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

F. Preusker (1) , F. Scholten (1) , K.-D. Matz (1) , T. Roatsch (1) , K. Willner (1) , S. F. Hviid (1) , J. Knollenberg (1) , L. Jorda (2) , Pedro J. Gutiérrez (3) , Ekkehard Kührt (1) , S. Mottola (1) , Michael F. A'Hearn (4) , Nicolas Thomas (5) , Holger Sierks (6) , C. Barbieri (7) , P. Lamy (2) , R. Rodrigo (8, 9) , Detlef Koschny (10) , H. Rickman (11, 12) , Horst U. Keller (13) , J. Agarwal (6) , M.A. Barucci (14) , Jean-Loup Bertaux (15) , I. Bertini (16) , Gabriele Cremonese (17) , Vania da Deppo (18) , Björn Davidsson (12) , S. Debei (19) , M. de Cecco (20) , S. Fornasier (14, 21) , M. Fulle (22) , Olivier Groussin (2) , Carsten Güttler (6) , W.-H. Ip (23) , J. R. Kramm (6) , Michael Küppers (24) , L. M. Lara (3) , M. Lazzarin (7) , José J. Lopez Moreno (3) , F. Marzari (25) , H. Michalik (26) , G. Naletto (18, 19, 16) , N. Oklay (6) , C. Tubiana (6) , J.-B. Vincent (6)

1 DLR Institute of Planetary Research
2 LAM - Laboratoire d'Astrophysique de Marseille
3 IAA - Instituto de Astrofísica de Andalucía
4 Department of Astronomy [College Park]
5 Physikalisches Institut [Bern]
6 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
7 Dipartimento di Fisica e Astronomia "Galileo Galilei"
8 ISSI - International Space Science Institute [Bern]
9 CAB - Centro de Astrobiologia [Madrid]
10 RSSD - Research and Scientific Support Department, ESTEC
11 CBK - Space Research Centre of Polish Academy of Sciences
12 Department of Physics and Astronomy [Uppsala]
13 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
14 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
15 PLANETO - LATMOS
16 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
17 OAPD - INAF - Osservatorio Astronomico di Padova
18 IFN - CNR Institute for Photonics and Nanotechnologies
19 Department of Industrial Engineering [Padova]
20 UNITN - Università degli Studi di Trento = University of Trento
21 UPD7 - Université Paris Diderot - Paris 7
22 OAT - INAF - Osservatorio Astronomico di Trieste
23 IANCU - Institute of Astronomy [Taiwan]
24 Operations Department (ESAC)
25 Dipartimento di Fisica
26 Institut für Datentechnik und Kommunikationsnetze

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 of 18.7 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.

Mots clés: Reference systems; Comets

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]

F. Preusker, F. Scholten, K.-D. Matz, T. Roatsch, K. Willner, et al.. Shape model, reference system definition, and cartographic mapping standards for comet 67P/Churyumov-Gerasimenko. Stereo-photogrammetric analysis of Rosetta/OSIRIS image data. Astronomy and Astrophysics - A&A, 2015, 583, A33 (19 p.). ⟨10.1051/0004-6361/201526349⟩. ⟨insu-01202229⟩