Physical properties and dynamical relation of the circular depressions on comet 67P/Churyumov-Gerasimenko

¹ Institute of Astronomy, National Central University, 32054 Chung-Li, Taiwan
e-mail: wingip@astro.ncu.edu.tw
² Institute of Space Sciences, National Central University, 32054 Chung-Li, Taiwan
³ Space Science Institute, Macau University of Science and Technology, Macau
⁴ Dept. of Earth Science, National Central University, 32054 Chung-Li, Taiwan
⁵ Max-Planck Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077 Göttingen, Germany
⁶ Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
⁷ Department of Physics and Astronomy “G. Galilei”, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁸ Centro di Ateneo di Studi ed Attivitá Spaziali “Giuseppe Colombo”, University of Padova, via Venezia 15, 35131 Padova, Italy
⁹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astro-physique de Marseille) UMR 7326, 13388 Marseille, France
¹⁰ Centro de Astrobiologia (INTA-CSIC), Madrid, Spain
¹¹ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
¹² Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹³ PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
¹⁴ Institut für Geophysik und extraterrestrische Physik (IGEP), Technische Universität Braunschweig, 38106 Braunschweig, Germany
¹⁵ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
¹⁶ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon Principal Cedex, France
¹⁷ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁸ INAF Osservatorio Astronomico di Padova, vic. dell Osservatorio 5, 35122 Padova, Italy
¹⁹ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
²⁰ Department of Industrial Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy
²¹ University of Trento, via Sommarive 9, 38123 Trento, Italy
²² Physikalisches Institut, University of Bern, 3012 Bern, Switzerland
²³ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
²⁴ Instituto de Astrofísica de Andalucía (CSIC), c/Glorieta de la Astronomía, 18008 Granada, Spain
²⁵ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany
²⁶ European Space Astronomy Centre (ESAC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
²⁷ Centre for Astrophysics and Planetary Science, School of Physical Sciences, The University of Kent, Canterbury CT2 7NH, UK
²⁸ Southwest Research Institute, Boulder, CO, USA
²⁹ Department of Information Engineering, University of Padova, via gradenigo 6/B, 35131 Padova, Italy
³⁰ MTA CSFK Konkoly Observatory, 1121 Budapest, Hungary

Received: 19 January 2016
Accepted: 18 April 2016

Abstract

Aims. We aim to characterize the circular depressions of comet 67P/Churyumov-Gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a Jupiter family comet (JFC).

Methods. The images from the Rosetta/OSIRIS science camera experiment are used to construct size frequency distributions of the circular depression structures on comet 67P and they are compared with those of the JFCs 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2. The orbital evolutionary histories of these comets over the past 100 000 yr are analyzed statistically and compared with each other.

Results. The global distribution of the circular depressions over the surface of 67P is charted and classified. Descriptions are given to the characteristics and cumulative size frequency distribution of the identified features. Orbital statistics of the JFCs visited by spacecraft are derived.

Conclusions. The size frequency distribution of the circular depressions is found to have a similar power law distribution to those of 9P/Tempel 1 and 81P/Wild 2. This might imply that they could have been generated by the same process. Orbital integration calculation shows that the surface erosion histories of 81P/Wild 2, and 9P/Tempel 1 could be shorter than those of 67P, 103 P/Hartley 2 and 19P/Borrelly. From this point of view, the circular depressions could be dated back to the pre-JFC phase or the transneptunian phase of these comets. The north-south asymmetry in the distribution of the circular depressions could be associated with the heterogeneous structure of the nucleus of comet 67P and/or the solar insolation history.