The secular evolution of the Kuiper belt after a close stellar encounter

We show the effects of the perturbation caused by a passing by star on the Kuiper belt objects (KBOs) of our Solar system. The dynamics of the Kuiper belt (KB) is followed by direct N-body simulations. The sampling of the KB has been done with N up to 131 062, setting the KBOs on initially nearly circular orbits distributed in a ring of surface density Sigma similar to r(-2). This modellization allowed us to investigate the secular evolution of the KB upon the encounter with the perturbing star. Actually, the encounter itself usually leads towards eccentricity and inclination distributions similar to observed ones, but tends also to excite the low-eccentricity population (e less than or similar to 0.1 around a similar to 40 au from the Sun), depleting this region of low eccentricities. The following long-term evolution shows a 'cooling' of the eccentricities repopulating the low-eccentricity area. In dependence on the assumed KBO mass spectrum and sampled number of bodies, this repopulation takes place in a time that goes from 0.5 to 100 Myr. Due to the unavoidable limitation in the number of objects in our long-term simulations (N <= 16 384), we could not consider a detailed KBO mass spectrum, accounting for low-mass objects, thus our present simulations are not reliable in constraining correlations among inclination distribution of the KBOs and other properties, such as their size distribution. However, our high-precision long-term simulations are a starting point for future larger studies on massively parallel computational platforms which will provide a deeper investigation of the secular evolution (similar to 100 Myr) of the KB over its whole mass spectrum.