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)

1 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 Department of Astronomy [College Park]
3 DLR Institut für Planetenforschung
4 MPS - Max-Planck-Institut für Sonnensystemforschung
5 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
6 Dipartimento di Fisica e Astronomia "Galileo Galilei"
7 IFN - CNR Istituto di Fotonica e Nanotecnologie [Padova]
8 PLANETO - LATMOS
9 CAB - Centro de Astrobiologia [Madrid]
10 ISSI - International Space Science Institute [Bern]
11 ESTEC - European Space Research and Technology Centre
12 JPL - Jet Propulsion Laboratory
13 IKI - Space Research Institute of the Russian Academy of Sciences
14 Department of Physics [Auburn]
15 OAPD - INAF - Osservatorio Astronomico di Padova
16 IFN - CNR Institute for Photonics and Nanotechnologies
17 Department of Mechanical Engineering [Padova]
18 University of Trento [Trento]
19 Dipartimento di Geoscienze [Padova]
20 OAT - INAF - Osservatorio Astronomico di Trieste
21 IAA - Instituto de Astrofísica de Andalucía
22 IANCU - Institute of Astronomy [Taiwan]
23 SSI - Space Science Institute [Macau]
24 LAM - Laboratoire d'Astrophysique de Marseille
25 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
26 ESAC - European Space Astronomy Centre
27 Konkoly Observatory

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.

Keywords: comets: individual: 67P/Churyumov-Gerasimenko; methods: data analysis; methods: observational; techniques: photometric; techniques: imaging spectroscopy

Domains: Astrophysics [astro-ph]; Physics [physics]; Astrophysics [astro-ph]

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, 2019, Rosetta mission full comet phase results, 630, pp.A13. ⟨10.1051/0004-6361/201834824⟩. ⟨insu-02114680⟩