Saturn, the sixth planet from the Sun, has the most spectacular set of rings in the solar system. Saturn has been known since prehistoric times. Saturn is visibly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters vary by almost 10% (120,536 km vs. Saturn also exhibits long-lived ovals (red spot at center of image at right) and other features common on Jupiter. Saturn's rings remained unique in the known solar system until 1977 when very faint rings were discovered around Uranus (and shortly thereafter around Jupiter and Neptune). Saturn is the least dense of the planets; its specific gravity (0. Saturn is visibly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters vary by almost 10% (120,536 km vs.

Rings

Rings are 270,000 km in diameter, but only a few hundred meters thick. Early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn's rings every few years as Saturn moves in its orbit. Saturn's rings are extraordinarily thin: though they're 250,000 km or more in diameter they're less than one kilometer thick. Two prominent rings (A and B) and one faint ring (C) can be seen from the Earth. The origin of the rings of Saturn (and the other jovian planets) is unknown. The current set of rings maybe only a few hundred million years old.

Satellites

The rings and the larger satellites are visible with a small astronomical telescope. There are satellites within the rings which result in the gaps that are present between some rings. Though they may have had rings since their formation, the ring systems are not stable and must be regenerated by ongoing processes, perhaps the breakup of larger satellites. Saturn has at least 35 naturally occurring satellites. All five, like the newly discovered four outer moons of Saturn, are irregular satellites.

Saturn's interior is hot (12000 K at the core) and Saturn radiates more energy into space than it receives from the Sun. Saturn's rings, unlike the rings of the other planets, are very bright (albedo 0. Saturn is the most oblate (flattened) planet in our Solar System. Saturn's outermost ring, the F-ring, is a complex structure made up of several smaller rings along which "knots" are visible. Saturn also exhibits long-lived ovals (red spot at center of image at right) and other features common on Jupiter. Saturn's bright rings are made of ice chunks (and some rocks) that range in size from the size of a fingernail to the size of a car. Saturn is visible without using a telescope, but a low-power telescope is needed to see its rings. Saturn is the only planet in our Solar System that is less dense than water. Saturn's auroral displays are caused by an energetic wind from the Sun that sweeps over the planet, much like Earth's aurora, which is occasionally seen in the nighttime sky.