The Sun will not end its existence in a spectacular supernova explosion, a fate reserved for much more massive stars. Instead, in approximately five billion years, our Sun will undergo a profound transformation, evolving through stages that will dramatically alter its appearance and impact the solar system. This stellar metamorphosis will result in a visual spectacle: first an expanding giant, then a faint remnant. This process reveals the Sun’s true, less explosive, end.
The Sun’s True Fate
The Sun, currently a main-sequence star, generates energy by fusing hydrogen into helium in its core. As the hydrogen fuel in its core depletes, the fusion process will cease, causing the core to begin collapsing under its own gravity. This collapse will increase the core’s temperature and pressure, igniting a shell of hydrogen fusion around the inert helium core. This renewed fusion will cause the Sun’s outer layers to expand significantly, transforming it into a red giant.
During this red giant phase, the Sun’s core will continue to contract and heat up until it becomes hot enough to fuse helium into carbon and oxygen. After exhausting its helium fuel, the Sun will shed its outer layers into space, forming a transient planetary nebula. What remains will be the Sun’s dense, hot core, known as a white dwarf. This white dwarf will be roughly the size of Earth but will contain about half of the Sun’s original mass.
The Initial Visual Transformation
As the Sun transitions into a red giant, its visual appearance from Earth will change profoundly over approximately one billion years. The Sun will expand dramatically, growing to between 100 and 250 times its current diameter. This immense expansion will cause its color to shift from its current yellow-white to a more orange-red hue. Despite its cooler surface temperature, the Sun’s sheer size will make it significantly more luminous.
From Earth’s perspective, the expanding Sun will appear to grow larger and larger in the sky, eventually dominating the entire horizon. Mercury and Venus will be engulfed by the Sun’s expanding outer layers, disappearing from view as the Sun swells. The sky would likely darken significantly, though not to black, as the immense, glowing red orb fills the view.
Immediate Earthly Consequences
Long before Earth is potentially engulfed, its conditions will become uninhabitable as the Sun expands. The increasing heat and radiation from the growing red giant Sun will trigger a runaway greenhouse effect. Earth’s oceans will boil away, and its atmosphere will eventually be stripped into space.
Earth’s ultimate fate remains a subject of scientific modeling, with some scenarios suggesting it will be completely engulfed by the Sun. If engulfed, Earth would either vaporize entirely or spiral inwards due to frictional drag within the Sun’s tenuous outer atmosphere. However, some models propose that Earth might migrate outward as the Sun loses mass, potentially escaping direct engulfment. Even if Earth avoids being consumed, it would be a barren, scorched planet devoid of any life.
The Final Stage from Afar
After the red giant phase, the Sun will become a white dwarf, a remarkably compact and dense stellar remnant. It will no longer generate energy through fusion, instead glowing faintly from residual heat, gradually cooling over billions of years.
The planetary nebula, formed from the Sun’s expelled outer layers, will slowly dissipate into interstellar space. The inner planets, Mercury, Venus, and likely Earth, will no longer exist, having been destroyed during the red giant phase. The outer planets are expected to survive, orbiting the dim white dwarf in significantly wider paths due to the Sun’s mass loss. The solar system will become a desolate place, with a silent, cooling stellar corpse at its center and distant, cold planetary remnants.