For as long as astronomers have understood how stars like ours die, the ending written for Earth has been a fiery one: the aging Sun swells into a red giant and swallows the planet whole. A study published Friday in the journal Astronomy & Astrophysics complicates that obituary. Its authors calculate that Earth may instead drift outward and slip the Sun’s grasp, surviving our star’s violent old age rather than being consumed by it.
The reprieve, if it can be called that, lies roughly five billion years in the future — and the researchers are blunt that it would arrive long after all life on Earth has been wiped out. What makes the finding notable is not comfort but reversal: it unsettles an assumption that has sat in textbooks since scientists first traced the death of Sun-like stars.
The drama turns on a tug-of-war. When the Sun burns through the hydrogen in its core, it will go through two enormous expansion phases — first becoming a red giant, then, once its helium is exhausted, an “AGB” star, short for asymptotic giant branch. As it balloons outward, two opposing forces decide Earth’s fate. Swelling gravity drags the planet inward toward the fire. At the same time, the dying star bleeds away vast amounts of its own mass on a powerful stellar wind, loosening its hold and letting orbiting planets drift farther out.
The deciding factor is tides — the same physics that raises the oceans and, over eons, nudges the Moon away from us. As the Sun’s bloated surface creeps toward Earth, tidal waves churn inside the star itself; when that energy dissipates, it hauls a planet inward to destruction. Whether Earth lives or dies comes down to which effect wins.
“Earth’s fate depends on a delicate balance between these two effects. If tidal interactions predominate, Earth is engulfed by the Sun. If the Sun’s mass loss predominates, Earth escapes into an orbit larger than the radius of its star.”
Mats Esseldeurs, lead author, astrophysicist at Belgium’s University of Leuven
Earlier work leaned toward engulfment, but it rested on relatively crude descriptions of how tides dissipate inside a swollen star. That is where the new paper stakes its claim. Modelling of stellar tides has sharpened considerably over the past 15 years, and the team used those improved tools to argue that the energy bleeds off more gently than once thought. “The dissipation is lower than previously expected,” co-author Stephane Mathis, an astrophysicist at France’s CEA Paris-Saclay centre, told AFP. A weaker inward tug tilts the balance toward escape.
To estimate how much mass the Sun could shed in its death throes, the researchers did not rely on theory alone. They anchored their numbers to a real object — a nearby star called L2 Puppis, which Mathis described as the Sun’s “old cousin.” It is an AGB star far enough along its own decline to serve as a working preview of the Sun’s future, and its observed mass-loss rate fed directly into the model.
- The Sun’s red giant and AGB phases are still about 5 billion years away.
- Earth’s survival hinges on two competing forces: tidal capture versus mass loss from the dying Sun.
- Improved tidal modelling over 15 years shifted the verdict from engulfment toward escape.
- The nearby AGB star L2 Puppis served as the real-world proxy for the Sun’s future mass loss.
The conclusion comes wrapped in caution, and deliberately so. This is a model, not an observation; the language throughout is conditional.
“A better understanding of tidal physics and the most advanced constraints we have on mass loss allow us to say that — in the current state of knowledge — Earth could move away from the Sun, contrary to what was predicted before.”
Stephane Mathis, co-author, CEA Paris-Saclay
Earth would not be alone in dodging the fire. By the same modelling, Mars also escapes a death spiral. The two planets nearest the Sun are far less fortunate: Mercury and Venus, the study finds, will be inexorably swallowed by the expanding fireball — a fate that lends a grim edge to recent speculation about whether anything could ever survive in Venus’s clouds. The reordering of the inner solar system would be total.
It is worth keeping the reprieve in proportion. A surviving orbit is not a surviving world. Long before the Sun reaches red giant size, its steady brightening will have boiled away Earth’s oceans and sterilised the surface, a slow catastrophe that astronomers reckon plays out hundreds of millions of years from now — a reminder that the Sun does not need to touch Earth to reshape life on it. What the new work changes is the manner of the planet’s end, not whether it ends. After its giant phases, the Sun will shrink into a white dwarf, an Earth-sized ember no longer capable of fusion, cooling and dimming across the deep future. Whether a charred, airless Earth is still circling it then is the question this study reopens — and, for once, the answer it offers is escape rather than incineration. For sky-watchers more interested in the present, the same patch of cosmos keeps offering closer spectacles, from colliding galaxy clusters to planetary conjunctions, no five-billion-year wait required.
