Studies of a large number of exoplanetary systems indicate that planets usually forms as gasbubbles, that migrates inward as they collapse. New simulations of the creation of our own Solar-system under this assumption, shows that we initially most likely had a fifth giant gas-planets, that was thrown out by Jupiter

The new studies of our Solar-system formation under this assumption suggest that the solar system's giant planets formed and migrated in the protoplanetary disk to reach resonant orbits with all planets inside 15 AU from the Sun.

After the gas disk's dispersal, Uranus and Neptune were likely scattered by gas giants, and approached their current orbits while dispersing the transplanetary disk of planetesimals, whose remains survived to this time in the region known as the Kuiper belt.

The researchers performed N-body integrations of the scattering phase between giant planets in an attempt to determine which initial states is most plausible. And they found that the dynamical simulations starting with a resonant system of four giant planets have a low success rate in matching the present orbits of giant planets, and various other constraints (e.g., survival of the terrestrial planets). The dynamical evolution is typically too violent, if Jupiter and Saturn start in the 3:2 resonance, and leads to final systems with fewer than four planets. Several initial states stand out in that they show a relatively large likelihood of success in matching the constraints.

Some of the statistically best results were obtained when assuming that the solar system initially had five giant planets and one ice giant, with the mass comparable to that of Uranus and Neptune, was ejected to interstellar space by Jupiter. This possibility appears to be conceivable in view of the recent discovery of a large number free-floating planets in interstellar space, which indicates that planet ejection should be common.

Our current Solarsystem

Source: arXiv