Universe Today – Earth’s place in the “Goldilocks” zone of our solar system may be the result of the expulsion of a fifth giant planet from our solar system during its first 600 million years, according to a recent journal publication.
Recent studies of solar system formation 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. Here we performed N-body integrations of the scattering phase between giant planets in an attempt to determine which initial states are plausible. We 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.
Animation showing the evolution of the planetary system from 20 million years before the ejection to 30 million years after. Five initial planets are shown by red circles, small bodies are in green. After the fifth planet is ejected, the remaining four planets stabilize after a while, and looks like the outer solar system in the end, with giant planets at 5, 10, 20 and 30 astronomical units. Click image to view animation. Image Credit: Southwest Research Institute
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