Saturn’s rings are made of countless chunks of nearly pure water ice - from dust grains to house-sized boulders - spanning 280,000 km yet averaging only about 10 metres thick. The planet itself is so light for its size that it would float in a big enough ocean.
With 285 known moons, Saturn has more than every other planet combined.
Its average density is less than water’s.
The rings may be young - perhaps only a few hundred million years old.
Rings are rubble, not solid
Every ring particle is a tiny moon on its own orbit. Inner particles orbit faster than outer ones, and small shepherd moons sculpt the gaps - the rings are gravity made visible.
Physical characteristics
Diameter
120,536 km
Mass
5.680e+26 kg
Surface gravity
9 m/s²
Density
0.69 g/cm³
Rotation period
10.66 h
Axial tilt
26.7°
Mean temperature
-140 °C
Geometric albedo
0.5
Known moons
274
Atmosphere and composition
Atmosphere
About 96% H₂ and 3% He with traces of methane and ammonia, veiled by a high haze that softens its bands.
Composition
Hydrogen and helium around a rocky-icy core; the whole planet averages less dense than water.
Interior structure
Dilute coremodelled
Rock and ice mixed through hydrogen across 60% of the radius.
Metallic hydrogenmodelled
A conducting layer that generates the strikingly axis-aligned magnetic field.
Molecular hydrogen envelopemodelled
The least dense planet - it would float, if you could find the bathtub.
How we know: Cassini’s final orbits measured the gravity field, and waves in Saturn’s own rings act as a natural seismometer - both point to a huge fuzzy core.
Missions
Voyager 2NASA · Flyby probe · 1977 · active
Launched 16 days before its twin, Voyager 2 is the only spacecraft ever to visit all four giant planets - Jupiter, Saturn, Uranus and Neptune. It entered interstellar space in 2018 and is still returning data.
Voyager 1NASA · Flyby probe · 1977 · active
The most distant human-made object, now roughly 25 billion km from the Sun. After historic flybys of Jupiter, Saturn and Titan, Voyager 1 became the first spacecraft to enter interstellar space in 2012.
Cassini orbited Saturn for 13 years, delivering ESA’s Huygens probe to the surface of Titan in January 2005 - the first landing in the outer Solar System. It ended with a deliberate plunge into Saturn in 2017 to protect the potentially habitable moons Enceladus and Titan.