The Solar System
4.6 billion years ago, a giant molecular cloud collapsed under gravity, forming the Sun and everything orbiting it — from rocky inner planets to icy outer worlds, asteroid belts and comets.
The Nebular Hypothesis
A giant cloud of gas and dust — enriched by generations of supernovae — began to collapse around 4.6 billion years ago. As it collapsed, it spun faster (conservation of angular momentum) and flattened into a protoplanetary disk. The center grew hot enough for hydrogen fusion to ignite: our Sun was born.
Within the disk, dust grains collided and stuck together, forming pebbles, then boulders, then planetesimals — the building blocks of planets. Over millions of years, these collided and merged, creating the four rocky inner planets and the cores of the outer gas giants.
Earth's Violent Birth
The young Earth was a hellish world — repeatedly bombarded by asteroids and comets, its surface a global ocean of magma. Around 4.5 billion years ago, a Mars-sized body called Theia collided with Earth in one of the most cataclysmic events in our solar system's history.
The debris from this Giant Impact coalesced in orbit to form the Moon. This event also tilted Earth's axis to 23.5°, giving us our seasons, and slowed Earth's rotation. Without this impact, Earth might be a very different — and perhaps lifeless — world.
The Eight Planets
Smallest planet, no atmosphere, extreme temperature swings.
Hottest planet (465°C) due to a runaway greenhouse effect.
The only known planet with liquid water oceans and life.
Home to Olympus Mons — the largest volcano in the solar system.
Largest planet; its Great Red Spot is a storm 350+ years old.
Its iconic rings are made of ice and rock, up to 30 meters thick.
Rotates on its side at 98° axial tilt.
Winds exceed 2,000 km/h — the fastest in the solar system.
The Sun — Our Star
The Sun contains 99.86% of all mass in the solar system. Its core temperature reaches 15 million K, fusing 600 million tonnes of hydrogen into helium every second. It is a middle-aged G-type main-sequence star, halfway through its ~10 billion year lifespan. In 5 billion years, it will expand into a red giant, engulfing Mercury, Venus, and possibly Earth — before collapsing into a white dwarf.