Orbital evolution of three asteroids for 100 Myr in semi-major axis and eccentricity. Each starts from the conveyor belt (to the top left) until it circularizes. These asteroids are launched into the conveyor belt by a giant planet. This process is illustrated in Fig. 5. Once the Galactic tidal field starts to dominate the orbital evolution of the asteroids (to the right of the red dashed curve), it detaches them from the influence of the inner planets. The Galactic tidal field subsequently drives the eccentricity evolution of the asteroid until it circularizes. The timescale of the circularization process is illustrated with the color bar. Asteroids further in the Oort cloud are more strongly affected by the Galactic tidal field, and therefore have a shorter circularization timescale. Not all asteroids circularize to the low eccentricities of the three examples presented here. The eventual eccentricity distribution of the Oort cloud objects is presented inFig. 8. The vertical dotted curve to the right indicates the Hill radius of the Solar System in the Galactic potential.