Saturn

Saturn, the sixth planet from the Sun, is famous for its beautiful rings. The second-largest planet after Jupiter, this gas giant has an average density lower than water and more than 270 moons.

What kind of planet is it?

Saturn is the sixth planet, orbiting at an average distance of about 9.55 AU from the Sun roughly once every 29.5 years. Its equatorial diameter is about 120,536 km, more than nine times Earth's, making it second in size only to Jupiter. It's the most distant planet visible to the naked eye, so until the telescope was invented it was the outermost planet people knew.

Like Jupiter, Saturn is a gas giant made mostly of hydrogen and helium. Deep inside there's thought to be a layer of metallic hydrogen, with a core of rock and ice at the center. Despite its huge size, its average density is only about 0.69 g/cm³, lower than water. Saturn is the only planet in the Solar System less dense than water.

Saturn spins fast, completing a rotation in about 10.7 hours. This makes its equator bulge, giving it the most flattened shape of any planet. With no solid surface, its exact rotation period is also tricky to measure. Its axis is tilted about 26.73°, so it has seasons like Earth, and as Saturn orbits, the angle at which we see its rings from Earth gradually changes. Gravity at the cloud tops is about 1.07 times Earth's, close to our own.

Atmosphere and weather

The average temperature at Saturn's cloud tops is about -140°C (-220°F). Like Jupiter it has banded clouds, but a thin layer of haze on top makes the patterns softer and a pale yellow. Near the equator, winds blow at well over 1,500 km/h.

At Saturn's north pole sits a curious hexagon: a giant six-sided jet stream with each side longer than Earth's diameter. It was first discovered by the Voyager spacecraft in the 1980s and studied in detail by Cassini, and a huge swirling storm sits at its center.

Roughly once every Saturnian year, a giant white storm called a Great White Spot appears. In 2010–2011, Cassini watched one grow so large it wrapped all the way around the northern hemisphere. Like Jupiter, Saturn gives off more energy from its interior than it receives from the Sun.

Moons and rings

Saturn's rings are made of countless pieces of ice, large and small, with a bit of rocky debris. The particles range from dust-sized grains to chunks as big as a house. The main rings spread about 270,000 km across, yet most of them are extremely thin, from tens of meters to around 1 km thick. The rings are named with letters like A, B and C in order of discovery, and between the A and B rings lies a wide gap called the Cassini Division.

As of 2025, Saturn has more than 270 known moons, the most of any planet in the Solar System. Most are small bodies a few kilometers across. The major moons include:

• Titan: About 5,150 km across, the second-largest moon in the Solar System. It's the only moon with a thick atmosphere, and its surface has lakes and seas of liquid methane and ethane.
• Enceladus: A small icy moon about 500 km across that shoots plumes of water into space from cracks near its south pole. These are considered evidence of an ocean beneath the ice.
• Mimas: It has one enormous crater for its size, which is why people say it looks like the Death Star from Star Wars.
• Iapetus: A two-faced moon, with one hemisphere dark and the other bright.
• There are also medium-sized icy moons such as Rhea, Dione and Tethys.

Exploration

The first person to see Saturn's rings was Galileo in 1610, but his telescope wasn't powerful enough, so he described something like ears attached to either side of the planet. In the 1650s, Christiaan Huygens worked out that it was a ring surrounding the planet. Huygens also discovered Titan in 1655.

• Pioneer 11 (USA, 1979): The first spacecraft to fly past and observe Saturn.
• Voyager 1 (1980) and Voyager 2 (1981): Revealed the complex structure of the rings and the faces of many moons in detail. Voyager 1 observed Titan up close.
• Cassini-Huygens (USA/Europe/Italy, launched 1997): Entered Saturn orbit in 2004 and studied Saturn, its rings and its moons for 13 years. Its companion, the Huygens probe, landed on Titan in January 2005, becoming the first spacecraft to land on a body in the outer Solar System. Cassini discovered Enceladus's plumes and Titan's lakes, and ended its mission in September 2017 by plunging into Saturn's atmosphere.

Next up, NASA's Dragonfly is set to fly through Titan's skies to explore it.

Fun facts

• If you had a bathtub big enough to hold Saturn, it would float, since its average density is lower than water.
• About every 13 to 16 years, Earth passes through the plane of Saturn's rings. We then see the rings edge-on and they almost seem to vanish. The most recent time was in 2025.
• Some research suggests Saturn's rings may be much younger than the planet itself, but the debate is still going on.
• Some of the gaps and edges in the rings are sculpted and kept in shape by the gravity of small shepherd moons.
• Saturn is named after the Roman god Saturn. In Korean, Chinese and Japanese, its name means “earth star,” after the earth element of the five traditional elements (wood, fire, earth, metal and water).

See it in Planetica

In Solar System view, Saturn appears on the sixth orbit, beyond Jupiter. Its position is its real location for today's date, calculated from J2000 orbital elements, but since one orbit takes about 29.5 years, it creeps along very slowly.

Pick Saturn and fly in close to see the rings around the planet. Change your viewpoint to admire them from different angles. Moons approximating the real ones circle around it, drawn larger than their true proportions so they're easy to see.

Size, gravity, day length, axial tilt, average temperature and orbital period are based on real values. However, the surface patterns are created by Planetica's planet generator, so they don't reproduce Saturn's real bands or the hexagon at its north pole.

Other planets

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• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune