For information on one of the planets please click on one of the links below

Saturn.

Saturn is the second of the 4 gas giants.  Like Jupiter it gives off more heat than it gets from the Sun. But unlike Jupiter, it has a magnificent set of rings, and it's so light that it would float in water - if you could find a body of water big enough!

Saturn is roughly 120,000 km across. It takes 29.46 years to go around the Sun. Like Jupiter, it spins very rapidly - the day lasts for 10 hours and 39 minutes. It has a similar structure to Jupiter. It has a solid core, which is surrounded by a shell of solid hydrogen, which is in turn surrounded by a shell of liquid hydrogen, and then the giant shell of atmosphere. Saturn has severe winds which travel at some 1,700 km/hr near the equator - 3.5 times faster than the winds on Jupiter

But Saturn has - the Great White Spot. It appears about every 30 years - fairly close to the 29.46 year of Saturn. It has previously appeared in 1876, 1903, 1933, and 1960, and it last appeared on September 24, 1990. As before, it appeared in the mid-summer of the northern hemisphere of Saturn. It very rapidly grew to an oval big enough to swallow 3 Earths, and then stayed the same size for about 3 weeks. Then the 1,700 km/hr winds began to change the Great White Spot, and it became even larger as it grew a long tail that began to stretch around the planet.

The ring system was first seen by Galileo in July 1610. His telescope was not very sharp, so he thought that Saturn was actually a central planet with two very large moons - one on each side. But when he looked again in 1617, the rings had tilted to be edge-on and almost invisible. He thought that Saturn had "swallowed its children". But telescopes improved, and around 1650, Huygens first saw the rings.

The rings are very thin, less than 1,000 metres thick. They are very delicate blocks of water ice. There are over 10,000 separate sets of rings. In the range 9 to 11 metres of size (size of a small truck), there are about 150 ice boulders per square kilometre of ring. But when you look at ice blocks the size of a car (3-5 metres across), there are about 3,000 lumps of ice per square kilometre. There are even very thin braided rings that are kept in place by tiny "shepherd" moons. These shepherd moons persistently push the braided rings back into place.

Altogether there are at least 30 moons orbiting around Saturn. Some of them have solid water ice on the surface (and maybe oceans of liquid water underneath). But the most interesting moon of all is Titan. Titan is a huge moon that is bigger than the planet Mercury. It has an atmosphere that is about 1.6 times thicker than our own atmosphere on Earth. This opaque orange smog of an atmosphere is about 50 km thick.