The recent dynamical history of comet 67P/Churyumov-Gerasimenko

This paper presents the past evolution of the orbital elements of comet 67P/Churyumov-Gerasimenko, target of the Rosetta spacecraft. The gravitational orbit of the comet is affected by the sublimation of ice from the nucleus that triggers non-gravitational forces. The comet also experienced several close encounters with Jupiter, especially notable were those in 1959 and 1923 (less than 1 AU). These perturbations cause the chaoticity of the comet orbit at short time scale. The goal of this paper is to have a precise idea of the comet's recent dynamical history. This is done by studying the mean trends of the orbital elements of the comet and also by characterising its chaotic motion with the fast Lyapunov indicator. To compute these mean trends, two sets (considering or not the non-gravitational forces) of 1000 clone orbits of the comet were considered. This paper shows that the last close encounter with Jupiter on February 4, 1959, drastically modified the orbital elements of the comet (especially the perihelion distance: from more than 2.7 AU before the encounter to 1.3 AU after the encounter). The motion of the comet is also shown to be chaotic before the close encounter with Jupiter on October 2, 1923. The mean trends of the orbital elements of the comet are also presented in this paper (for two time scales: 270 years in the past and 10 000 years in the past).