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New research has found that the existence of a fifth giant planet that was ejected could help explain the irregular moons of Jupiter and Uranus.
A new study that has not yet been peer-reviewed raises new questions about one of the most popular theories about the evolution of the Solar System.
which is available for pre-publication viewing on arXiv, suggests that the violent planetary reorganization, believed to have occurred billions of years ago, could be difficult to reconcile with the survival of a few moons of Jupiter and Uranus.
The investigation revisits the so-called Nice modelan important theory developed in 2005 that proposes that giant planets did not form in their current positions. Instead, it is believed that Jupiter, Saturn, Uranus and Neptune migrated through the Solar System after a period of orbital instability. Some versions of the model even suggest that a fifth giant planet may have been ejected into interstellar space.
The Nice Model has long been considered one of the best explanations for several intriguing features of the Solar System, including the current orbits of the giant planets, the existence of Trojan asteroids that share Jupiter’s orbit, and the irregular moons that orbit some outer planets. However, according to , the new simulations indicate that such a chaotic period may have had a significant cost.
The researchers tested 122 plausible scenarios of the early evolution of the Solar System, including models with an additional ice giant planet. They focused on whether the Jupiter and Uranus satellite systems could have survived the gravitational upheaval predicted by the Nice Model.
The results were surprising. According to the study, the probability of survival of the moon systems of Jupiter and Uranus was generally less than 15%.
“We identified only one case in which the large satellites of Uranus and Jupiter consistently survived the same instability,” the researchers wrote.
The findings suggest that the planetary encounters required by the Nice Model often destabilize or destroy the moons that orbit giant planets. Simulations that successfully preserved Jupiter’s satellites often failed to protect Uranus’s system of moons, while scenarios favorable to Uranus tended to be less successful for Jupiter.
The researchers found that Jupiter’s moons were more likely to survive in models that contained two additional smaller ice giants, while Uranus’ satellites fared better when only one additional larger planet was involved. Any close encounter between Uranus and another ice giant, however, would take almost invariably to the destruction of its moon system.
The study does not reject the Nice Model completely, but suggests it may need refinement. Scientists propose several alternative explanations, including the possibility that Uranus has gone through multiple rupture periods of their satellites or having, in some way, avoided close encounters with other giant planets during the instability phase.
“While it is certainly possible that all four early regular satellite systems in the outer solar system were unaffected by planetary encounters, our results strongly suggest that this is not the case“, concluded the investigators.
