The Sun, which sustains life on Earth, is currently in a stable phase. Like all stars, it has a finite lifespan, undergoing predictable transformations. These changes will ultimately reshape our solar system, dramatically altering the environments of all planets.
The Sun’s Final Stages
The Sun is currently in its main sequence phase, fusing hydrogen into helium in its core. Approximately 5 billion years from now, it will exhaust this fuel, beginning a dramatic transformation. The core will then contract and heat up, igniting a shell of hydrogen fusion around the core. This process will cause the Sun’s outer layers to expand significantly, turning it into a red giant.
During its red giant phase, the Sun will swell to over 200 times its current radius, potentially reaching Earth’s orbit. Its surface temperature will decrease, giving it a reddish-orange hue, while its luminosity will increase dramatically. After about a billion years, the Sun will become unstable and shed its outer layers, forming a planetary nebula. This expulsion will leave behind the Sun’s dense, hot core, which will evolve into a white dwarf star.
The Inner Planets’ Demise
As the Sun expands into a red giant, the inner planets face a destructive future. Mercury and Venus, closest to the Sun, will be engulfed and vaporized by its expanding outer layers.
Earth’s fate is less certain but dire. The Sun’s expansion will cause intense heating, boiling away its oceans and stripping its atmosphere long before direct engulfment. While some models suggest Earth might escape direct engulfment if its orbit expands due to the Sun’s mass loss, it would still become an uninhabitable, scorched cinder. Tidal forces and atmospheric drag from the Sun’s extended envelope could also pull Earth inward, leading to its eventual consumption.
Mars, located further out, will likely avoid direct engulfment. However, it will experience a significant temperature increase, melting any remaining surface ice. Despite surviving engulfment, Mars’ surface would become inhospitable due to the intense heat and radiation from the Sun.
The Outer Planets’ Transformation
The outer gas giants—Jupiter, Saturn, Uranus, and Neptune—are far enough from the Sun to avoid engulfment. However, they will still undergo substantial transformations due to the Sun’s increased luminosity and heat. This warming could cause their atmospheres to expand.
The icy moons orbiting these planets, such as Europa and Enceladus, might experience significant ice melting, potentially forming temporary liquid oceans. As the Sun loses mass during the red giant phase, its gravitational pull on the planets will weaken. This mass loss will cause the outer planets’ orbits to expand, moving them further from the dying star. Objects in the distant Kuiper Belt and Oort Cloud will also warm, but are expected to remain gravitationally bound to the solar system.
The Solar System’s Distant Future
After the red giant phase, the Sun will settle into its final stellar remnant form: a white dwarf. This compact object will be roughly the size of Earth but will contain about half of the Sun’s original mass, making it incredibly dense. A white dwarf generates no new heat through fusion but radiates away its residual thermal energy, slowly cooling over billions of years. It will be composed primarily of carbon and oxygen.
The outer planets, and any inner planets that may have survived the red giant phase in a highly altered state, will continue to orbit this white dwarf. Observations of other star systems have revealed exoplanets, including gas giants and even rocky planets, orbiting white dwarf remnants, suggesting that our outer planets could persist. Over extremely long timescales, possibly trillions of years, the white dwarf will theoretically cool down to a “black dwarf,” a cold, dark, and theoretical stellar corpse that emits no light or heat. The universe is not yet old enough for any black dwarfs to have formed. In this incredibly distant future, the solar system will be a place of extreme cold and darkness, with the remaining planets becoming frozen, dark worlds, potentially subject to gravitational interactions that could eventually eject them into interstellar space.