The outer solar system may have a shorter future than expected

For decades, the outer solar system was granted an absurdly long lease on life. Jupiter, Saturn, Uranus and Neptune were expected to keep their orbits for about a quintillion years, a figure so large it practically belongs in a museum of cosmic overconfidence. A new study from the California Institute of Technology now trims that expectation to something rather less serene: roughly a billion years after the Sun becomes a white dwarf, the giant planets may start to lose their stability.

That is still a long wait, of course. The Sun itself has around five billion years left before it swells into a red giant, at which point Earth, Venus and Mercury are expected to be consumed. Mars, according to earlier studies, should remain just far enough away to survive the engulfment. The outer planets were long thought to endure that phase and then drift on, their orbits widening as the Sun shed mass, until passing stars finally disturbed them tens of billions of years later.

The new paper says that tidy story is too tidy. Once the Sun becomes a white dwarf, it is expected to rapidly cool and shrink to about half its current size, but the loss of mass may not happen in a smooth, predictable way. The researchers instead describe violent, random ejections of material, which they call stochastic kicks, and argue that these could throw the giant planets into disorder much sooner than anyone had assumed.

To reach that conclusion, the team used high-performance supercomputers and hundreds of advanced N-body simulations. They built a virtual solar system containing the Sun, Jupiter, Saturn, Uranus and Neptune, then tracked their velocities and positions over billions of years. The difference in this year’s analysis was the way the Sun’s dying mass loss was modelled: as random, episodic bursts, tested across hundreds of model iterations before the researchers drew their conclusion.

The study, published in The Astrophysical Journal Letters under the title Terminal Instability of the Solar System Triggered by Stochastic Solar Mass Loss, does not mean the outer planets are about to fall apart any time soon. It does suggest, however, that even the solar system’s supposedly safest neighbourhood may be less permanent than older estimates implied. Nature, as usual, has no interest in preserving our neat timelines.

Written by Christiane Hofreiter christiane.hofreiter@alpineweekly.com