Saturn is the sixth planet from the Sun and the second-largest planet in the solar system after Jupiter. It is a gas giant composed mainly of hydrogen and helium, with no solid surface beneath its deep atmosphere. Although Jupiter, Uranus and Neptune also have rings, Saturn’s are by far the brightest and most visually prominent. Together with the planet’s enormous family of moons, they form a complex planetary system that was explored most closely by NASA’s Cassini spacecraft.
What Is Saturn?
Saturn is one of the four giant planets in the outer solar system. It orbits beyond Jupiter at an average distance of about 1.43 billion kilometers (886 million miles) from the Sun. The planet is best known for the broad ring system encircling its equator. Saturn also has hundreds of moons, ranging from tiny bodies embedded within the rings to Titan, which is larger in diameter than the planet Mercury.
Saturn Quick Facts
| Planet type | Gas giant |
|---|---|
| Position from the Sun | Sixth planet |
| Equatorial diameter | 120,536 km (74,898 miles) |
| Average distance from the Sun | 1.43 billion km (886 million miles) |
| Length of day | About 10 hours 33 minutes |
| Length of year | 29.45 Earth years |
| Average cloud-top temperature | About −140°C (−220°F) |
| Known moons | 293 |
| Main ring groups | Seven |
| Surface gravity | About 1.07 times Earth’s gravity |
| Current spacecraft | None |
The Second-Largest Planet in the Solar System
Saturn has an equatorial diameter of about 120,536 kilometers (74,898 miles), making it more than nine times wider than Earth. Around 760 Earths could fit inside its volume, although Saturn contains only about 95 times Earth’s mass. This difference results from Saturn’s extremely low density. Its average density is approximately 0.69 grams per cubic centimeter, making it the only planet less dense than water. Saturn would therefore float if it could be placed in a sufficiently large ocean, although no such ocean could exist in practice.
A Gas Giant With No Solid Surface
Saturn consists predominantly of hydrogen and helium and has no solid surface on which a spacecraft could land. Its atmospheric gases gradually become denser, hotter and more compressed with increasing depth.
Deeper inside the planet, hydrogen changes into a liquid and then into metallic hydrogen, a form capable of conducting electricity. Near the center is a dense mixture of rock, ice and metals. Measurements made by Cassini suggest that this core may be diffuse, with its heavier material mixed into the surrounding layers rather than confined within a sharply defined solid sphere. A spacecraft descending into Saturn would therefore encounter steadily increasing pressure and temperature until it was crushed and destroyed long before reaching the deep interior.
Saturn’s Atmosphere, Weather and North-Polar Hexagon
Saturn’s atmosphere is composed mainly of hydrogen and helium, with much smaller quantities of methane, ammonia and other compounds. Ammonia ice forms its upper clouds, while hazes above them help give the planet its muted yellow and gold appearance.
Winds near Saturn’s equator can exceed 1,600 kilometers per hour (1,000 mph). The planet also occasionally develops enormous storms known as Great White Spots. These appear roughly once during each Saturnian year, although their exact timing and behavior vary.
One of Saturn’s most remarkable atmospheric features is the six-sided jet stream surrounding its north pole. Known as the north-polar hexagon, it is wider than Earth and has persisted for decades. It is not a solid structure but a vast atmospheric wave maintained by powerful winds flowing around the pole.
Credit: NASA/JPL-Caltech/Space Science Institute/Val Klavans
The Most Spectacular Ring System in the Solar System
Saturn’s rings consist primarily of water ice mixed with smaller amounts of rock and dust. Individual particles range from microscopic grains to objects as large as houses, with some potentially reaching the size of mountains.
The main ring system spans approximately 280,000 kilometers (175,000 miles) from edge to edge, yet many parts are only tens of meters thick. This combination of enormous width and extraordinary thinness gives the rings their delicate appearance.
The brightest sections are called the A, B and C rings. The Cassini Division, a region with fewer ring particles, separates the A and B rings. Several fainter rings extend beyond the main system.
Small shepherd moons and gravitational resonances with larger moons help shape gaps, waves and sharply defined edges within the rings. Their exact origin and age remain uncertain, although they may contain material from icy moons or other bodies that broke apart after approaching Saturn.
Saturn’s 293 Moons
Saturn has 293 confirmed moons, more than any other planet. Most are small, irregular objects, but several rank among the solar system’s most scientifically important worlds.
Titan, Saturn’s largest moon, is wider than Mercury and is the only moon known to possess a dense atmosphere. Its surface contains rivers, lakes and seas filled with liquid methane and ethane, while evidence indicates that an ocean of liquid water lies beneath its icy crust.
Enceladus also appears to contain a global subsurface ocean. Geysers near its south pole spray water vapor, ice grains and organic compounds into space, supplying material to Saturn’s E ring.
Other major moons include Rhea, Iapetus, Dione, Tethys and Mimas. Each has its own distinctive surface, ranging from the enormous equatorial ridge of Iapetus to the giant Herschel impact crater on Mimas.
A Short Day but a Long Year
Saturn completes one rotation in approximately 10 hours and 33 minutes, giving it the second-shortest day of any planet after Jupiter. This rapid rotation causes the planet to bulge visibly around its equator and flatten at the poles. Measuring Saturn’s rotation is difficult because its atmosphere has no permanent surface markings and different cloud bands rotate at different speeds. Scientists estimate the rotation of its deep interior using changes in its magnetic field and waves detected within the rings.
Despite its short day, Saturn requires about 29.45 Earth years to complete one orbit around the Sun. Its axis is tilted by approximately 26.7 degrees, producing seasons similar in principle to Earth’s, although each Saturnian season lasts for more than seven Earth years.
Saturn’s Magnetic Field and Auroras
Electrical currents within Saturn’s layer of metallic hydrogen generate a powerful magnetic field. This produces an enormous magnetosphere that surrounds the planet and interacts with the solar wind, the rings and material released by its moons.
Saturn’s magnetic and rotational axes are aligned unusually closely. This near-perfect alignment makes its exact rotation rate more difficult to determine than that of most other planets.
Auroras occur around both poles as charged particles travel along magnetic-field lines and enter the upper atmosphere. They have been observed mainly at ultraviolet and infrared wavelengths and are influenced by both the solar wind and material within Saturn’s moon system.
Spacecraft Exploration of Saturn
Four spacecraft have visited Saturn. Pioneer 11 completed the first flyby in 1979, followed by Voyager 1 in 1980 and Voyager 2 in 1981. These missions returned the first detailed close-range views of the planet, its rings and many of its moons.
The Cassini spacecraft entered orbit around Saturn in 2004 and studied the system until 2017. Its discoveries included active geysers on Enceladus, hydrocarbon lakes on Titan, complex structures within the rings and seasonal changes in Saturn’s atmosphere. Cassini carried the European Space Agency’s Huygens probe, which landed on Titan in January 2005. It remains the first and only spacecraft to land in the outer solar system.
No spacecraft is currently operating at Saturn. NASA’s Dragonfly mission is expected to launch no earlier than July 2028 and reach Titan in late 2034. The rotorcraft will travel between locations on the moon’s surface to investigate its chemistry and potential habitability.
How to Find and Observe Saturn
Saturn is visible without optical aid and usually resembles a steady, pale-yellow star along the zodiac. Because it takes nearly 30 years to orbit the Sun, it moves slowly against the background stars and can remain within the same zodiac constellation for more than two years. The best observing period is around opposition, when Saturn is closest to Earth, appears brightest and remains visible for most of the night.
Binoculars show Saturn as a bright point and may reveal Titan nearby under sufficiently dark conditions. High-powered, steadily mounted binoculars can sometimes make the planet appear slightly elongated because of its rings.
A small telescope with an aperture of around 60 millimeters can reveal the rings clearly. An 80- to 100-millimeter telescope may also show Titan, the shadow of the rings on the planet and, under good atmospheric conditions, the dark Cassini Division.
The apparent tilt of the rings changes as Saturn and Earth orbit the Sun. They can open widely toward Earth or become almost edge-on, when the exceptionally thin rings may become difficult to see through a small telescope.
Who Discovered Saturn?
Saturn is visible without a telescope and has therefore been known since ancient times. Babylonian astronomers recorded its movements, while early skywatchers recognized it as the faintest and slowest-moving of the five planets visible to the unaided eye.
Galileo Galilei became the first person known to observe Saturn through a telescope in 1610. His instrument could not resolve the rings clearly, causing him to describe the planet as having two companion bodies or handles.
Christiaan Huygens identified the structure as a ring surrounding Saturn in 1655. That same year, he discovered Titan. Giovanni Domenico Cassini later discovered several additional moons and identified the prominent gap between the A and B rings now called the Cassini Division.
Why Saturn Is Named After a Roman God
The Romans named the planet after Saturn, their god of agriculture and wealth. Saturn was identified with the Greek Titan Cronus, who ruled the gods before being overthrown by his son Zeus. The Romans knew Zeus as Jupiter, making the god Saturn the mythological father of the god after whom Jupiter was named.
Saturn’s influence remains embedded in the modern calendar: Saturday derives from the Latin dies Saturni, meaning “day of Saturn.” It is the only English day of the week still named directly after a Roman god.