A planet builder's handbook
How to build a planet in space
Gather dust, pick an orbit, grow a core, wrap it in air, add an ocean — and keep it alive. Nature has done this billions of times. Here is how it works, one step at a time.
The seven steps
Learn from finished planets
Our solar system is a showroom of eight very different builds. Some kept their oceans, some lost their air, one is still glowing from the heat of its own formation.
Mercury
The smallest planet and the closest to the Sun, Mercury is mostly iron core with a thin rocky shell. How it was built, why it has almost no atmosphere, and why there is ice near its poles.
Venus
Venus is almost the same size as Earth but has a crushing carbon dioxide atmosphere and a surface hot enough to melt lead. A case study in how a planet build can go wrong.
Earth
The only planet known to host life. What makes Earth work — oceans, plate tectonics, a magnetic field, a large moon and a stable climate — and how they fit together.
Mars
Mars once had rivers, lakes and a thicker atmosphere. Today it is a cold desert. How Mars was built, what it lost and why it remains the top target in the search for past life.
Jupiter
Jupiter holds more than twice the mass of all the other planets combined. How a gas giant is built, what lies beneath its clouds, and how it shaped the rest of the solar system.
Saturn
Saturn is light enough to float in a giant bathtub and wears the most spectacular rings in the solar system. How it formed, what its rings are made of, and why its moons Titan and Enceladus matter.
Uranus
Uranus spins on its side, giving it the most extreme seasons in the solar system. What an ice giant is made of, how Uranus may have been knocked over, and why we know so little about it.
Neptune
The farthest planet from the Sun, Neptune was found by mathematics before anyone saw it. Supersonic winds, a captured moon and clues that the giant planets moved after they formed.
Tools for planet builders
Design Your Planet
Pick an orbit, a climate and how much land you want, then sculpt your own planet tile by tile in 3D.
Open tool →Your Weight and Age on Other Planets
How much would you weigh on Mars? How old would you be on Jupiter? Enter your numbers and find out.
Open tool →Planet Size Comparison
See the Sun, the planets and the Moon side by side at true relative scale.
Open tool →Habitable Zone Calculator
Choose a star and find the range of distances where a planet could keep liquid water on its surface.
Open tool →What if…?
What If Earth Had Rings?
Imagine Saturn-style rings circling Earth. How they would look from different latitudes, how they would change our climate, and why they would make spaceflight much harder.
What If Earth Had Two Suns?
Planets with two suns are real. How orbits work around a pair of stars, what double sunsets and double shadows would be like, and whether such worlds can be habitable.
What If the Moon Disappeared?
No more moonlight, smaller tides, and a planet whose tilt could wander over millions of years. What Earth would be like without its Moon — and what the Moon has already done for us.
What If Earth Were Twice as Big?
A planet with twice Earth's diameter would be a super-Earth with stronger gravity, a heavier atmosphere and very different conditions for life — and for anyone trying to launch a rocket.
What If Earth Stopped Spinning?
A sudden stop would be catastrophic. A slow stop would give us six months of daylight, six months of night, and oceans that drain toward the poles. Here is what would happen.