Saturn

Saturn is the sixth planet from the Sun and the second largest, best known for its bright, wide system of rings made of countless pieces of ice and rock. The rings span up to about 280,000 kilometres yet are only tens of metres thick.

A gas giant like Jupiter, Saturn is so low in density it would float in water. It has well over a hundred confirmed moons, including Titan — the only moon with a thick atmosphere and lakes of liquid methane.

The numbers above show how that low density works out. Saturn carries 95.2 Earth masses, but its radius of 58,232 km is more than nine times ours, which means the same material is spread through a volume roughly 760 times Earth’s. The result is a planet less dense than water, and a surface gravity at the cloud tops of just 10.44 m/s² — barely more than you feel standing at home, despite Saturn being ninety-five times heavier.

A day lasts 10.7 hours, fast enough to bulge the planet noticeably at its equator, while a year takes about 29 Earth years from 9.537 AU out. At that distance sunlight is about one per cent of what Earth receives and the mean temperature reads −139 °C. With 146 confirmed moons, Saturn is less a single planet than a small system in its own right — and the rings, only tens of metres thick but hundreds of thousands of kilometres across, are the flattest structure in the solar system. See it in context in the 3D solar system simulator.