Sun's death throes may eject planets 100 times sooner than previously thought, scientists warn

Scientists have revised previous predictions about the end of our solar system, warning that the planets could fall into chaos and some may be ejected much sooner than anticipated. New calculations suggest this chaotic phase could begin as little as one billion years after the sun transforms into a white dwarf, approximately 10 billion years from now.

This revised timeline stems from the understanding that the sun's death will not be a smooth process. Instead, it will involve a series of violent 'kicks' as the star sheds its outer layers. These ejections, driven by the sun's mass loss, are expected to destabilize the orbits of the outer planets.

The Sun's Final Stages

All stars, including our sun, exist in a delicate balance between gravity and the outward pressure from nuclear fusion in their core. In about four to five billion years, the sun will exhaust its hydrogen fuel. It will then begin fusing helium, causing its outer layers to expand dramatically, turning it into a red giant. Eventually, the star will shed these outer layers, leaving behind a dense stellar core known as a white dwarf.

Previous models assumed this mass loss would occur gradually and evenly, with the sun shedding about 46% of its mass in a steady stream. This slow dissipation was thought to be insufficient to significantly alter the gravitational center of the solar system, leaving the outer planets' orbits stable for at least 100 billion years, with Uranus's orbit stable for a quintillion years.

However, data from the European Space Agency's Gaia orbital observatory indicates a more turbulent transition. Researchers now believe the sun's mass loss will happen in discrete, powerful ejection events, akin to large coronal mass ejections. An estimated 4,600 such events could occur, each releasing a small fraction of the sun's mass, equivalent to about 33 Earths. While each individual ejection might impart only a minor push to the sun, the random distribution of these 'kicks' can cumulatively destabilize the solar system.

Simulations of Solar System Chaos

Professor Jim Fuller, a theoretical physicist at Caltech and co-author of the study published in The Astrophysical Journal Letters, explained that these kicks can slightly alter the sun's speed. "Each one of these gives a small 'kick' to the Sun, which causes the planetary orbits to become slightly eccentric," Fuller stated. "A series of these kicks builds up the eccentricity, which causes the planets to gravitationally interact with each other, eventually destabilizing their orbits so that they crash into each other, or eject one another from the solar system."

To explore these possibilities, researchers ran 700 simulations. These models indicated that planetary orbits could become chaotic much sooner than previously believed. In nearly 80% of the most likely scenarios, the outer planets began crossing paths before the sun finished shedding its outer layers. In some extreme cases, the outer planets were found to be wandering through each other's orbits when the sun had lost only 10% of its mass.

More alarmingly, the simulations suggest that at least one of the gas giants, Jupiter or Saturn, is likely to be ejected from the solar system altogether in about nine out of ten simulations. In a few instances, Saturn was ejected within millions of years after the sun began its mass-loss phase.

Implications for Earth and Beyond

Despite the dramatic potential end for the outer solar system, the fate of the inner planets, including Earth, remains unchanged. Professor Fuller noted, "The fate of the inner planets – Mercury, Venus, Earth – doesn't really change. They will be swallowed by the Sun when it evolves into a red giant in about five to six billion years."

While these events are far in the future and will occur long after Earth is likely uninhabitable, the findings have implications for understanding the broader galaxy. Scientists are increasingly discovering 'rogue planets'—planets drifting freely in interstellar space without a star. The chaotic end of solar systems, as depicted in these simulations, could account for a significant number of these free-floating celestial bodies. Researchers estimate that rogue planets may outnumber star-bound planets in our galaxy by as much as six to one.