On the Stability of Extra-Solar Planetary Systems

Abstract

. Since the discovery of the ?rst extra-solar planet near a Sun-like star (i.e., 51Peg b) numerous planets outside the solar system have been discovered during the last century (by October 2006, 168 extra-solar planetary systems are known). For dynamical studies the 20 multi-planet systems and the 21 binary systems that host one or more planets are important to be examined, since gravitational interactions between the celestial bodies restrict the stable planetary motion to certain regions in the phase space of such a system. Besides the investigation of these systems, stability studies of hypothetical terrestrial-like planets in all systems are of special interest.

In this chapter we give a short overview about the discovered extra-solar planetary systems and the di?erent detection methods. Then we discuss the multi-planet systems according to a classi?cation of Ferraz-Mello. For the planetary motion in binary systems we introduce the three types of motion and show the results of general stability studies thereto on the one hand and the application of these studies to real binary systems on the other hand. Furthermore, we discuss the in?uence of the perturbing star (i.e., secondary) on the planetary motion in brief.

In the last part of this chapter we concentrate on the stability of Earth-like planets moving in the so-called habitable zone. This study is important, especially with regard to current (CoRoT) and forthcoming space missions (like e.g., Kepler, Darwin, TPF) that try to ?nd a planet—similar to our Earth—where complex life could have developed. Since we know that the development of a biosphere and the further evolution to intelligent life-form is a process on a long timescale, the longterm stability of such a planet is an important and necessary condition for the habitability of a planet.