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)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 Department of Atmospheric Sciences [Taoyuan City]
3 Dipartimento di Geoscienze [Padova]
4 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
5 LASP - Laboratory for Atmospheric and Space Physics [Boulder]
6 DLR Institut für Planetenforschung
7 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
8 SSI - Space Science Institute [Macau]
9 IANCU - Institute of Astronomy [Taiwan]
10 MPS - Max-Planck-Institut für Sonnensystemforschung
11 Dipartimento di Fisica e Astronomia "Galileo Galilei"
12 LAM - Laboratoire d'Astrophysique de Marseille
13 CAB - Centro de Astrobiologia [Madrid]
14 ESTEC - European Space Research and Technology Centre
15 Department of Physics and Astronomy [Uppsala]
16 CBK - Space Research Centre of Polish Academy of Sciences
17 Department of Astronomy [College Park]
18 PLANETO - LATMOS
19 OAPD - INAF - Osservatorio Astronomico di Padova
20 IFN - CNR Institute for Photonics and Nanotechnologies
21 JPL - Jet Propulsion Laboratory
22 Department of Industrial Engineering [Padova]
23 University of Trento [Trento]
24 OAT - INAF - Osservatorio Astronomico di Trieste
25 IAA - Instituto de Astrofísica de Andalucía
26 Physikalisches Institut [Bern]

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.

Domains: Solar and Stellar Astrophysics [astro-ph.SR]; Earth and Planetary Astrophysics [astro-ph.EP]; Instrumentation and Methods for Astrophysic [astro-ph.IM]; Physics [physics]; Astrophysics [astro-ph]

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⟩