Details

Autor(en) / Beteiligte

• Jorda, L.
• Gaskell, R.
• Capanna, C.
• Hviid, S.
• Lamy, P.
• Ďurech, J.
• Faury, G.
• Groussin, O.
• Gutiérrez, P.
• Jackman, C.
• Keihm, S.J.
• Keller, H.U.
• Knollenberg, J.
• Kührt, E.
• Marchi, S.
• Mottola, S.
• Palmer, E.
• Schloerb, F.P.
• Sierks, H.
• Vincent, J.-B.
• A’Hearn, M.F.
• Barbieri, C.
• Rodrigo, R.
• Koschny, D.
• Rickman, H.
• Barucci, M.A.
• Bertaux, J.L.
• Bertini, I.
• Cremonese, G.
• Da Deppo, V.
• Davidsson, B.
• Debei, S.
• De Cecco, M.
• Fornasier, S.
• Fulle, M.
• Güttler, C.
• Ip, W.-H.
• Kramm, J.R.
• Küppers, M.
• Lara, L.M.
• Lazzarin, M.
• Lopez Moreno, J.J.
• Marzari, F.
• Naletto, G.
• Oklay, N.
• Thomas, N.
• Tubiana, C.
• Wenzel, K.-P.

Titel

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

Ist Teil von

• Icarus (New York, N.Y. 1962), 2016-10, Vol.277, p.257-278

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2016

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• •We derived a global 3D shape model and the rotational parameters of comet 67P/C-G from high-resolution visible images collected aboard the Rosetta spacecraft.•Using this model, we could calculate accurate nucleus parameters including a volume of 18.8 ± 0.3 km3 and a density of 532 ± 7 kg m−3.•We could also retrieve the shape and the geometry of the two lobes using computer graphics tools.•A slight excitation of the spin state was detected, with a precession period of 11.5 ± 0.5 day.•The coordinates of the spin axis indicates a slight inhomogeneity of the density distribution. 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±7kgm−3. Together with the companion value of 535±35kgm−3 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°.