The Planetary System

Abstract

In this chapter we give an overview of the properties of our planetary system — both those related to its dynamical structure, namely the orbital and rotational motions of the constituent bodies, and those connected with their physical nature (e.g., size, composition, the presence of an atmosphere and/or of a solid surface). As discussed in the Introduction, our principal aim is not descriptive, but rather to provide insight into the main physical principles and processes; thus some data will be presented in the form of tables and figures with synthetic captions only. In the case of minor bodies, we mainly focus on presenting orbital clusterings and their interrelations; often the individual orbits in these populations are not stable throughout the age of the solar system, and the problem of sustaining the entire family by adequately efficient sources is fundamental. In this context we note that the formation of orbital structures in the inner solar system, such as the main asteroid belt, is coarsely understood. The unsolved issues include how the unstable population of planet-crossing objects (e.g., the near-Earth objects) is sustained over a long period of time. A major unanswered question is how structures in the outer solar system, such as the Kuiper belt and related populations of objects, have been formed. This problem is also intimately linked to the formation of the giant planets, a very attractive topic due to the discovery of extrasolar planetary systems. Significant contributions to the understanding of the highly unstable cometary populations have been made in the last decade, yet some problems remain unsolved (such as the appearance of dormant comets in the outer asteroid belt and among the near-Earth object population).