The Sun has a predictable life cycle that will ultimately determine the fate of our planet. In approximately five billion years, the Sun will run out of the primary fuel source that powers its current stable phase. This exhaustion of hydrogen fuel will trigger a series of dramatic transformations, causing the star to swell into a Red Giant before finally collapsing into a White Dwarf. Understanding this stellar evolution allows scientists to forecast, with a high degree of certainty, the eventual destruction of Earth.
The Sun’s Slow Transformation (Increased Heat and Luminosity)
Earth will become uninhabitable long before the Sun leaves its stable, main-sequence phase. As hydrogen fuel converts into helium, the inert helium ash accumulates, causing the core to contract. This contraction increases the pressure and temperature in the remaining shell of hydrogen surrounding the core, leading to an accelerated rate of fusion.
This increased fusion means the Sun’s overall luminosity steadily rises, becoming about 10% brighter every 1.1 billion years. In roughly one billion years from now, this gradual increase in heat will be sufficient to push Earth out of the Sun’s habitable zone. The average global temperature will climb high enough to trigger a runaway greenhouse effect.
The rising heat will cause the oceans to evaporate, turning Earth into a scorching, waterless world similar to Venus. With the oceans gone, the planet’s natural carbon cycle will cease, and all surface life will become extinct. By the time the Sun is 4.8 billion years older, its luminosity will be 67% higher, transforming the planet into roasted, bare rock.
Earth’s Fate During the Red Giant Expansion
The most dramatic phase of the Sun’s death begins when it exhausts the hydrogen fuel in its core, triggering the Red Giant phase. The core, now mostly helium, contracts further, and the outer layers expand due to intense energy output from the hydrogen-fusing shell surrounding the core. The Sun’s radius will inflate to more than 100 times its current size.
This expansion will engulf the orbits of the innermost planets, Mercury and Venus, which will be vaporized within the star’s hot, tenuous atmosphere. The Sun’s enormous size will push its atmosphere out to about one Astronomical Unit (AU), the current distance between the Sun and Earth. During this phase, which will last for about a billion years, the surface temperature on Earth will reach hundreds of degrees Celsius.
Even if Earth is not immediately swallowed, it will be subjected to catastrophic levels of heat flux. This extreme energy will melt the planet’s surface, turning it into a molten cinder, and completely strip away any remaining atmosphere. The intense radiation will leave the planet sterilized and structurally compromised, orbiting deep within the fiery atmospheric layers of the Red Giant. The expansion is expected to reach 1.2 AU, placing Earth squarely within the star’s atmosphere for a prolonged period.
The White Dwarf Remnant and a Frozen Earth
After the Red Giant phase, the Sun will undergo a final, rapid transformation. The star will shed its vast outer layers into space, forming a glowing shell of gas known as a planetary nebula. This mass-loss event will be brief but significant, reducing the Sun’s mass by up to 50%.
What remains is the Sun’s core, collapsing into a White Dwarf. This remnant is dense, packing about half of the Sun’s original mass into a sphere roughly the size of Earth. It no longer generates energy through fusion but shines dimly from residual thermal energy, cooling down extremely slowly over trillions of years.
If Earth were to survive the prior Red Giant expansion, it would orbit this tiny, dense stellar remnant. The environment would be dark and cold, with the White Dwarf providing minimal heat and light. The planet, already stripped of its atmosphere and oceans, would become a frozen, lifeless world of rock and metal.
The White Dwarf’s habitable zone, where a planet could potentially maintain liquid water, would be extremely close to the star due to its low luminosity. However, any planet in this close-in zone would likely have been destroyed during the Red Giant phase. The long-term fate of a surviving Earth is one of deep cold and perpetual twilight.
Will Earth Be Physically Swallowed?
Whether Earth will be physically engulfed by the Red Giant is a complex matter of celestial mechanics, dependent on two opposing forces. The first factor is the Sun’s mass loss during the Red Giant phase, which weakens its gravitational pull. This weakening would cause Earth’s orbit to expand outward, potentially pushing it far enough away to avoid the swelling stellar surface.
The second factor is tidal drag created by the Red Giant’s expanded atmosphere. As the Sun swells, its outer layers will become so large that they begin to interact gravitationally and frictionally with Earth. This drag would cause the planet’s orbit to decay, pulling it inward toward the star’s core.
Scientific models suggest that tidal drag is likely to dominate orbital mechanics, or at least counteract the mass-loss effect enough to doom the planet. While Mercury and Venus are certain to be consumed, the fate of Earth is a very close call. Some models predict Earth will survive, while others indicate the planet will spiral into the Sun just before the star reaches its maximum size.
Even in the most optimistic scenario, where Earth’s orbit expands and the planet avoids physical engulfment, it will be left as a scorched, tidally-locked remnant. The extreme heat and radiation from the Red Giant will have long since destroyed the surface and atmosphere, guaranteeing the end of the Earth as a recognizable world.