Scientists have long predicted that when the Sun runs out of fuel in roughly five billion years, Earth will burn.
The picture was fairly settled: the Sun expands, tidal forces drag the planet inward, and engulfment follows.
That conclusion rested on one specific assumption about how energy bleeds away inside a bloated, aging star.
A new study went back and rebuilt that part of the physics.
Different numbers produce a different ending – and by the updated reckoning, Earth slips out rather than falls in.
The stronger of two opposing forces
Two competing effects decide Earth’s fate. As the aging Sun sheds material into space, its hold on the planets loosens and their orbits widen.
Tidal forces push the opposite way, tugging a planet back toward the star.
The research team was led by Mats Esseldeurs, an astrophysicist at the Institute of Astronomy at the Catholic University of Leuven (KU Leuven) in Belgium.
The researchers modeled how Earth’s orbit changes as the Sun ages. Whichever effect wins settles whether the planet escapes or falls in.
If tidal dragging dominates, Earth spirals inward and the Sun consumes it. Should the mass loss win out, the planet moves outward fast enough to keep its distance.
The whole question comes down to which force the models say is stronger.
Worlds that vanish
Stars really do devour their planets. In 2023, astronomers caught the act in real time, watching a distant Sun-like star flare as it swallowed a world that had wandered too close.
It was the first direct case of its kind. Our own Solar System will lose worlds the same way.
As the Sun becomes a red giant, the model shows it overtaking Mercury and Venus during its first growth spurt, while Earth and Mars retreat fast enough to survive that round.
The Sun’s expansion is not one smooth event. After the first bout of swelling, the star shrinks back, then balloons again in an even larger surge later on.
Earth’s survival hangs on that second, fiercer phase.
Rethinking the tides
The new work breaks from the past on one specific point.
Earlier studies used simplified descriptions of how tides bleed energy inside a bloated star, and those predicted a strong inward pull.
That pull was strong enough, in most versions, to doom Earth.
Esseldeurs and his colleagues rebuilt that piece of the physics from the ground up, drawing on the latest understanding of how material churns inside an old star.
Their models suggest the energy drains away more gently than older formulas assumed, leaving a weaker tug on any orbiting planet.
Surviving the second expansion
The gap between the old and new models is widest right at Earth’s distance, which makes the choice of approach decisive for our planet.
Run the updated physics, and Earth pulls through both of the Sun’s growth spurts instead of spiraling in.
Until this analysis, the leading models had Earth burning up during that second expansion.
Flipping that verdict is the central result – and it rests entirely on treating the tides with more care than earlier work could manage.
The Sun’s fading mass
Tides are only half the story. How much weight the Sun sheds as it dies counts just as much, and proves far harder to pin down. Estimates from different methods disagree by more than a factor of ten.
Faster weight loss loosens the Sun’s grip sooner, flinging the planets outward and helping Earth escape.
If the loss is too slow, though, the star stays massive with a longer reach, favoring engulfment. Earth’s fate flips with whichever rate is truer.
Late in its life the Sun also goes through brief pulses, each only a few hundred years long, when it puffs up sharply.
Should its weight loss run low, one of these surges could briefly reach toward Earth. Whether the planet would actually be lost during such a short window remains unclear.
A preview next door
To anchor the Sun’s future weight loss, the team turned to an aging star named L2 Puppis, born at almost exactly the Sun’s mass.
Well into its own decline, it serves as a preview of the Sun billions of years from now.
L2 Puppis wears a disk of dust and may even host a planet of its own. Measurements of how fast it sheds mass disagree widely, so it carries its own doubts – yet it beats relying on theory alone.
Feed its observed behavior into the model, and Earth comes out a survivor.
Real worlds back the idea too. Astronomers have found a rocky planet circling a burned-out star, a white dwarf, that appears to have outlived its sun’s giant years.
What comes next
The takeaway is not that Earth is safe for certain. It’s that the most current physics tips the odds toward survival rather than destruction, undoing a conclusion the field had mostly settled on.
A nearby aging star, observed directly, leans the same way.
For astronomers, the payoff reaches past our own Sun. The same models decide which planets elsewhere can outlast their stars, sharpening the hunt for worlds that endure into old age.
More help is on the way. A space telescope launching soon, built to hunt planets around distant stars, should turn up many circling old, swollen suns.
That mission lets astronomers study such endings in bulk, and could finally tell us how common it is for Earth-sized worlds to drift free rather than disappear.
The study is published in the journal Astronomy & Astrophysics.
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