Saturn, a ringed gas giant

 
Saturn, a ringed gas giant

Image Credit: NASA/JPL/Space Science Institute

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System. It is classified as a gas giant planet because the exterior is predominantly composed of gas and it lacks a definite surface, although it probably has a solid core.

Saturn has an average radius about nine times that of Earth. It has only one-eighth the average density of Earth, what makes it the only planet of the Solar System that is less dense than water; about 30% less. With its larger volume Saturn is just over 95 times as massive as Earth. Its magnetic field is slightly weaker than Earth’s and around one-twentieth the strength of Jupiter’s.

The average distance between Saturn and the Sun is over 1.4 billion kilometres (9 AU), and it takes the planet about 29½ years to finish one revolution around the Sun. But, Saturn spins faster than any other planet except Jupiter, completing a rotation roughly every 10½ hours. This rapid spinning causes Saturn to bulge at its equator and flatten at its poles — the planet is 13,000 km wider at its equator than between the poles.

Saturn has a very hot interior, reaching 11,700 °C at the core, and radiates 2.5 times more energy into space than it receives from the Sun. This interior is probably composed of a core of iron, nickel and rock with a diameter of about 25,000 km. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of hydrogen and helium that gradually transitions into gas with increasing altitude. The outermost layer which spans some 1000 km is gaseous.

Saturn’s atmosphere exhibits a banded pattern similar to Jupiter’s, but Saturn’s bands are much fainter and are much wider near the equator.

The outer atmosphere of Saturn contains 96.3% molecular hydrogen, 3.25% helium, completed with a small amount of heavier elements. The atmosphere is generally bland, although long-lived features are known, like the Great White Spot, a unique but short-lived phenomenon that occurs once every Saturnian year. Wind speeds on Saturn can reach 1,800 km/h (1,100 mph).

The composition of Saturn’s clouds varies with depth and increasing pressure. In the upper cloud layers, the clouds consist of ammonia ice. Then come clouds of water ice intermixed with a band of ammonium hydrosulfide ice. Finally, the lower layers contain a region of water droplets with ammonia in aqueous solution.

Saturn is probably known best for its ring system that consists of nine continuous main rings and three discontinuous arcs, composed mostly of water ice particles with a smaller amount of rocky debris and dust. The rings extend from 6,630 km to 120,700 km above Saturn’s equator, average approximately 20 meters in thickness.

There are two main theories regarding the origin of the rings. One theory is that the rings are remnants of a destroyed moon of Saturn. The second theory is that the rings are left over from the original nebular material from which Saturn formed. In the past, it was believed that the rings formed alongside the planet when it formed billions of years ago. Instead, the age of these rings is probably only hundreds of millions years. Some ice in the central rings comes from Enceladus’ ice volcanoes.

Saturn has at least 62 moons, 53 of which have formal names. This does not include the hundreds of “moonlets” within the rings. Some of these moons act as shepherd moons to confine the rings and prevent them from spreading out.

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