Abstract

In a planetary system where planets are well spaced and interact only through their secular (i.e., non-resonant) perturbations, there exists a nonlinear instability that leads to chaotic behaviour. Some planets (the most unstable ones) may gradually obtain very large values of eccentricities and/or inclinations. We elucidate the condition under which this occurs.

When a most unstable planet is removed from the system, either through close encounter with another planet, or through close encounter with the star (where tidal effects might kick in), the remaining planetary system becomes increasingly more stable. This, as opposed to planet-planet scattering, may explain the stable architecture of the observed systems.

In the case of the most unstable planet moving in toward close encounter with the star, its pericentre dipping may be tidally stalled around a few stellar radii. When these orbits are tidally circularized, we obtain hot jupiters (or hot neptunes). This scenario for hot jupiter formation explains a variety of observed phenomena, including correlations between planet mass and semi-major axis, coplanarity of planet orbit and stellar spin, as well as the paucity of second planets around hot jupiters.