Yes, the Sun will almost certainly engulf the Earth. In roughly 6 billion years, the Sun will exhaust the hydrogen fuel in its core and swell into a red giant star, expanding so dramatically that it will consume Mercury, Venus, and Earth. While there’s a competing effect that pushes Earth’s orbit outward as the Sun loses mass, detailed calculations show it won’t be enough to save our planet.
Why the Sun Will Expand
The Sun is currently about 4.5 billion years old, roughly halfway through its life as a stable, hydrogen-burning star. Stars like the Sun burn for about 9 to 10 billion years total. When the hydrogen in the core finally runs out, the core will contract under gravity, heating up enough to start fusing helium into carbon. Meanwhile, the outer layers of the Sun will balloon outward.
During this red giant phase, the Sun’s radius is expected to grow from its current size to somewhere around 1 to 2 astronomical units (AU). One AU is the current distance between Earth and the Sun, about 93 million miles. At its maximum expansion, the Sun could swell to roughly twice that distance, making Earth’s current orbit fall well within the bloated star’s outer atmosphere.
The Tug of War: Mass Loss vs. Tidal Drag
This isn’t quite as straightforward as a balloon inflating around a stationary marble. Two competing forces shape Earth’s fate, and for a long time, astronomers debated which one would win.
As the Sun expands, it also sheds mass. A lighter Sun exerts less gravitational pull, which means Earth’s orbit naturally drifts outward. Even now, the Sun’s gradual mass loss causes Earth to recede by about 2 centimeters per year. Over billions of years, that adds up. Some researchers initially hoped this orbital expansion would let Earth stay just ahead of the Sun’s growing edge.
But working against that escape is tidal interaction. As the Sun’s outer layers creep closer to Earth, gravitational tides between the two bodies transfer energy from Earth’s orbit into the Sun’s envelope. This acts like a drag force, pulling Earth inward. There’s also physical drag from the thin but real gas in the Sun’s lower atmosphere, which Earth would begin plowing through as the two get close.
A detailed study published in the Monthly Notices of the Royal Astronomical Society modeled both effects step by step through the Sun’s evolution. The conclusion: Earth will not escape engulfment. The orbital expansion from mass loss helps, but it’s not enough to overcome the inward pull of tidal and atmospheric drag. The study found that a planet would need to orbit at least 1.15 AU from the Sun today to survive the red giant phase. Earth sits at 1.0 AU.
Mercury and Venus Go First
Earth won’t be alone. Mercury and Venus, orbiting much closer to the Sun, will be swallowed earlier and with far less uncertainty. Mercury orbits at just 0.39 AU and Venus at 0.72 AU, both deep inside the danger zone. By the time the expanding Sun reaches Earth, those two planets will have been consumed long before. In 2023, Caltech researchers reported the discovery of a planet that had survived engulfment by its own star, confirming that this process really does happen, but also showing it takes extraordinary circumstances for a planet to come out the other side.
Earth Becomes Uninhabitable Long Before
The engulfment itself is billions of years away, but Earth’s expiration date as a livable world comes much sooner. The Sun grows about 10% brighter every billion years. That sounds modest, but it’s enough to push Earth out of the habitable zone, the range of distances where liquid water can exist on a planet’s surface.
Within roughly one billion years, the Sun will be bright enough to begin evaporating Earth’s oceans. Once that process starts, the water vapor in the atmosphere will trap even more heat, accelerating the warming in a runaway feedback loop. Some estimates suggest certain hardy life forms could persist a bit longer thanks to differences in biological needs and ongoing geological processes like plate tectonics releasing essential chemicals. But the broad scientific expectation is that complex life on Earth has no more than about a billion years left, not six.
So while the dramatic image of Earth being swallowed by a giant red Sun is real, it’s the slow brightening over the next billion years that represents the more meaningful deadline for life on this planet.
What Happens After Engulfment
The Sun’s red giant phase isn’t the final chapter. After burning through its helium fuel, the Sun won’t be hot enough to fuse the carbon that has built up in its core. Without a new energy source, the core contracts again, releasing energy that puffs the outer layers out even further. The Sun becomes unstable, pulsating and shedding mass in waves.
Eventually, the Sun blows off its entire outer envelope, leaving behind a dense, Earth-sized core called a white dwarf. The ejected gas forms a glowing shell known as a planetary nebula, a brief and beautiful phase that lasts tens of thousands of years. The transition from red giant to white dwarf takes roughly 75,000 years for a star of the Sun’s mass.
The white dwarf that remains will be incredibly dense and initially very hot, but with no fuel left to burn, it will slowly cool over billions of years. After perhaps 10 billion more years, it will fade into a cold, dark object sometimes called a black dwarf, a stellar ember radiating almost nothing into space. Whatever remains of the inner solar system at that point will orbit a faint, cooling cinder in near-total darkness.