Saturn is the sixth planet from the sun and the second largest planet in the solar system. Saturn was the Roman name for Cronus, the lord of the Titans in Greek mythology. Saturn is the root of the English word "Saturday."
Saturn is the farthest planet from Earth visible to the naked human eye, but it is through a telescope that the planet's most outstanding features can be seen: Saturn's rings. Although the other gas giants in the solar system — Jupiter, Uranus and Neptune — also have rings, those of Saturn are without a doubt the most extraordinary.
Physical characteristics of Saturn
Saturn is a gas giant made up mostly of hydrogen and helium. Saturn is big enough to hold more than 760 Earths, and is more massive than any other planet except Jupiter, roughly 95 times Earth's mass. However, Saturn has the lowest density of all the planets, and is the only one less dense than water — if there were a bathtub big enough to hold it, Saturn would float.
The yellow and gold bands seen in Saturn's atmosphere are the result of super-fast winds in the upper atmosphere, which can reach up to 1,100 mph (1,800 km/h) around its equator, combined with heat rising from the planet's interior.
Saturn spins faster than any other planet except Jupiter, completing a rotation roughly every 10-and-a-half hours. This rapid spinning causes Saturn to bulge at its equator and flatten at its poles — the planet is 8,000 miles (13,000 kilometers) wider at its equator than between the poles.
A recent curiosity may be the giant hexagon circling its north pole, with each of its sides nearly 7,500 miles (12,500 km) across — big enough to fit nearly four Earths inside. Thermal images show it reaches some 60 miles (100 km) down into the planet's atmosphere. It remains uncertain what causes it, although one study suggested that shallow jets in the atmosphere may be responsible for its formation.
Other titanic storms appear in Saturn's atmosphere once every Saturn year (approximately 30 Earth-years), disrupting the temperature and winds of the planet's skies. Six such storms have been observed on the planet since 1876, but in 2011, NASA's Cassini spacecraft became the first orbiter to observe one.
In 2015, researchers suggested that there is a gap between these storms because of the presence of water vapor in Saturn's atmosphere. The moisture stops warm air from rising in the short term, but in the long term, Saturn's upper atmosphere becomes dense, sinks and creates a huge storm.
Like other giant planets, Saturn also has northern and southern lights, caused by particles from the sun.
Here are some of Saturn's parameters, according to NASA:
Composition & structure
Atmospheric composition (by volume): 96.3 percent molecular hydrogen, 3.25 percent helium, minor amounts of methane, ammonia, hydrogen deuteride, ethane, ammonia ice aerosols, water ice aerosols, ammonia hydrosulfide aerosols
Magnetic field: Saturn has a magnetic field about 578 times more powerful than Earth's.
Chemical composition: Saturn seems to have a hot solid inner core of iron and rocky material surrounded by an outer core probably composed of ammonia, methane, and water. Next is a layer of highly compressed, liquid metallic hydrogen, followed by a region of viscous hydrogen and helium. This hydrogen and helium becomes gaseous near the planet's surface and merges with its atmosphere.
Internal structure: Saturn seems to have a core between about 10 to 20 times as massive as Earth.
Orbit & rotation
Average distance from the sun: 885,904,700 miles (1,426,725,400 km). By comparison: 9.53707 times that of Earth.
Perihelion (closest approach to sun): 838,519,000 miles (1,349,467,000 km). By comparison: 9.177 times that of Earth.
Aphelion (farthest distance from sun): 934,530,000 miles (1,503,983,000 km). By comparison: 9.886 times that of Earth.
Saturn has at least 62 moons. Since the planet was named after Cronus, lord of the Titans in Greek mythology, most of Saturn's moons are named after other Titans, their descendants, as well as after giants from Gallic, Inuit and Norse myths.
Saturn's largest moon, Titan, is slightly larger than Mercury, and is the second-largest moon in the solar system behind Jupiter's moon Ganymede. (Earth's moon is the fifth largest.) Titan is veiled under a very thick, nitrogen-rich atmosphere that might be like what Earth's was long ago, before life. While the Earth's atmosphere extends only about 37 miles (60 km) into space, Titan's reaches nearly 10 times as far. The atmosphere contains a number of hydrocarbons, chemicals that primarily make up fossil fuels on Earth. Methane rain falls from the sky and moves through the moon’s icy crust. A study detected propylene, a chemical used to make plastics, in the planet's atmosphere. Observations released in 2016 show that Titan has surprisingly deep canyons flooded with liquid hydrocarbons.
These moons can possess bizarre features. Pan and Atlas are shaped like flying saucers; Iapetus has one side as bright as snow and one side as dark as coal. Enceladus shows evidence of "ice volcanism," and a hidden ocean spewing out water and other chemicals from the 101 geysers spotted at the moon's southern pole. A number of these satellites, such as Prometheus and Pandora, are shepherd moons, interacting with ring material to keep rings in their orbits.
Though scientists have identified many moons, the chaotic system has other small moons constantly being created and destroyed.
Galileo Galilei was the first to see Saturn's rings in 1610, although from his telescope they resembled handles or arms. It took Dutch astronomer Christiaan Huygens, who had a more powerful telescope, to propose that Saturn had a thin, flat ring.
Astronomers with even more powerful telescopes discovered that Saturn actually has many rings made of billions of particles of ice and rock, ranging in size from a grain of sugar to the size of a house. The largest ring spans up to 7,000 times the diameter of the planet. The rings are believed to be debris left over from comets, asteroids or shattered moons. (A 2016 study also suggested the rings may be the carcasses of dwarf planets.) Although they extend thousands of miles from the planet, the main rings are typically only about 30 feet thick. The Cassini-Huygens spacecraft revealed vertical formations in some of the rings, with particles piling up in bumps and ridges more than 2 miles (3 km) high.
The rings are generally named alphabetically in the order they were discovered. They are usually relatively close to each other, with one key exception caused by the Cassini Division, a gap some 2,920 miles (4,700 km) wide. The main rings, working out from the planet, are known as C, B and A, with the Cassini Division separating B and A. The innermost is the extremely faint D ring, while the outermost to date, revealed in 2009, could fit a billion Earths within it.
Mysterious spokes have been seen in Saturn's rings, which might form and disperse over a few hours. Scientists have conjectured these spokes might be composed of electrically charged sheets of dust-sized particles created by small meteors impacting the rings or electron beams from the planet's lightning. Saturn's F Ring also has a curious braided appearance — it is composed of several narrow rings, and bends, kinks, and bright clumps in them can give the illusion that these strands are braided. Changes in the rings of Saturn, as well as the rings of Jupiter, are caused by impacts from asteroids and comets.
Late in its mission, the Cassini spacecraft had its orbit altered in a way that put it closer to the rings than any other spacecraft. While data was still being analyzed as of late 2017, the spacecraft did get a closer look at clumping particle structures called "straw," and features called "propellers," which could yield more information about the rings' formation.
Saturn's gravitational impact on the solar system
As the most massive planet in the solar system after Jupiter, the pull of Saturn's gravity has helped shape the fate of our system. It may have helped violently hurl Neptune and Uranus outward. It, along with Jupiter, might also have slung a barrage of debris toward the inner planets early in the system's history.
Scientists are still learning about how gas giants in general form, and sometimes run models on early solar system formation to understand the role that Jupiter, Saturn and other planets play in our solar system. A 2017 study suggests that Saturn — more so than Jupiter — steers dangerous asteroids away from Earth.
Research & exploration
The first spacecraft to reach Saturn was Pioneer 11 in 1979, flying within 13,700 miles (22,000 km) of it, which discovered the planet's two of its outer rings as well as the presence of a strong magnetic field. The Voyager spacecraft discovered the planet's rings are made up of ringlets, and sent back data that led to the discovery or confirmation of the existence of nine moons.
The Cassini spacecraft, a Saturn orbiter, was the largest interplanetary spacecraft ever built, a two-story-tall probe that, at 6 tons in weight (5,650 kilograms), is roughly equal in mass to an empty 30-passenger school bus. It discovered plumes on the icy moon Enceladus, and carried the Huygens probe, which plunged through Titan's atmosphere to successfully land on its surface. After a decade of observation, Cassini returned incredible data about the planet and its moons, as well as a photo recreating the original “Pale Blue Dot” image, which captures Earth from behind Saturn, in 2013. The mission concluded in September 2017 when Cassini, low on fuel, was deliberately directed into Saturn to avoid the slight chance of contaminating a habitable moon.
While there are no future missions definitely planned for Saturn, there are several ideas for sending spacecraft in that general direction. This includes missions to probe the icy moon Enceladus or Titan. The method of probing the moons is still being figured out, with some people suggesting submarines and others suggesting modified rovers.
Additional reporting by Elizabeth Howell and Nola Taylor Redd, Space.com Contributors