The Planets
Eight real planets, eight finished construction projects. Each page looks at how the planet was built, what went right, and what went wrong.
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.
Planet 2 · Earth's overheated twinVenus
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.
Planet 3 · The reference buildEarth
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.
Planet 4 · The planet that dried outMars
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.
Planet 5 · The first giantJupiter
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.
Planet 6 · The ringed giantSaturn
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.
Planet 7 · The sideways ice giantUranus
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.
Planet 8 · The windy edgeNeptune
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.