Evidence for a precession of the nucleus of comet 67P/C-G from ROSETTA/OSIRIS images
Résumé
The retrieval of the rotational parameters of comet 67P/C-G is part of the shape reconstruction process conducted from data collected by the OSIRIS imaging system aboard ROSETTA. Among other parameters, this includes the reconstruction of the (RA,Dec) direction of the Z axis of the body-fixed frame and that of the angular momentum vector. The stereophotogrammetric solution (Preusker et al., A&A 2015, in press) obtained in Aug-Sep 2014 already showed evidence for a complex rotation of comet 67P/C-G. A subsequent analysis of the rotational data obtained using the stereophotoclinometry method (Gaskell et al., MP&S 43, 1049, 2008) up to April 2015 also revealed a precession with a likelihood greater than 99.99 %. The amplitude and period of the (RA,Dec) variations measured with both methods are fully compatible.We propose an interpretation of the measured period as a combination of torque free motions: a rotation combined with a precession of small amplitude. The modeling of this motion has implications on the value of the moments of inertia, from which it is possible to constrain the internal density distribution of comet 67P/C-G.