Saturn is the sixth planet from the Sun and the second largest planet after Jupiter. Best known for its stunning rings, Saturn is also unique in other ways. It is the least dense of all the planets – with a density of only 0.7 g/cm3, it would float in water, if that were possible. It is also the most oblate planet. The diameter at the poles is 10% smaller than the diameter at the equator. All of the gas giant planets are oblate – it’s a natural consequence of a rotating liquid. But Saturn’s rapid rotation (it only takes the giant planet about 10 1/2 hours to spin once!) flattens it enough for the effect to be visible from Earth. Saturn also has the fastest equatorial winds in the solar system: up to 500 meters per second (1,100 miles per hour) – this is 2/3 the speed of sound on Saturn!
Jupiter and Saturn are similar in many ways. Like Jupiter, Saturn’s atmosphere is about 75% hydrogen and 25% helium, with traces of water, ammonia, methane, and some silicates. Jupiter and Saturn both have long-lived storm systems. The two largest planets also have the same internal structure: gaseous atmosphere over a metallic hydrogen layer, and a solid core at the center. They also both have significant magnetic fields and aurorae at their poles.
However, Saturn’s greater distance from the Sun affects it in several ways. The most obvious is its color: although Saturn has bands and belts like Jupiter, they are not as distinct or as brightly colored. This is because in Jupiter’s atmosphere, ultraviolet radiation from the Sun breaks up molecules like methane and hydrogen sulfide. The resulting sulfur and hydrocarbons give Jupiter its vivid colors. With less solar radiation, Saturn lacks the molecules that color Jupiter’s clouds. Saturn also has more ammonia than Jupiter, again because of its lower temperature. The ammonia clouds are white. The white haze at the poles is methane, also a result of the reduced amount of solar radiation at Saturn’s orbital distance.
Of course, Saturn’s remarkable ring system is the primary attraction of this giant planet. The icy rings are by far the brightest and most visible in the solar system, and have been observed since the invention of the telescope. The Voyager missions revealed intricate structures within the rings – spokes, waves, clumps, and gaps – that are still not completely understood. Billions of ring particles are joined in their paths around Saturn by more than thirty satellites. They range in size from the huge haze-covered Titan, with its unique nitrogen atmosphere, down to tiny chunks of rock tens of kilometers in diameter, whose orbits seem to define the edges of various rings.
Author: Chris Impey
Editor/Contributor: Ingrid Daubar-Spitale
Editor/Contributor: Pamela Gay