Equatorial Radius of Saturn

Saturn's radius, like Jupiter's, is quoted where the atmosphere reaches one bar — a gas giant offers no other surface to measure. The value comes from Voyager and Cassini radio occultations, timing spacecraft signals as they sliced through the atmosphere. The disc is the second largest of any planet, yet it is the appendage that defines the view: the main rings span 270 000 km edge to edge, four and a half times the planet's own diameter, while being locally perhaps ten metres thick — proportionally thinner than a sheet of paper the size of a city.

Radius cubed against mass gives Saturn's famous distinction: a mean density of 687 kg/m³, the only planet lighter than water. The interior that fills this volume is hydrogen and helium over a heavy-element core, and Cassini's final orbits found the core "fuzzy" — diffuse and extended like Jupiter's, its oscillations readable as spiral waves it drives in the rings.