New simulations suggest giant planets may become unstable and be ejected from their orbits much earlier than previously thought, challenging existing estimates.
New simulations on planetary stability
New simulations suggest that the giant planets in the outer Solar System could become unstable and be ejected from their orbits much earlier than previously thought. These findings challenge earlier estimates that the intrinsic dynamical lifetime of the outer Solar System was approximately 10¹⁸ years.Sun's future as a white dwarf
According to the simulations, instabilities could arise as early as a billion years following the Sun's transformation into a white dwarf. The Sun is expected to begin its final phase of existence in about 5 billion years, during which it will exhaust its thermonuclear fuel and transform into a red giant.Inner planets' stability
Models predict that the orbits of the inner planets—Mercury, Venus, Earth, and Mars—have little chance of being destabilized during the red giant phase and subsequent stages of the Sun's evolution. Simulations of the Solar System's evolution over five billion years indicate that Mercury's orbit has approximately a 1 percent probability of destabilization before the Sun leaves the main sequence.Uncertain future for giant planets
The future of the giant planets—Jupiter, Saturn, Uranus, and Neptune—remains uncertain. Some models suggest that these planets could maintain stable orbits even several billion years after the Sun has ejected its outer envelope. Previous estimates placed the intrinsic dynamical lifetime of the outer Solar System around 10¹⁸ years, while other studies estimated that external perturbations could disrupt the orbits of the giant planets after several tens of billions of years.New simulations from Caltech and University of Michigan
Recent simulations conducted by a team from the California Institute of Technology (Caltech) and the University of Michigan suggest that instabilities could arise much earlier than previously thought, due to the loss of mass by the Sun and the perturbations it causes. The researchers note that previous estimates relied on the hypothesis of a continuous loss of solar mass.Testing the hypothesis
To test their hypothesis, the team combined a detailed stellar evolution model with algorithms designed to evaluate the probabilities of orbital changes for Jupiter, Saturn, Uranus, and Neptune as the Sun loses mass through sporadic ejections of matter. The researchers explored 672 scenarios of solar mass ejection, varying the magnitude of mass loss episodes in their simulations.Results of the simulations
In one of the scenarios involving strong mass ejections, 46 of the 48 simulated systems, or about 96 percent, become unstable within the three billion years following the formation of the white dwarf. In the same scenario, about 40 percent of the simulated systems experience strong perturbations or violent orbital dispersion before even the formation of the white dwarf.Diverse outcomes of simulations
In other simulations, about 90 percent of the simulated systems become unstable in less than three billion years. Some scenarios lead to the ejection of Jupiter and Saturn out of the Solar System, while Uranus and Neptune exchange their orbits. Conversely, more moderate mass ejections sometimes cause certain pairs of planets to enter mean-motion resonances.Implications for the Solar System's future
The researchers explain that any architectural rearrangement is not necessarily destructive, and the random walk presents a subtler side effect: occasional capture into mean-motion resonances, which are impossible to reach in the adiabatic limit. Overall, the modeling suggests that the dynamical lifetime of the outer Solar System could be reduced from approximately 10¹⁸ years to a billion years after the formation of the white dwarf. These results, however, depend on the mass loss scenarios considered and do not mean that all giant planets will necessarily be ejected or destabilized within this timeframe.
