In a few billion years, our Sun will become so violently hot that it could wipe out all life in the Milky Way. Yet, paradoxically, the same star that could destroy life may also help make distant worlds like Pluto and Saturn’s moons habitable. How can the center of our Solar System be so both giving and destructive? Here’s a detailed journey through the life of our Sun, from its birth to its eventual death.
1 Day Old: The Birth of the Solar System
Around 4.6 billion years ago, the first outlines of our Solar System began to emerge. The remnants of older stars, scattered across space after supernovae, created vast clouds of gas, dust, and vapor. Under gravity’s influence, this gaseous cloud began collapsing and spinning, forming a dense central core.
Around this core, the remaining material flattened into a rotating disc. Small clumps of dust and gas gradually collided and stuck together, forming the early building blocks of planets. Meanwhile, the central core grew hotter and denser, becoming a protostar, a baby Sun made mostly of hydrogen and helium.
Within just 10 million years, the gas giants Jupiter, Saturn, Uranus, and Neptune had begun forming. By 50 million years, the protostar reached a critical milestone: nuclear fusion. Hydrogen atoms fused into helium, releasing enormous energy, marking the true birth of our Sun. The inner rocky planets, Mercury, Venus, Earth, and Mars, formed shortly thereafter.
50 Million Years Old: The Sun’s Childhood
Now powered by nuclear fusion, the Sun entered its early life. It burned approximately 603 billion kilograms of hydrogen every second, releasing enough energy in a single moment to power every home on Earth for 800,000 years. The surface temperature reached 5,500 degrees Celsius, with a core of 15 million degrees Celsius.
The Sun was perfectly sized. Smaller, and it might have become a dim brown dwarf incapable of sustaining life on Earth. Larger, and it would have burned out far too quickly. Inside, a delicate balance called hydrostatic equilibrium kept the star stable, with gravity pulling inward and fusion energy pushing outward. This balancing act would continue for billions of years.
230 Million Years Old: The First Galactic Orbit
By this age, our Solar System had completed its first orbit around the Milky Way, 230 million Earth years. The young Sun was only 70% as bright as it is today, slowly maturing.
During this period, a gradual but crucial change began: the Sun’s brightness started increasing. As helium built up in the core, pressure rose, temperatures climbed, and luminosity slowly intensified. Though incremental at first, these changes would eventually have dramatic effects on life on Earth.
4.6 Billion Years Old: The Modern Sun
Today, the Sun is middle aged, rotating once every 27 days. It is about 30% brighter than its adolescent self, with nuclear fusion reactions still roaring in its core. The Sun has roughly 5 billion years left before its hydrogen fuel begins to run out.
If the Sun were significantly larger or smaller, Earth might never have developed life. Fortunately, its size and energy output have allowed life to flourish. But its slow evolution also signals a warning: eventually, the Sun will change in ways that could make Earth uninhabitable.
5.2 Billion Years Old: Rising Temperatures
In just 600 million years, the Sun’s luminosity will rise by 6%, increasing the solar radiation reaching Earth. This added heat will cause carbon dioxide to leave the atmosphere, halting photosynthesis. Plants will die, followed by animals. Only the oceans may sustain some life.
5.6 Billion Years Old: Earth Becomes a Greenhouse
Another 400 million years on, the Sun will be 10% brighter than today. Helium accumulation will increase the Sun’s core temperature, creating a runaway greenhouse effect on Earth. Oceans will evaporate, the atmosphere will saturate with water that breaks down into hydrogen and oxygen, and the planet will become a lifeless rock. Humanity will need to migrate elsewhere, perhaps to other planets or even galaxies.
9 Billion Years Old: The Sun’s Red Phase
Nearly 4.8 billion years in the future, the Sun will enter its “angry old man” stage, becoming 67% brighter. Hydrogen in the core will deplete, outer layers will expand, and the Sun will appear as a bright red sphere in the sky, one and a half times the size of the Moon. Earth, scorched to 300 degrees Celsius, will be uninhabitable.
11 Billion Years Old: Red Giant Transformation
As the Sun exhausts its core hydrogen, helium piles up. Core pressures and temperatures rise, igniting the shell around the core. Within 500 million years, the Sun’s luminosity will be 34 times greater than today. Earth will melt into a sea of molten metals.
Despite this catastrophic energy release, some distant moons may become habitable. Saturn’s moon Titan, with melted ice forming liquid oceans, and even Pluto, could briefly resemble tropical paradises.
12 Billion Years Old: Helium Flash and Subgiant Phase
By this stage, the Sun is burning fuel at an unsustainable rate. Its core temperature reaches 100 million Kelvin, triggering a helium flash. In minutes, 6% of the helium core burns explosively. The Sun briefly outshines every star in the Milky Way, then cools and shrinks into an orangish yellow subgiant. Over 100 million years, it burns helium at 100 times the previous rate, forming a carbon oxygen core.
12.1 Billion Years Old: The Final Red Giant
After exhausting its helium, the Sun expands into a Red Giant with a carbon core. The outer layers are violently ejected into space, with half dispersing into the interstellar medium and half falling into the dense white dwarf core. Planetary orbits weaken, but some objects, including Jupiter and bodies in the Kuiper Belt, remain gravitationally bound. The Solar System as we know it will survive, but its planets will be unrecognizable.
