Oort cloud formation at various Galactic distances

Abstract

In this study we present the results from numerical simulations of the formation of the Oort comet cloud where we positioned the Sun in various parts of the disc of the Galaxy, starting at 2 kpc up to 20 kpc from the Galactic centre. All simulations were run for 4 Gyr. We report that the final trapping efficiency of comets in the Oort cloud is approximately 4% and is almost independent of the solar distance from the Galactic centre. This efficiency is not enough to explain the flux of long-period comets and be consistent with the mass of the protoplanetary disc. In addition, the population ratio between the Oort clouds and their corresponding scattered discs is at least two orders of magnitude lower than observed today. Solar migration from the inner regions of the Galaxy-where the initial trapping efficiency is higher-to farther regions-where the retention is higher-does not add enough of an effect to increase the efficiency to the necessary value of approximately 20%, so that other mechanisms for forming the Oort cloud need to be investigated. © ESO 2010.