The global shape, density and rotation of Comet 67P/Churyumov-Gerasimenko from preperihelion Rosetta/OSIRIS observations - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Icarus Year : 2016

The global shape, density and rotation of Comet 67P/Churyumov-Gerasimenko from preperihelion Rosetta/OSIRIS observations

1 LAM - Laboratoire d'Astrophysique de Marseille
2 PSI - Planetary Science Institute [Tucson]
3 DLR Institute of Planetary Research
4 Astronomical Institute of Charles University
5 IAA - Instituto de Astrofísica de Andalucía
6 KinetX Aerospace Inc.
7 JPL - Jet Propulsion Laboratory
8 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
9 SSERVI - Solar System Exploration Research Virtual Institute
10 UMass Amherst - University of Massachusetts [Amherst]
11 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
12 Department of Astronomy [College Park]
13 Dipartimento di Fisica e Astronomia "Galileo Galilei"
14 CAB - Centro de Astrobiologia [Madrid]
15 ISSI - International Space Science Institute [Bern]
16 ESTEC - European Space Research and Technology Centre
17 Department of Physics and Astronomy [Uppsala]
18 CBK - Space Research Centre of Polish Academy of Sciences
19 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
21 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
22 OAPD - INAF - Osservatorio Astronomico di Padova
23 IFN - CNR Institute for Photonics and Nanotechnologies
24 Department of Industrial Engineering [Padova]
25 University of Trento [Trento]
26 OAT - INAF - Osservatorio Astronomico di Trieste
27 Institute of Space Science [Taiwan]
28 Operations Department (ESAC)
29 DEI - Department of Information Engineering [Padova]
30 Physikalisches Institut [Bern]
31 RSSD - Research and Scientific Support Department, ESTEC
Laurent Jorda
Pedro J. Gutiérrez
  • Function : Author
  • PersonId : 880386
C. Jackman
Jean-Loup Bertaux
  • Function : Author
  • PersonId : 914210
Nicolas Thomas


The Rosetta spacecraft reached Comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) in August 2014 at an heliocentric distance of 3.6 a.u. and was then put in orbit around its nucleus to perform detailed observations. Among the collected data are the images acquired by the OSIRIS instrument up to the perihelion passage of the comet in August 2015, which allowed us to map the entire nucleus surface at high-resolution in the visible. Stereophotoclinometry methods have been used to reconstruct a global high-resolution shape model and to monitor its rotational parameters using data collected up to perihelion. The nucleus has a conspicuous bilobate shape with overall dimensions along its principal axes of (4.34 ± 0.02) × (2.60 ± 0.02) × (2.12 ± 0.06) km. The best-fit ellipsoid dimensions of the individual lobes along their principal axes of inertia are found to be 4.10 × 3.52 × 1.63 km and 2.50 × 2.14 × 1.64 km. Their volume amounts to 66% and 27% of the total volume of the nucleus. The two lobes are connected by a “neck” whose volume has been estimated to represent ∼7% of the total volume of the comet. Combining the derived volume of 18.8 ± 0.3 km3 with the mass of 9.982 ± 0.003 × 1012 kg determined by the Rosetta/RSI experiment, we obtained a bulk density of the nucleus of 532±7 kg m-3. Together with the companion value of 535±35 kg m deduced from the stereophotogrammetry shape model of the nucleus (Preusker et al. [2015] Astron. Astrophys. 583, A33), these constitute the first reliable and most accurate determination of the density of a cometary nucleus to date. The calculated porosity is quite large, ranging approximately from 70% to 75% depending upon the assumed density of the dust grains and the dust-to-ice mass ratio. The nature of the porosity, either micro or macro or both, remains unconstrained. The coordinates of the center of gravity are not compatible with a uniform nucleus density. The direction of the offset between the center of gravity and the center of figure suggests that the big lobe has a slightly higher bulk density compared to the small one. the center of mass position cannot be explained by different, but homogenous densities in the two lobes. The initial rotational period of 12.4041 ± 0.0001 h of the nucleus persisted until October 2014. It then slightly increased to a maximum of 12.4304 h reached on 19 May 2015 and finally dropped to 12.305 h just before perihelion on August 10, 2015. A periodogram analysis of the (RA, Dec) direction of the Z-axis of the comet obtained in parallel with the shape reconstruction exhibits a highly significant minima at 11.5 ± 0.5 day clearly indicating an excited rotational state with an amplitude of 0.15 ± 0.03°.
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Dates and versions

insu-01322943 , version 1 (29-05-2016)



Laurent Jorda, R. Gaskell, C. Capanna, S. Hviid, Philippe Lamy, et al.. The global shape, density and rotation of Comet 67P/Churyumov-Gerasimenko from preperihelion Rosetta/OSIRIS observations. Icarus, 2016, 277, pp.257-278. ⟨10.1016/j.icarus.2016.05.002⟩. ⟨insu-01322943⟩
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