Saturn

Saturn is the sixth planet from the Sun. It is the second largest planet in the Solar System, after Jupiter. Saturn is a gas giant, and it is about 9 times wider than Earth. It is almost as big as Jupiter, but it has less than a third of Jupiter's mass. Saturn is also very light for its size. It is less dense than water would be, yet it weighs over 95 times as much as Earth.

Saturn is very far from the Sun. It orbits the Sun at a distance of 9.59 AU, which is about 1,434 million km. One trip around the Sun takes it an orbital period of 29.45 years.

Scientists think Saturn has a rocky core at its center. This core is surrounded by a deep layer of metallic hydrogen, a middle layer of liquid hydrogen and liquid helium, and an outer layer of gas. Saturn has a pale yellow color because of ammonia crystals high in its atmosphere. An electrical current in the metallic hydrogen layer is thought to create Saturn's magnetic field. This field is weaker than Earth's, but it is very large because Saturn is so much bigger. Saturn's magnetic field is about a twentieth as strong as Jupiter's. The outer atmosphere is usually plain and has little contrast, though some long-lasting features can appear. Wind speeds on Saturn can reach 1,800 kilometers per hour (1,100 miles per hour).

Saturn has a bright and wide system of rings. They are made mostly of ice particles, with a smaller amount of rocky pieces and dust. At least 293 moons orbit the planet. Of these, 63 have official names. This count does not include the hundreds of moonlets found in the rings.

The largest moon is Titan. It is the second largest moon in the Solar System. Titan is bigger than the planet Mercury, though it has less mass. It is also the only moon in the Solar System with a thick atmosphere.

Name and symbol

Saturn is named after the Roman god of wealth and agriculture. This god was the father of the god Jupiter. Its astronomical symbol can be traced back to the Greek Oxyrhynchus Papyri. In those old writings, the symbol is a Greek kappa-rho joined together, with a horizontal stroke. It is a short form of Κρονος (Cronus), the Greek name for the planet. Later, the symbol began to look like a lower-case Greek eta. In the 16th century, a cross was added at the top to give the symbol a Christian meaning.

The Romans named the seventh day of the week Saturday, which means "Saturn's Day," after the planet Saturn.

Physical characteristics

Saturn is a gas giant, made mostly of hydrogen and helium. It does not have a solid surface. Saturn is the only planet in the Solar System that is less dense than water. It is about 30% less dense. Its average specific density is 0.69 g/cm³, partly because of its atmosphere. Jupiter's mass is 318 times Earth's, while Saturn is only 95 times Earth's. Deep inside Saturn, hydrogen becomes a non-ideal liquid because it is squeezed very tightly. Even deeper down, hydrogen acts like a metal. Saturn's core is similar to Earth's in what it is made of, but it is denser. It is surrounded by a thick, liquid metallic hydrogen layer. The inside of Saturn is very hot, reaching 11,700 °C (21,100 °F) at the core.

The visible features on Saturn move at different speeds depending on how far they are from the equator. Because the planet spins, it is an oblate spheroid. This means it is flattened at the poles and bulging at the equator. Its outer atmosphere is mostly hydrogen, with some helium. Saturn has a simple magnetic dipole field, which is much weaker than Jupiter's. Because of this, its magnetosphere is much smaller than Jupiter's. Like Earth's, Saturn's magnetosphere produces aurorae.

Main article: Magnetosphere of Saturn

Orbit and observation

Saturn is, on average, more than 1.4 billion kilometers (9 AU) from the Sun. It moves around the Sun at about 9.68 km/s. One trip takes 10,759 Earth days, or about 29½ years. Its orbit is tilted 2.48° compared to Earth's orbital plane. Saturn and Jupiter have a near 5:2 mean-motion resonance, which means their orbits are linked in a regular pattern.

Saturn has only one known trojan asteroid, called 2019 UO14, which was announced in September 2024. It sits at the stable L₄ Lagrange point, 60° ahead of the planet. This means only Mercury has no known trojans. Orbital resonance effects, including secular resonance, are thought to explain why so few Saturnian trojans have been found.

Saturn is the most distant of the five planets that can be seen with the naked eye from Earth. The others are Mercury, Venus, Mars, and Jupiter. Uranus, and sometimes 4 Vesta, can also be seen in dark skies. Saturn looks like a bright, yellowish dot of light, with an average apparent magnitude of 0.46. Its brightness changes mostly because the tilt of its rings changes. It is brightest when the rings are tilted most, and faintest when they are tilted least. Saturn takes about 29.4 years to travel around the ecliptic, passing through the background stars of the zodiac. Most people need a telescope or very large binoculars that magnify at least 30 times to see the rings clearly. About every 15 Earth-years, Earth passes through the plane of the rings. The rings then briefly disappear from view because they are so thin. This last happened in 2025, but Saturn was too close to the Sun to be observed.

Saturn is best seen at or near opposition. This is when it is at an elongation of 180° and appears opposite the Sun in the sky. Opposition happens about every 378 days, when Saturn looks brightest. Saturn can also look brighter when its rings are angled so they are easier to see. From time to time, the Moon passes in front of Saturn and blocks it from view. These events happen in "seasons." There are monthly blockings for about 12 months, followed by about five years with none. They only happen when Saturn is near the points where the Moon's orbit crosses its path. This pattern is shaped by Saturn's year and the nodal precession of the Moon's orbit.

Natural satellites

Main article: Moons of Saturn

Saturn has 293 known moons. Of these, 63 have formal names. Many tiny moonlets, between 40 and 500 meters across, are thought to be in Saturn's rings. They are not considered true moons. Titan, the largest moon, makes up more than 90% of the mass orbiting Saturn, including the rings. Saturn's second-largest moon, Rhea, may have a faint ring system of its own and a thin atmosphere. Many of the other moons are small, and 143 of them are less than 50 km across. Most of Saturn's moons are named after Titans from Greek mythology. Titan is the only moon in the Solar System with a thick atmosphere, where complex organic chemistry happens. It is also the only moon with hydrocarbon lakes.

In June 2013, scientists at the IAA-CSIC reported finding polycyclic aromatic hydrocarbons in the upper atmosphere of Titan. These are a possible precursor for life. In June 2014, NASA said it had strong evidence that the nitrogen in Titan's atmosphere came from materials in the Oort cloud. This area is linked to comets. The nitrogen did not come from the materials that formed Saturn long ago. Saturn's moon Enceladus has a chemical makeup similar to comets. It has often been seen as a possible habitat for microbial life. Its salty particles have an "ocean-like" makeup. This suggests that most of the ice it releases comes from liquid salt water evaporating. In 2015, the Cassini spacecraft flew through a plume on Enceladus. It found most of the ingredients needed to support life forms that live by methanogenesis. In April 2014, NASA scientists reported the possible start of a new moon within the A Ring. Cassini had taken an image of this area on 15 April 2013.

Planetary rings

Main article: Rings of Saturn

Saturn is best known for its planetary rings, which make it look unique. The rings reach from about 6,630 to 120,700 kilometers out from Saturn's equator. They are about 20 meters thick on average. They are mostly made of water ice, with small amounts of tholin and about 7% carbon. Their pieces range in size from tiny specks of dust to about 10 meters. Other gas giants have rings too, but Saturn's are the largest and easiest to see.

Scientists do not agree on how old the rings are. One group thinks they are very old. They think the rings formed at the same time as Saturn, from the material that was left over when the planet formed, about 4.6 billion years ago. Some think they formed shortly after the LHB, about 4.1 to 3.8 billion years ago. The other group thinks the rings are much younger, formed about 100 million years ago. A research team from MIT supports the younger idea. They suggested that the rings are what is left of a moon of Saturn that was destroyed. The moon was called "Chrysalis". Some of Saturn's moons, including Pandora and Prometheus, are called shepherd moons. They help keep the rings from spreading out.

History of observation and exploration

Scientists have studied Saturn in three ways. First, people watched it with the naked eye. Then, starting in the 1600s, they used telescopes from Earth. Later, space probes either orbited the planet or made a quick flyby. Today, telescopes on Earth still watch Saturn. Earth-orbiting observatories, such as the Hubble Space Telescope, also study it. The Cassini orbiter studied Saturn too, until its 2017 retirement.

Saturn has been known since ancient times, and it appeared in many early myths. Babylonian astronomers carefully watched and recorded its movements. The ancient Greeks called it Φαίνων Phainon. The Romans called it the "star of Saturn" or the "star of the Sun (i.e. Helios)". In ancient Roman mythology, Phainon was sacred to a farming god, and this is where the planet's modern name comes from. The Romans saw the god Saturnus as the same as the Greek god Cronus. In modern Greek, the planet still has the name Cronus—Κρόνος: Kronos. The Greek scientist Ptolemy calculated Saturn's orbit using observations he made while it was in opposition.

In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn is called "Shani" and is said to judge people by the good and kind deeds they do in life. Ancient Chinese and Japanese cultures called Saturn the "earth star" or "soil star" (土星). This name came from the Five Elements that were used to classify natural things. In Hebrew, Saturn is called Shabbathai. Its angel is Cassiel. Its good spirit is 'Agȋȇl (Hebrew: אגיאל, romanized: ʿAgyal). Its darker spirit is a demon called Zȃzȇl (Hebrew: זאזל, romanized: Zazl). Zazel has been described as a great angel who is called upon in Solomonic magic, where it is said to be "effective in love conjurations". In Ottoman Turkish, Urdu, and Malay, the name Zazel becomes 'Zuhal', which comes from the Arabic language (Arabic: زحل, romanized: Zuhal).

Saturn's rings can only be seen with a telescope of at least 15 mm in diameter. People did not know the rings existed until Christiaan Huygens saw them in 1655 and published his observations in 1659. Galileo used a basic telescope in 1610. He wrongly thought Saturn's not-quite-round look meant it had two moons on its sides. When Huygens used stronger magnification, this idea was proven wrong, and the rings were seen clearly for the first time. Huygens also discovered Saturn's moon Titan. Later, Giovanni Domenico Cassini found four more moons: Iapetus, Rhea, Tethys, and Dione. In 1675, Cassini found the gap now called the Cassini Division. In 1789, William Herschel found two more moons, Mimas and Enceladus. In 1848, a British team found the irregular moon Hyperion, which has a resonance with Titan. In 1899, William Henry Pickering found Phoebe. Phoebe is a very irregular satellite. It takes more than a year to orbit Saturn, moving in a retrograde orbit. In 1944, research on Titan showed that it has a thick atmosphere. This is unusual among the Solar System's moons.

Main article: Exploration of Saturn

Pioneer 11 made the first flyby of Saturn in September 1979. It passed within 20,000 km (12,000 mi) of the cloud tops. It took pictures of the planet and a few moons, but they were too blurry to show detail on the surfaces. It also studied the rings and found the thin F-ring. It showed that dark gaps in the rings look bright when viewed at a high phase angle toward the Sun. This means the gaps contain tiny light-scattering material. It also measured the temperature of Titan.

In November 1980, the Voyager 1 probe visited Saturn. It sent back the first clear images of the planet, its rings, and its moons. Surface features of several moons were seen for the first time. Voyager 1 flew close to Titan and learned more about its atmosphere. This atmosphere blocks visible wavelengths, so no surface details could be seen. The flyby changed the spacecraft's path out of the plane of the Solar System. In August 1981, Voyager 2 continued the study. It took more close-up images of the moons and found signs of changes in the atmosphere and rings. Its camera platform got stuck for a couple of days, so some planned images were lost. Saturn's gravity was used to send it toward Uranus. Together, the two probes found and confirmed several new moons near or inside the rings. They also found the small Maxwell Gap (a gap within the C Ring) and the Keeler gap (a 42 km-wide gap in the A Ring).

Main article: Cassini–Huygens

The Cassini–Huygens space probe entered orbit around Saturn on 1 July 2004. In June 2004, it made a close flyby of Phoebe and sent back clear images and data. Cassini's radar images of Titan showed large lakes with coastlines, islands, and mountains. After two flybys of Titan, the orbiter released the Huygens probe on 25 December 2004. Huygens landed on the surface of Titan on 14 January 2005. Starting in early 2005, scientists used Cassini to track lightning on Saturn. This lightning is about 1,000 times more powerful than lightning on Earth.

In 2006, NASA reported that Cassini had found evidence of liquid water reservoirs. These are no more than tens of meters below the surface of Saturn's moon Enceladus, and they send out geysers. More than 100 geysers have been identified. In May 2011, NASA scientists said that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".

Cassini photographs revealed a new planetary ring. It lies outside the brighter main rings and inside the G and E rings. Scientists think a meteoroid crashing off Janus and Epimetheus may have created it. In July 2006, images showed hydrocarbon lakes near Titan's north pole. Their presence was confirmed in January 2007. In March 2007, hydrocarbon seas were found near the north pole. The largest is almost the size of the Caspian Sea. In October 2006, the probe detected a cyclone-like storm at Saturn's south pole. It was 8,000 km (5,000 mi) wide and had an eyewall. From 2004 to 2 November 2009, the probe discovered and confirmed eight new moons. In April 2013, Cassini sent back images of a hurricane at the north pole. It was 20 times larger than hurricanes on Earth, with winds faster than 530 km/h (330 mph). On 15 September 2017, the spacecraft carried out the "Grand Finale" of its mission. It made a number of passes through gaps between Saturn and its inner rings. The atmospheric entry of Cassini ended the mission.

NASA's Dragonfly mission is the fourth in the New Frontiers program. It is a rotorcraft probe designed to explore Titan and search for signs of the chemical processes that came before life. NASA chose the mission in 2019. As of 2025, it is scheduled to launch in July 2028, with a total cost of $3.35 billion. It would arrive at Titan in 2034. By April 2025, the mission had passed its Critical Design Review. It is planned to launch on a SpaceX Falcon Heavy rocket from Kennedy Space Center.

In fiction

Saturn has appeared in stories since at least 1752, when Voltaire published his novel Micromégas. Early stories often showed it as a solid planet. Later, people learned that Saturn is a gas planet.

Saturn's moons also appear in stories, especially Titan.