Our Sun is roughly 4.57 billion years old, putting it about halfway through its life. It has enough hydrogen fuel to keep burning steadily for another 5 billion years. After that, it will swell into a red giant, shed its outer layers, and shrink into a dense remnant called a white dwarf. But long before the Sun itself dies, Earth will become uninhabitable.
Earth Gets Too Hot Long Before the Sun Dies
The Sun grows brighter over time, increasing its energy output by about 10% every billion years. Within roughly a billion years from now, that extra heat will be enough to push Earth out of the habitable zone and begin evaporating the oceans. This is the real deadline for life on our planet, not the Sun’s death in 5 billion years.
Scientists debate exactly how fast this plays out. Some models suggest Earth dries out before the billion-year mark, because interactions between a warming climate, rocks, and plate tectonics could accelerate water loss. Others suggest certain life forms could hang on somewhat longer, sustained by periodic chemical cycling from geological processes. Either way, the window for a livable Earth is a fraction of the Sun’s remaining lifespan. By the time the Sun finally exhausts its hydrogen, Mars will sit in the habitable zone while Earth will have been a scorched, waterless world for billions of years.
The Next 5 Billion Years: Steady Burning
Right now, the Sun is in its main sequence phase, fusing hydrogen into helium in its core. This is the long, stable chapter of any star’s life, and for a star the Sun’s size, it lasts about 9 to 10 billion years total. Nothing dramatic happens during this stretch. The Sun gradually brightens and expands slightly, but it remains recognizably the same star. In about 5.4 billion years, the hydrogen fuel in the core runs out, and things change fast.
The Red Giant Phase
Once the core’s hydrogen is spent, the core contracts under its own gravity and heats up while the outer layers of the Sun begin expanding outward. The Sun will balloon into a red giant, swelling to roughly 166 times its current radius. At that size, its surface would extend to about three-quarters of the distance between its current position and Earth’s orbit. Its surface temperature drops to around 3,100 Kelvin (compared to about 5,800 today), giving it a deep red glow, but its total luminosity will be roughly 2,350 times what it is now. A cooler surface spread across that enormous area still radiates a staggering amount of energy.
Inside the core, temperatures climb to extraordinary levels. When the core reaches about 100 million degrees, a new type of fusion ignites: helium atoms begin fusing into carbon in a process called the triple-alpha reaction. Because the core at this point is incredibly dense and compressed, this ignition happens explosively in an event called the helium flash. The flash is entirely internal, so you wouldn’t see a visible explosion, but it fundamentally restructures the star’s core and briefly stabilizes it before the Sun resumes expanding.
Will the Sun Swallow Earth?
This has been debated for decades, but recent modeling published in the journal Astronomy & Astrophysics points to a grim answer: Earth will most likely be engulfed. As the Sun expands, it loses mass, which weakens its gravitational pull and allows planets to drift outward into wider orbits. For a while, researchers hoped this orbital expansion might save Earth. But tidal interactions between the bloated Sun and nearby planets drag them inward, and the math doesn’t work in Earth’s favor. The study found that Earth cannot escape engulfment near the tip of the red giant phase. Interestingly, the researchers also found that engulfment is a somewhat chaotic, stochastic process rather than a perfectly predictable one. A planet starting just a bit farther out (around 1.4 times Earth’s current distance from the Sun) could potentially survive, ending up in a moderately elongated orbit around the remnant star.
Shedding Its Outer Layers
After the red giant phase, the Sun won’t have enough mass to explode as a supernova. Instead, it will pulsate and gradually expel its outer layers into space, creating a glowing shell of gas called a planetary nebula (the name is misleading; it has nothing to do with planets). During this process, the Sun will shed about 40% of its total mass. These expanding clouds of gas enrich the surrounding space with carbon, oxygen, and other elements that eventually get recycled into new stars and planets.
What’s left behind is the exposed core: a small, incredibly dense object called a white dwarf.
The White Dwarf: A Slow Fade
A typical white dwarf is about half the mass of the original star, compressed into an object only slightly larger than Earth. That means a teaspoon of white dwarf material would weigh several tons. The Sun’s white dwarf remnant will initially be extremely hot, glowing white, but it generates no new energy through fusion. It simply radiates away its stored heat into space, growing dimmer and cooler over an immense timescale.
Eventually, after roughly 10 billion more years, the white dwarf will cool to the point where it no longer emits significant light or heat, becoming what’s sometimes called a black dwarf. No black dwarfs exist yet anywhere in the universe because the process takes longer than the current age of the cosmos (about 13.8 billion years). When our Sun finally reaches that stage, it will be a dark, Earth-sized cinder drifting through space, the quiet endpoint of a star that burned for billions of years.
The Full Timeline at a Glance
- Now to ~1 billion years: The Sun brightens enough to evaporate Earth’s oceans and end habitability on our planet.
- ~5.4 billion years: The Sun exhausts its core hydrogen and leaves the main sequence.
- ~5.4 to ~6 billion years: The Sun expands into a red giant, likely engulfing Mercury, Venus, and Earth.
- ~6 to ~7 billion years: The Sun sheds its outer layers, losing about 40% of its mass and forming a planetary nebula.
- ~7 billion years onward: The remaining core persists as a white dwarf, slowly cooling over tens of billions of years into a black dwarf.