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

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Université, 5 Place J. Janssen, 92195 Meudon Pricipal Cedex, France
e-mail: sonia.fornasier@obspm.fr
² Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
³ Deutsches Zentrum für Luft und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstrasse 2, 12489 Berlin, Germany
⁴ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077 Göttingen, Germany
⁵ Department of Physics and Astronomy Galileo Galilei, University of Padova, Via Marzolo 8, 35131 Padova, Italy
⁶ Center of Studies and Activities for Space (CISAS) G. Colombo, University of Padova, Via Venezia 15, 35131 Padova, Italy
⁷ CNR-IFN UOS Padova LUXOR, Via Trasea, 7, 35131 Padova, Italy
⁸ Laboratoire Atmosphères, Milieux et Observations Spatiales, CNRS & Université de Versailles Saint-Quentin-en-Yvelines, 11 boulevard d’Alembert, 78280 Guyancourt, France
⁹ Centro de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain
¹⁰ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
¹¹ Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands
¹² Jet Propulsion Laboratory, M/S 183-401, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹³ Physics Department, Auburn University, 206 Allison Laboratory, Auburn, AL 36849, USA
¹⁴ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁵ Department of Mechanical Engineering, University of Padova, Via Venezia 1, 35131 Padova, Italy
¹⁶ Faculty of Engineering, University of Trento, Via Mesiano 77, 38100 Trento, Italy
¹⁷ Dipartimento di Geoscienze, University of Padova, Via G. Gradenigo 6, 35131 Padova, Italy
¹⁸ INAF Astronomical Observatory of Trieste, Via Tiepolo 11, 34014 Trieste, Italy
¹⁹ Instituto de Astrofísica de Andalucia (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain
²⁰ Graduate Institute of Astronomy, National Central University, 300 Chung-Da Rd, Chung-Li 32054, Taiwan
²¹ Space Science Institute, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau
²² Laboratoire d’Astrophysique de Marseille, UMR 7326 CNRS, Université Aix-Marseille, 38 r ue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
²³ Institut für Geophysik und extraterrestrische Physik (IGEP), Technische Universitat Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
²⁴ Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
²⁵ MTA CSFK Konkoly Observatory, Budapest, Hungary

Received: 11 December 2018
Accepted: 5 March 2019

Abstract

Context. 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.

Aims. 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.

Methods. 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.

Results. 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.