67P/Churyumov-Gerasimenko - potential target for the Rosetta mission

Abstract

An influence of the non-gravitational effects on the motion of short-period comet 67P/Churyumov-Gerasimenko is investigated. It was found that the normal component of the non-gravitational force exceeds the transverse one and a model of the motion including A_1, A_2, A_3 better fits the observations than model neglecting A_3. Assuming asymmetry in g(r) with respect to the perihelion the large value of displacement \tau was derived (about 34 days), and very small negative value of transverse component A_2 was obtained. The models of rotating non-spherical nucleus also suggest the large shift of light curve with respect to perihelion (\tau greater than 30 days). The forced precession model of 67P with \tau = 34 days gives a prolate spheroidal shape of the rotating nucleus with axial ratio R_b/R_a = 1.16, rotational period to equatorial radius P_{rot}/R_a = 4.6\pm 1.4 hrs/km, and torque factor f_{tor}=3\cdot 10^5 day/AU. The much larger \tau = 54 days gives distinctly prolate shape of nucleus with axial ratio R_b/R_a = 1.71. The orientation of spin axis of the nucleus and its evolution are presented. The past and the future dynamical evolution of comet 67P is also widely discussed.