Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Named after the Roman god Saturn, its astronomical symbol represents the god’s sickle. Saturn has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610; he noted its odd appearance but was confused by it.
Saturn’s interior is probably composed of a core of iron, nickel and rock (silicon and oxygen compounds), surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium and an outer gaseous layer.
The planet exhibits a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn’s planetary magnetic field, which is slightly weaker than Earth’s and around one-twentieth the strength of Jupiter’s.
Saturn was first visited by NASA’s Pioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini (a joint NASA / ESA project) arrived on July 1, 2004 and will orbit Saturn for at least four years.
Saturn is visibly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation and fluid state. The other gas planets are also oblate, but not so much so. Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water.
Saturn is classified as a gas giant planet because the exterior is predominantly composed of gas and it lacks a definite surface, although it may have a solid core.
Basically, a quick fact about Saturn (from NASA) is the following:
- Saturn is huge. It is the second largest planet in our Solar System. Jupiter is the only planet that is bigger.
- You cannot stand on Saturn. It is not like Earth. Saturn is made mostly of gases. It has a lot of helium. This is the same kind of gas that you put in balloons.
- Its beautiful rings are not solid. They are made up of bits of ice, dust and rock.
- Some of these bits are as small as grains of sand. Some are much larger than tall buildings. Some are up to a kilometer (more than half-a-mile) across.
- The rings are huge but thin. The main rings could almost go from Earth to the moon. Yet, they are less than a kilometer thick.
- Other planets have rings. Saturn’s rings are the only ones that can be seen from Earth. All you need is a small telescope.
- Saturn could float in water because it is mostly made of gas. (Earth is made of rocks and stuff.)
- It is very windy on Saturn. Winds around the equator can be 1,800 kilometers per hour. That’s 1,118 miles per hour! On Earth, the fastest winds “only” get to about 400 kilometers per hour. That’s only about 250 miles per hour.
- Saturn goes around the Sun very slowly. A year on Saturn is more than 29 Earth years.
- Saturn spins on its axis very fast. A day on Saturn is 10 hours and 14 minutes.
- The Ringed Planet is so far away from the Sun that it receives much less sunlight than we do here on Earth. Yes, the Sun looks smaller from there.
- The day Saturday was named after Saturn.
Voyager confirmed the existence of puzzling radial inhomogeneities in the rings called “spokes” which were first reported by amateur astronomers (left). Their nature remains a mystery, but may have something to do with Saturn’s magnetic field.
Saturn’s outermost ring, the F-ring, is a complex structure made up of several smaller rings along which “knots” are visible. Scientists speculate that the knots may be clumps of ring material, or mini moons. The strange braided appearance visible in the Voyager 1 images (right) is not seen in the Voyager 2 images perhaps because Voyager 2 imaged regions where the component rings are roughly parallel. They are prominent in the Cassini images which also show some as yet unexplained wispy spiral structures.
Saturn has 53 named satellites (as of spring 2010):
- The three pairs Mimas-Tethys, Enceladus-Dione and Titan-Hyperion interact gravitationally in such a way as to maintain stable relationships between their orbits: the period of Mimas’ orbit is exactly half that of Tethys, they are thus said to be in a 1:2 resonance; Enceladus-Dione are also 1:2; Titan-Hyperion are in a 3:4 resonance.
- See Scott Sheppard’s site for the latest about recently discovered moons (there are lots).
- There are 9 more that have been discovered but as yet not named.