Dying Sun could break up the outer solar system billions of years sooner than thought

The outer planets of our solar system may be thrown into chaos about a billion years after the Sun dies, not the near-endless time astronomers had assumed, according to a new study by Konstantin Batygin, Jim Fuller and Fred C. Adams published in The Astrophysical Journal Letters and posted as a preprint on arXiv. Euronews reported that the work comes from researchers at Caltech in the United States.

None of this touches anyone alive: the Sun has roughly five billion years left before it swells into a red giant, Euronews noted. But the result rewrites one of the oldest questions in astronomy, how long the planets' orbits stay stable.

The old answer and the new one

Why the dying Sun matters

Earlier models treated the Sun's death as smooth: as a red giant it slowly sheds its outer layers, gravity weakens, and Jupiter, Saturn, Uranus and Neptune drift calmly outward. The authors argue it is not that tidy. White dwarfs, the dense cores dying stars leave behind, are seen moving with a recoil that suggests their mass was thrown off unevenly. The team modelled that as a series of separate, randomly aimed ejections, each giving the Sun a small kick.

Each kick nudges the planets' orbits, and over many kicks those orbits wander in a random walk. In the team's computer runs of the four giant planets, orbits began to cross while the Sun was still a red giant. Their conclusion is that the outer solar system's lifetime shrinks from about 10^18 years to around one billion years after the white dwarf forms.

What it means for Earth and Mars

Earth's fate does not change: Mercury, Venus and probably Earth are expected to be swallowed as the Sun expands, Euronews reported, while Mars may sit far enough out to escape. The new study is about what happens next to the giant planets, which were thought to survive in wider orbits almost forever.

How sure is it?

The result depends on how lumpy the Sun's mass loss really is, which no one can watch happen to our own star. The authors chose values they say are consistent with the observed movement of white dwarfs. It is a modelling study, so expect other teams to test it.

For a sense of scale, use our age calculator on your own birthday: even a full human lifetime is less than one ten-millionth of the billion years in question.