Abstract
We have investigated the evolution of the structure of the Oort cloud and the distribution of "new comets" from the Oort cloud due to the galactic tide. Oort cloud comets are believed to be planetesimals, which are scattered by planets. We considered the effect of the vertical component of the tidal force from the galactic disk on the structure of the Oort cloud. Due to the galactic tide, the eccentricity and inclination of some planetesimals conversely oscillate a great deal. This is an effective mechanism to form the Oort cloud and to bring back comets in the Oort cloud to the planetary region as new comets. We examined the effect by applying the analytical solutions to the orbital evolution of planetesimals.We found that due to the galactic tide, planetesimals with the semimajor axes >~1,000 AU raise the perihelion distances outside the planetary region in 4.5 Gyr. We also found that the galactic tide alone can not realize the isotropic distribution of inclination of the Oort cloud comets and the new comets, which is expected from the observation of long period comets.
