Abstract
Comets are classified into two main families according to their orbital properties : comets of the Jupiter family and comets with an isotropic distribution. The former come from the Kuiper belt, more precisely from its sub-component known as the dispersed disk. The latter come from a reservoir at the very edge of the Solar System, the Oort cloud. The mechanisms that transport comets from their sources to the inner Solar System will be detailed, as will the origins of these two reservoirs. We will also address the scientific debate surrounding the possible existence of a ninth planet in the Solar System.
