Named for the Roman god of agriculture, Saturn was the most distant planet known by ancient astronomers. Centuries later, we are still unraveling the planet’s many mysteries.

As one of the gas giants, Saturn is believed to be a huge ball of gas with no solid surface. Its inner core is thought to be hot, consisting of iron and rock and surrounded by an outer core made of ammonia, methane, and water. Surrounding this outer core is a layer of compressed liquid metallic hydrogen, above which is an area containing hydrogen and helium. The hydrogen and helium mixture is syrupy, turning gaseous near Saturn’s surface, where it becomes part of the planet’s atmosphere. The planet is covered by a thick layer of clouds, which recent photographs have shown to be much more diverse than previously thought. Those deep within the atmosphere come in several shapes and sizes, unlike the more even layer of clouds found in the upper atmosphere.

Saturn’s orbit around the Sun lasts 29.5 Earth years, and it spins on its axis once every 10 hours and 39 minutes. Only Jupiter rotates faster than Saturn. Because Saturn tilts on its axis, the northern and southern hemispheres are unheated unequally by the Sun. Saturn’s volume is 755 times greater than Earth’s. And, with a mass 95 times that of Earth, it is the most massive planet after Jupiter. However, it has the lowest density of any planet in the solar system, and is about one-tenth the density of Earth. The pressure on Saturn is so extreme it can turn gas into liquid.

Saturn has 46 natural satellites. Four of them -- Pan, Atlas, Prometheus, and Pandora -- are called shepherd moons, because they “herd” particles orbiting Saturn into the planet’s ring system. Saturn’s satellites are some of the most intriguing bodies in our solar system. Titan is the second-largest moon in the solar system, after Jupiter’s Ganymede, and is bigger than Mercury and Pluto. It is the only moon with a dense atmosphere, and many scientists believe Titan’s atmosphere may be similar to Earth’s early atmosphere. Several other moons have startling properties: Iapetus is 10 times brighter on one half than on the other, Mimas has a crater that spans one-third of its surface, and Epimetheus and Janus periodically trade orbits.

Saturn is perhaps best known for its ring system. The seven rings, made of pieces of ice, encircle Saturn at its equator. They were first observed in 1610 by astronomer Galileo Galilei, who described them as “cup handles.” It was Dutch astronomer Christiaan Huygens who described the objects as a ring, in 1659. He believed there was only one ring, made of a solid sheet of material. In 1675, Italian-born French astronomer Giovanni Domenico Cassini announced there were two rings, and subsequent observations revealed seven. Recent missions to the planet have shown that the ring system is changing, with some areas growing dimmer, and others moving closer to the planet.








Saturn

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