The sun will almost certainly make Earth uninhabitable, though the timeline is measured in hundreds of millions to billions of years. Long before the sun physically swallows our planet, its gradually increasing brightness will boil away the oceans and bake the surface into a lifeless rock. Whether Earth is ultimately consumed during the sun’s final expansion or merely scorched beyond recognition depends on a gravitational tug-of-war that scientists are still working to resolve.
Earth Becomes Uninhabitable First
The sun is getting brighter. Not in any way you’d notice in a human lifetime, but over geological time, the increase is relentless. A rise of just 6 percent in the energy Earth receives from the sun would trigger a runaway greenhouse effect, causing the oceans to begin boiling away into space. Based on that threshold, some models place the end of Earth’s habitability as soon as 650 million years from now.
More recent three-dimensional climate simulations push that deadline further out. These models predict that the tipping point arrives when Earth’s surface temperature reaches roughly 70°C (158°F), which would happen in approximately one billion years. At that point, the oceans start to boil, water vapor traps even more heat, and the greenhouse effect spirals out of control. Other researchers have suggested Earth could remain marginally habitable for up to 1.5 billion years, when the sun will be about 15.5 percent brighter than it is today. Either way, the planet becomes a dry, scorching wasteland long before the sun reaches its most dramatic phase.
The Red Giant Phase
Roughly 6 billion years from now, the sun will exhaust the hydrogen fuel in its core. When that happens, it will begin swelling into a red giant, growing so enormous that its outer edge could extend to about 2 astronomical units from its center. For reference, Earth currently orbits at 1 astronomical unit. Mercury and Venus will be swallowed outright.
Earth’s fate is genuinely uncertain. As the sun balloons outward, it also sheds mass, which weakens its gravitational pull on the planets. That means Earth’s orbit will slowly drift outward, currently expanding at about 2 centimeters per year. By the time the sun reaches its red giant peak, Earth could have migrated far enough to avoid being engulfed.
But there’s a competing force. If the expanding sun gets close enough, tidal drag between the star’s outer envelope and the planet could pull Earth inward. One study modeling this interaction found that once Earth enters the sun’s outer atmosphere, its orbit would decay in roughly 200 years or less, making survival impossible. As astronomer Dimitri Veras at the University of Warwick has put it: “I am confident that the Sun will swallow Mercury and Venus, and not Mars. But the fate of the Earth, which resides in between, is less clear.”
The end of the red giant phase is the most violent period in a star’s life. The dying sun will throw off material in intense bursts, and its diameter could fill the entire sky as seen from any surviving planet nearby. Even if Earth somehow avoids being consumed, it will be a stripped, molten remnant with no atmosphere and no ocean.
What Happens After: The White Dwarf Sun
After shedding its outer layers, the sun will collapse into a white dwarf, a dense, fading ember about the size of Earth but with roughly half its current mass. If our planet survives the red giant phase, its orbit would expand to roughly twice its current distance from the sun, pushed outward by the loss of gravitational pull. But “survival” is generous: Earth would be a burned-out cinder at best.
Observations of other white dwarf systems give us a preview. Up to 50 percent of white dwarfs show signs of rocky material falling onto their surfaces, with compositions strikingly similar to objects in our own solar system. Asteroids and planetary remnants get pulled apart by the dead star’s intense gravity, forming discs of debris that slowly spiral inward. At one white dwarf system, astronomers watched an infrared outburst brighten the star by a dramatic amount within just six months, likely caused by collisions among orbiting planetary fragments. This kind of activity appears to be common, not rare.
We Have Other Stars to Watch
Nearly every known planetary system orbits a star that will eventually become a white dwarf, or already has. Giant branch evolution and stellar mass loss dramatically reshape the architecture of these systems, scattering planets and pulverizing asteroids. But planetary material persists. The rocky building blocks don’t vanish; they just get rearranged, sometimes violently. What astronomers see at white dwarfs across the galaxy is likely a preview of our own solar system’s distant future: fragments of once-intact worlds slowly being consumed by a stellar corpse.
Nearer-Term Solar Risks
The sun won’t physically threaten Earth for hundreds of millions of years, but it can still cause serious problems on much shorter timescales. Powerful solar storms, similar to the 1859 Carrington Event, can knock out power grids, disable satellites, and disrupt communications. Estimates for the probability of a Carrington-level storm during any given solar cycle vary wildly, from about 1 percent to as high as 25 percent. A storm like that wouldn’t damage the planet itself, but it could cause widespread infrastructure failures lasting weeks or months.
These events are a fundamentally different category of threat from the sun’s long-term evolution. Solar storms are manageable with better forecasting and hardened infrastructure. The gradual brightening of the sun and its eventual expansion into a red giant are not problems with engineering solutions on Earth. They represent a hard expiration date for our planet’s ability to support life, one that arrives long before the sun ever physically reaches us.