From planetesimal discs in wide binaries to the outer-remnants of planet formation : variations on the dynamics of small bodies with big companions -

Abstract

This thesis is divided into two interrelated parts, touching on the dynamical evolution of ensembles of small bodies whose motion is strongly affected by massive perturbers (in addition to their own self-gravity). The setting evolves from the early stages of planet formation in wide binaries, to observed features in the remnant icy bodies in the outer confines of our Solar System. The first part of the thesis is dedicated to studying semi-analytically the secular dynamics of planetesimals - the building blocks of planets - embedded in an eccentric gaseous protoplanetary disc and to explore the physical conditions for their growth around one of the components of an eccentric S-type binary star system. We take into consideration several essential physical ingredients relevant to the problem: (1) perturbations due to the stellar companion, (2) gravitational effects of an eccentric disc, (3) gas drag-induced dissipation, (4) rigid disc precession and (5) dissipation of the gaseous component from the disc itself. We perform extensive study to unveil the dynamical effects of each of the perturbations considered. We first analyze the resultant dynamics in the presence of the combined gravitational effects of the disc and the binary companion. We find that the disc self-gravity, which has been neglected so far in almost all numerical and analytical studies, is a vital component and that it represents an important ingredient in developing a complete understanding of planetesimal dynamics. Furthermore, including all sources of perturbations, we demonstrate that an evolving disc which loses its mass with time - an inevitable phenomenon - can be problematic for planet formation. Indeed, our results demonstrate that in such a scenario planetesimals can be emplaced on high eccentricity orbits, thus rendering collisions among them destructive rather than accretion-friendly. Thus, our results show that in-situ planet formation seems difficult within our framework of study. Finally, we discuss some dynamical pathways - inferre