy and Astrophysics - A&A, EDP Sciences, 2019, Rosetta mission full comet phase results, 630, pp.A13. ⟨10.1051/0004-6361/201834824⟩. ⟨insu-02114680⟩

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