A study in Astronomy & Astrophysics has reopened a dramatic question about Earth’s far future. Researchers led by Mats Esseldeurs at KU Leuven used updated stellar and orbital models to show that our planet may survive the Sun’s giant phases, even as Mercury and Venus are swallowed.
The result is a model-based forecast for a world billions of years from now. It offers a more hopeful physical outcome for Earth as a planet, while saying nothing comforting about habitability. Long before the Sun reaches its final stages, rising solar brightness will transform Earth’s surface beyond recognition.
Still, the study matters because Earth is a test case for a wider cosmic problem. Around the galaxy, aging stars shed mass, swell outward and reshape the orbits of their planets. The same physics that decides Earth’s fate also helps astronomers interpret planets found around white dwarfs, the dense remains of stars like the Sun.
A cosmic tug of war
When the Sun exhausts the hydrogen fuel in its core, it will begin a slow transformation into a swollen giant star. Its outer layers will expand far beyond the Sun’s current size. During that stage, nearby planets will feel stronger tidal forces from the bloated star.
Those tides act like a brake on a planet’s orbit. As orbital energy drains away, a planet can spiral inward. For a world too close to the expanding solar surface, that inward drift can end inside the star itself.
At the same time, the future Sun will lose a large amount of material through powerful stellar winds. As the Sun becomes lighter, its gravitational grip weakens. Planets can then move outward into wider orbits. This creates the central contest in the new work, tidal interactions pulling Earth inward against solar mass loss pushing its orbit outward.
“The fate of Earth depends on a delicate balance between these two effects,” Esseldeurs said in a KU Leuven statement. He described the fork in the road clearly: “If tidal interactions dominate, Earth is engulfed. If mass loss dominates, Earth escapes to a wider orbit.”
The new calculations focus on that balance with more detailed treatment of stellar structure and tidal physics. The team modeled the Sun’s life through its giant phases, then followed the changing orbits of the inner planets as the star expanded and shed mass.
What L2 Puppis reveals
A nearby aging star called L2 Puppis gives astronomers a rare glimpse of the kind of stellar future the Sun may face. It sits about 200 light-years away in the constellation Puppis. Astronomers study it because it resembles a more evolved version of a Sun-like star.
L2 Puppis is surrounded by dusty material and appears to be losing mass at a high rate. Previous observations also suggest that a giant planet or companion may orbit within its dusty environment. That makes it a useful comparison point for the late-life behavior of planetary systems.
The KU Leuven-led team used observations of L2 Puppis to constrain how much mass a Sun-like star might lose during the asymptotic giant branch stage. That stage, often shortened to AGB phase, comes after the red giant phase. It is one of the Sun’s last luminous acts before it leaves behind a white dwarf.
This observational anchor matters because mass loss is difficult to predict from theory alone. A small change in the amount of material lost by the Sun can shift Earth’s final orbit enough to change the outcome. In the new models, Earth survives when the Sun loses enough mass during its late giant stages.
L2 Puppis also shows why the problem remains challenging. Dying stars can have dusty winds, uneven outflows and complex interactions with companions. Those details shape the final architecture of planetary systems and astronomers are still building the observational record needed to refine the models.
Mercury and Venus face the fire
The simulations give Mercury and Venus a grim forecast. As the Sun grows into a giant, both inner planets are expected to fall within the expanding stellar envelope. Their orbits place them too close to escape the combined effects of swelling solar layers and tidal drag.
Mercury is the first world in line. It orbits so close to the Sun today that even a moderate solar expansion in the far future would put it in danger. Venus follows because it also sits deep inside the future reach of the aging Sun.
Earth occupies a more precarious boundary. Its current orbit gives it more room than Venus and the Sun’s mass loss may widen that orbit during the giant phases. The models suggest that Earth can shift to a path just outside the Sun’s outer radius, depending on how much mass the star sheds.
That possible survival applies to Earth as a rocky body. By then, the planet’s oceans and atmosphere would have faced catastrophic changes. The study’s question is orbital and planetary survival, centered on whether Earth remains outside the Sun’s extended layers during the final stellar expansion.
Mars fares better in the simulations because it begins farther away. Its orbit also expands as the Sun loses mass. By the time the Sun finishes its giant phases and becomes a white dwarf, the outer solar system would have drifted into a new configuration.
Mass loss may save Earth
The study’s most important uncertainty is now the future Sun’s mass loss. Earlier work differed on tidal assumptions and stellar evolution details. The new modeling narrows part of that uncertainty by treating tides from the internal structure and dynamics of evolved stars.
“The largest uncertainty no longer comes from the tidal calculations, but from how much mass the future sun will lose,” Esseldeurs said. That statement turns attention toward observations of real aging stars, where astronomers can measure winds, dust and mass loss more directly.
In simple terms, the Sun’s gravity depends on its mass. When the Sun ejects its outer layers, all surviving planets feel a weaker central pull. Their orbits expand, much as a ball on a string would move outward if the string’s inward pull gradually relaxed.
Tides complicate that picture because the future Sun will be huge. A planet moving through the gravity field of a swollen star raises tidal bulges in the stellar gas. Those bulges can lag behind the planet’s motion and drain orbital energy. The closer the planet comes to the stellar surface, the stronger the effect becomes.
The team’s updated stellar evolution models and tidal calculations suggest that Earth’s orbit may grow enough to avoid engulfment. The result is cautious, because it depends on assumptions about late-stage winds from Sun-like stars. Still, the direction of the evidence has shifted toward survival under the best current constraints.
PLATO could sharpen the forecast
Better observations could turn this far-future forecast into a sharper prediction. Astronomers need more examples of planets around aging stars, especially systems that resemble the Sun’s future. Those systems show how often planets survive close to expanding giants.
Esseldeurs put the point plainly: “Observations of sun-like giant stars currently point towards Earth’s survival, but we need better observations before we can be certain.” The next generation of planet surveys could supply that missing evidence.
The European Space Agency’s PLATO mission is expected to search for Earth-like planets around Sun-like stars. Its measurements should also help astronomers study planets in more evolved systems. If PLATO finds more worlds near aging stars, researchers can compare those discoveries with models of tidal decay and mass loss.
White dwarf systems offer another clue. Some white dwarfs host surviving planets or planetary debris, showing that planetary systems can endure violent stellar endings in several ways. The new Earth study helps connect those distant systems to the future of our own solar system.
For now, the message is careful and fascinating. Earth’s long-term survival as a planet depends on a race between inward tidal drag and outward orbital expansion. In the new models, mass loss may give Earth just enough distance to outlast the Sun’s final blaze.
