The Sun will not explode as a supernova but is destined to become a Red Giant, a transformation that will dramatically alter the Solar System. This stellar transition, occurring over approximately a billion years, will determine the ultimate fate of every orbiting body. A planet’s survival depends entirely on its distance from the Sun when this expansion takes place.
The Sun’s Death: Red Giant, Not Supernova
The Sun’s future begins with a slow, internal fuel crisis. It maintains equilibrium by fusing hydrogen into helium in its core, creating outward pressure that resists gravity. This balance defines its current life stage, the main sequence. When core hydrogen is depleted, fusion slows, and the core contracts, increasing temperature and density. This ignites a shell of fresh hydrogen around the inert helium core, generating intense heat.
The energy from the shell-burning causes the Sun’s outer layers to puff up dramatically, expanding the star hundreds of times its current size. Although the surface will be cooler, its increased luminosity will overwhelm the inner solar system. This expansion defines the Red Giant phase, which ultimately reduces the Sun to a dense stellar remnant.
The Fate of the Inner Planets
The Red Giant expansion means destruction for the four rocky planets. Mercury and Venus will be engulfed and vaporized first. The solar surface is expected to swell out to about 1 Astronomical Unit (AU), the current average distance between Earth and the Sun.
Earth’s fate is complex, depending on the Sun’s expansion and mass loss. The Sun loses mass through stellar winds, weakening its gravitational pull. This causes Earth’s orbit to drift outward, potentially avoiding direct engulfment.
Survival is impossible due to the Red Giant’s extreme heat. Long before maximum size, increasing luminosity will boil away Earth’s oceans and strip its atmosphere. Mars, the outermost rocky planet, will also be rendered uninhabitable by the intense radiation.
Surviving the Expansion: The Outer Solar System
The gas giants and icy bodies beyond Mars are the survivors. Jupiter, Saturn, Uranus, and Neptune are far enough away to avoid engulfment. The Sun’s significant mass loss (about half its total mass) will cause the orbits of these outer planets to expand considerably, shifting them nearly twice as far from the Sun.
Despite the orbital shift, they will experience radical climate change. The Red Giant Sun, thousands of times more luminous, will push the habitable zone far outward (10 to 50 AU). This warmer zone could thaw icy moons like Europa, Enceladus, and Titan, allowing liquid water to exist temporarily.
Kuiper Belt objects, including Pluto, would warm significantly. This warm era will last for hundreds of millions of years until the Red Giant phase ends.
The White Dwarf Era
The Red Giant phase transitions the Sun to its ultimate form. After expanding and contracting, the Sun will shed its outer layers of gas and dust, creating a short-lived planetary nebula. The core will then collapse into a dense, stable remnant called a White Dwarf.
This stellar corpse will be roughly the size of Earth but retain about half of the Sun’s original mass. The surviving outer planets will continue to orbit this tiny, dim object. The White Dwarf will glow faintly from residual heat, cooling slowly over trillions of years, providing long-term stability.