Introduction

A lot of extrasolar planets were found and the numbers increase, one can not find Earth-sized planets yet. Today we have only observational evidence of extrasolar planets of 7 earth masses (Gliese 876d) and larger. The size of such planets is too large for the formation of life and only a few of these planets lie in the 'Habitable Zone' (HZ). The HZ is defined as a region around a star, where the radiation for a earh-like planet is such that the planet can maintain liquid water on the surface and a stable atmosphere. Therefore we are looking for new possible dynamical configurations where a habitable planet may host life. There are four possible configurations for terrestrial like planets:

Type 1: a gas giant (GG) is very close to the central star thus a terrestrial planet (TP) could exist with a stable orbit in the HZ.
Type 2: when a GG moves far away from the central star (like Jupiter), then stable low eccentric orbits for TPs can exist inside the orbit of the giant planet.
Type 3: when a GG itself moves in the HZ, a terrestriallike satellite (like e.g. Europa in the system of Jupiter) could have a stable orbit (see also Domingos, Winter & Yokoyama 2006).
Type 4: when a GG itself moves in the HZ, a Trojan-like (short introduction about Trojan asteroids) TP may move in a stable orbit around the Lagrangian equilibrium points L4 or L5.

Designed by
Richard Schwarz
© by Department of Astronomy, Eötvös University Budapest; and
Institute for Astronomy, University of Vienna