Saturn is the sixth planet from the sun and the second largest planet in the solar system. 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.
Saturn was the Roman name for Cronus, the lord of the Titans in Greek mythology. Saturn is the root of the English word “Saturday.”
Physical characteristics of Saturn
Saturn is a gas giant made up mostly of hydrogen and helium. Saturn is bigenough 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.
Saturn is the farthest planet from Earth visible to the naked human eye. 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 kph) 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 km) wider at its equator than between the poles.
Saturn’s most 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.
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
Saturn has a magnetic field about 578 times more powerful than Earth’s.
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.
Saturn seems to have a core between about 10 to 20 times as massive as the 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. 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.
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, and Enceladus shows evidence of “ice volcanism,” spewing out water and other chemicals. A number of these satellites, such as Prometheus and Pandora, are shepherd moons, interacting with ring material to keep rings in their orbits.
Galileo Galilei was the first to see Saturn’s rings in 1610, although from his telescope they resembled handles or arms. It took Dutch astronomerChristiaan Huygens, who had a more powerful telescope, to propose that Saturn had a thin, flat ring.
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 ringspans up to 200 times the diameter of the planet. The rings are believe to be debris left over from comets, asteroids or shattered moons. 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.
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 now in orbit around Saturn is 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.
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 helpedviolently 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.
- How Big is Saturn?
- How Far Away is Saturn?
- Saturn’s Atmosphere
- What is Saturn Made Of?
- How Was Saturn Formed?
- What is the Temperature of Saturn?
The Ringed Planet
Saturn was the most distant of the five planets known to the ancients. In 1610, Italian astronomer Galileo Galilei was the first to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet. He sketched them as separate spheres and wrote that Saturn appeared to be triple-bodied. In 1659, Dutch astronomer Christiaan Huygens, using a more powerful telescope than Galileo’s, proposed that Saturn was surrounded by a thin, flat ring.
In 1675, Italian-born astronomer Jean-Dominique Cassini discovered a “division” between what are now called the A and B rings. It is now known that the gravitational influence of Saturn’s moon Mimas is responsible for theCassini Division, which is 3,000 miles (4,800 kilometers) wide.
Like Jupiter, Saturn is made mostly of hydrogen and helium. Its volume is 755 times greater than that of Earth. Winds in the upper atmosphere reach 1,600 feet (500 meters) per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 360 feet, or 110 meters, per second.) These superfast winds, combined with heat rising from within the planet’s interior, cause the yellow and gold bands visible in the atmosphere.
Saturn’s ring system is the most extensive and complex in the solar system, extending hundreds of thousands of kilometers from the planet. In the early 1980s, NASA’s two Voyager spacecraft revealed that Saturn’s rings are made mostly of water ice. They also found “braided” rings, ringlets, and “spokes,” dark features in the rings that circle the planet at different rates from that of the surrounding ring material. Material in the rings ranges in size from a few micrometers to several tens of meters. Two of Saturn’s small moons orbit within gaps in the main rings.
Saturn has 52 known natural satellites, or moons, and there are probably many more waiting to be discovered. Saturn’s largest satellite, Titan, is a bit bigger than the planet Mercury. (Titan is the second-largest moon in the solar system; only Jupiter’s moon Ganymede is bigger.) Titan is shrouded in a thick, nitrogen-rich atmosphere that might be similar to what Earth’s was like long ago. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth. Saturn also has many smaller “icy” satellites. From Enceladus, which shows evidence of recent (and ongoing) surface changes, to Iapetus, with one hemisphere darker than asphalt and the other as bright as snow, each of Saturn’s satellites is unique.
Though Saturn’s magnetic field is not as huge as Jupiter’s, it is still 578 times as powerful as Earth’s. Saturn, the rings, and many of the satellites lie totally within Saturn’s enormous magnetosphere, the region of space in which the behavior of electrically charged particles is influenced more by Saturn’s magnetic field than by the solar wind. Hubble Space Telescope images show that Saturn’s polar regions have aurorae similar to Earth’s. Aurorae occur when charged particles spiral into a planet’s atmosphere along magnetic field lines.
Voyagers 1 and 2 flew by and photographed Saturn in 1981. The next chapter in our knowledge of Saturn is under way, as the Cassini- Huygens spacecraft continues its exploration of the Saturn system. The Huygens probe descended through Titan’s atmosphere in January 2005, collecting data on the atmosphere and surface. Cassini will orbit Saturn more than 70 times during a four-year study of the planet and its moons, rings, and magnetosphere. Cassini-Huygens is sponsored by NASA, the European Space Agency, and the Italian Space Agency.
—Text courtesy NASA/JPL