Build a Planet
Seven steps that take a planet from a cloud of dust to a world that can hold oceans, air and life. Read them in order, or jump to the step you are curious about.
Step 1: Gathering the Materials
Every planet starts as dust and gas left over from a newborn star. Here is where the raw materials come from and how grains smaller than smoke particles grow into mountain-sized building blocks.
Step 2 of 7Step 2: Choosing the Orbit
Location decides almost everything about a planet — its temperature, its materials and whether water can stay liquid. Learn how the habitable zone works and why planets do not always stay where they were born.
Step 3 of 7Step 3: Building the Core and Crust
How kilometre-sized rocks grow into a full planet through collisions, melt, and sort themselves into an iron core, a rocky mantle and a thin crust.
Step 4 of 7Step 4: Adding an Atmosphere
Where does a planet's air come from, and why do some planets keep it while others lose it to space? Primary and secondary atmospheres, volcanic outgassing and atmospheric escape explained.
Step 5 of 7Step 5: Bringing Water
Earth formed hot and dry, yet today oceans cover about 71% of its surface. Where did the water come from, and how do oceans and climate keep a planet stable?
Step 6 of 7Step 6: Making It Habitable
Liquid water is only the start. A habitable planet also needs energy, the right chemistry, protection from radiation and a climate that stays stable for billions of years.
Step 7 of 7Step 7: Surviving the Universe
Asteroid impacts, solar storms, runaway climates and a slowly brightening star. The threats every planet faces over its lifetime, and how long a planet like Earth can last.