Shape model, reference system definition, and cartographic mapping standards for comet 67P/Churyumov-Gerasimenko – Stereo-photogrammetric analysis of Rosetta/OSIRIS image data^⋆

¹ German Aerospace Center (DLR), Institute of Planetary Research, 12489 Berlin, Germany
e-mail: Frank.Preusker@dlr.de
² Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France
³ Instituto de Astrofisica de Andalucia (CSIC), c/ Glorieta de la Astronomìa s/n, 18008 Granada, Spain
⁴ University of Maryland, Department of Astronomy, College Park, MD 20742-2421, USA
⁵ Physikalisches Institut der Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland
⁶ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany
⁷ University of Padova, Department of Physics and Astronomy, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁸ Centro de Astrobiología, CSIC-INTA, Torrejón de Ardoz, 28850 Madrid, Spain
⁹ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
¹⁰ Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
¹¹ Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
¹² PAS Space Reserch Center, Bartycka 18A, 00716 Warszawa, Poland
¹³ Institut für Geophysik und extraterrestrische Physik (IGEP), Technische Universität 31 Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
¹⁴ LESIA, Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon Principal Cedex, France
¹⁵ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁶ Center of Studies and Activities for Space (CISAS) “G. Colombo”, University of Padova, via Venezia 15, 35131 Padova, Italy
¹⁷ INAF–Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
¹⁸ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁹ Department of Industrial Engineering – University of Padova, via Venezia 1, 35131 Padova, Italy
²⁰ UNITN, Universitá di Trento, via Mesiano 77, 38100 Trento, Italy
²¹ Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris Cedex 13, France
²² INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
²³ Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
²⁴ ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
²⁵ Institut für Datentechnik und Kommunikationsnetze, Hans-Sommer-Str. 66, 38106 Braunschweig, Germany
²⁶ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy

Received: 17 April 2015
Accepted: 2 July 2015

Abstract

We analyzed more than 200 OSIRIS NAC images with a pixel scale of 0.9−2.4 m/pixel of comet 67P/Churyumov-Gerasimenko (67P) that have been acquired from onboard the Rosetta spacecraft in August and September 2014 using stereo-photogrammetric methods (SPG). We derived improved spacecraft position and pointing data for the OSIRIS images and a high-resolution shape model that consists of about 16 million facets (2 m horizontal sampling) and a typical vertical accuracy at the decimeter scale. From this model, we derive a volume for the northern hemisphere of 9.35 km³ ± 0.1 km³. With the assumption of a homogeneous density distribution and taking into account the current uncertainty of the position of the comet’s center-of-mass, we extrapolated this value to an overall volume of18.7 km³± 1.2 km³, and, with a current best estimate of 1.0 × 10¹³ kg for the mass, we derive a bulk density of 535 kg/m³± 35 kg/m³. Furthermore, we used SPG methods to analyze the rotational elements of 67P. The rotational period for August and September 2014 was determined to be 12.4041 ± 0.0004 h. For the orientation of the rotational axis (z-axis of the body-fixed reference frame) we derived a precession model with a half-cone angle of 0.14°, a cone center position at 69.54°/64.11° (RA/Dec J2000 equatorial coordinates), and a precession period of 10.7 days. For the definition of zero longitude (x-axis orientation), we finally selected the boulder-like Cheops feature on the big lobe of 67P and fixed its spherical coordinates to 142.35° right-hand-rule eastern longitude and –0.28° latitude. This completes the definition of the new Cheops reference frame for 67P. Finally, we defined cartographic mapping standards for common use and combined analyses of scientific results that have been obtained not only within the OSIRIS team, but also within other groups of the Rosetta mission.