Dynamical Instabilities and the Formation of Extrasolar Planetary Systems

TLDR

The presence of a dominant massive planet such as Jupiter may be uncommon in other planetary systems, and in systems with two Jupiter‑like planets dynamical instabilities can arise. Simulations show that such instabilities often eject one planet, leaving the survivor in a smaller, eccentric orbit that can circularize to a few‑day period via tidal dissipation, potentially explaining the observed close‑in Jupiter‑mass planets.

Abstract

The existence of a dominant massive planet, Jupiter, in our solar system, although perhaps essential for long-term dynamical stability and the development of life, may not be typical of planetary systems that form around other stars. In a system containing two Jupiter-like planets, the possibility exists that a dynamical instability will develop. Computer simulations suggest that in many cases this instability leads to the ejection of one planet while the other is left in a smaller, eccentric orbit. In extreme cases, the eccentric orbit has a small enough periastron distance that it may circularize at an orbital period as short as a few days through tidal dissipation. This may explain the recently detected Jupiter-mass planets in very tight circular orbits and wider eccentric orbits around nearby stars.