The stability of ultra-compact planetary systems

Aims. We investigate the dynamical stability of compact planetary systems in the CoRoT discovery space, i.e., with orbital periods of less than 50 days, including a detailed study of the stability of systems, which are spaced according to Hill’s criteria. Methods. The innermost fictitious planet was placed close to the Roche limit from the star (MStar = 1 MSun) and all other fictitious planets are lined up according to Hill’s criteria up to a distance of 0.26 AU, which corresponds to a 50 day period for a Sun-massed star. For the masses of the fictitious planets, we chose a range of 0.33–17 mEarth, where in each simulation all fictitious planets have the same mass. Additionally, we tested the influence of both the semi-major axis of the innermost planet and of the number of planets. In a next step we also included a gas giant in our calculations, which perturbs the inner ones and investigated their stability. Results. With numerous integrations of many different configurations we could show that long-time stable motion is possible for up to 10 planets with 17 mEarth within a distance of 0.26 AU. Further investigations show that the fictitious planets remain stable under certain circumstances even if a close-in gas giant is present.

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