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The highly active Anhur–Bes regions in the 67P/Churyumov–Gerasimenko comet: results from OSIRIS/ROSETTA observations

Sonia Fornasier 1 Clément Feller 1 J.-C. Lee 2 Sabrina Ferrari 3 Matteo Massironi 3, 4 Pedro Henrique Hasselmann 1 J. D. P. Deshapriya 1 Maria Antonella Barucci 1 Mohamed Ramy El-Maarry 5 Lorenza Giacomini 4 Stefano Mottola 6 Horst Uwe Keller 6, 7 Wing-Huen Ip 8, 9 Zhong-Yi Lin 9 Holger Sierks 10 Cesare Barbieri 11 Philippe Lamy 12 Rafael Rodrigo 13 Detlef Koschny 14 Hans Rickman 15, 16 Jessica Agarwal 10 Michael A'Hearn 17 Jean-Loup Bertaux 18 Ivano Bertini 11 Gabriele Cremonese 19 Vania da Deppo 20 Björn Davidsson 21 Stefano Debei 22 Mariolino de Cecco 23 Jakob Deller 10 Marco Fulle 24 Olivier Groussin 12 Pedro J. Gutiérrez 25 Carsten Güttler 10 Marc Hofmann 10 Stubbe F. Hviid 6 Laurent Jorda 12 Jörg Knollenberg 6 Gabor Kovacs 10 Rainer Kramm 10 Ekkehard Kührt 6 Michael Küppers Luisa M. Lara 25 Monica Lazzarin 11 José J. Lopez Moreno 25 Francesco Marzari 11 Giampiero Naletto 20, 4 Nilda Oklay 6 Maurizio Pajola Xian Shi 10 Nicolas Thomas 26 Imre Toth Cécilia Tubiana 10 Jean-Baptiste Vincent 6 
Abstract : The Southern hemisphere of the 67P/Churyumov–Gerasimenko comet has become visible from Rosetta only since 2015 March. It was illuminated during the perihelion passage and therefore it contains the regions that experienced the strongest heating and erosion rates, thus exposing the sub-surface most pristine material. In this work we investigate, thanks to the OSIRIS images, the geomorphology, the spectrophotometry and some transient events of two Southern hemisphere regions: Anhur and part of Bes. Bes is dominated by outcropping consolidated terrain covered with fine particle deposits, while Anhur appears strongly eroded with elongated canyon-like structures, scarp retreats, different kinds of deposits and degraded sequences of strata indicating a pervasive layering. We discovered a new 140 m long and 10 m high scarp formed in the Anhur–Bes boundary during/after the perihelion passage, close to the area where exposed CO2 and H2O ices were previously detected. Several jets have been observed originating from these regions, including the strong perihelion outburst, an active pit and a faint optically thick dust plume. We identify several areas with a relatively bluer slope (i.e. a lower spectral slope value) than their surroundings, indicating a surface composition enriched with some water ice. These spectrally bluer areas are observed especially in talus and gravitational accumulation deposits where freshly exposed material had fallen from nearby scarps and cliffs. The investigated regions become spectrally redder beyond 2 au outbound when the dust mantle became thicker, masking the underlying ice-rich layers.
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Sonia Fornasier, Clément Feller, J.-C. Lee, Sabrina Ferrari, Matteo Massironi, et al.. The highly active Anhur–Bes regions in the 67P/Churyumov–Gerasimenko comet: results from OSIRIS/ROSETTA observations. Monthly Notices of the Royal Astronomical Society, 2017, 469 (Suppl_2), pp.S93 - S107. ⟨10.1093/mnras/stx1275⟩. ⟨insu-01574238⟩



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