Ten times as far from the Sun as the Earth, orbits the ringed planet Saturn.

This is the realm of the Gas Giants, the cold twilight of the outer solar system.

Second only to Jupiter, Saturn is a huge planet, 95 times the mass of the Earth.

Below the clouds, Saturn can’t be said to have a solid surface in the sense that we understand such things.

Preserving much of the original material from which they formed four billion years ago, the atmospheres of the Gas Giants become thicker and thicker, till they’re denser than rocks on the Earth, yet still technically a gas.

We may send robot probes parachuting down into them - which we have already done once on Jupiter.

We may even mine them in meteoric suborbital flights which scoop the gas into fuel tanks before hurtling back out into space again, or even travel there ourselves using the very oldest form of air travel, floating high in their upper reaches in hot hydrogen balloons.

What a safari that would be!

But it is the moons and, especially, the magical rings of Saturn which occupy our interest, both scientifically and aesthetically.

No-one who has seen Saturn through a telescope will ever forget their first glimpse of it, hanging in space like a child’s toy.

Its rings seem too beautiful to be real, impossibly existing as they encircle but never touch the planet.

Knowing about them doesn’t take away their wonder. They’re made of lumps of rock and ice, all orbiting independently. There are thousands of rings, some narrow, some broad, separated by gaps in which tiny satellites orbit.

These moons shepherd the rings feed them material in the form of micro-meteors blasted off their surfaces.

Saturn has over 60 recognised satellites, from lumps of ice a few km across up to worlds like Enceladus, where geysers erupt at hundreds of km per hour, throwing material deep into space, and the giant moon Titan, larger than the Earth’s own Moon, on which a whole liquid flow cycle exists, with lakes and rivers, clouds and rain, just like that of the Earth.

The only difference is that on Earth the liquid is water; on cold Titan it is methane - which we know better as the major component of the natural gas we use for cooking.

But the rest is the same - the same rounded, eroded, hills, valleys cut by rivers and streams, rainclouds, even the stones we know as "river rocks", worn smooth by long exposure in stream beds.

Ironically, the rocks of Titan, the hard material which makes up its hills and sea-beds, and over which its rivers flow, is water ice. At a temperature of minus 170 Celsius, it shares many of the same properties as the silicate rock of the Earth’s crust.

One day we will go to Saturn and, if the prospect of riding in a balloon among its clouds doesn’t excite us, we may turn instead to sailing ships, exploring like the navigators of old Earth the coastlines and islands of Titan.

The NASA Cassini probe continues to orbit Saturn, gathering data and images which it sends back to Earth.

Imagine being there and being able to look out the window and see the ever-changing dance of its moons, and the shadow-play and majesty of its rings, set against the giant cloud-wrapped planet below.

The main source of these photos was http://saturn.jpl.nasa.gov/photos. If you have an hour to spare, it’s well worth a visit!

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Photos, filenames and captions:

Saturn moon helene.jpg - Helene: Iceberg in orbit.

Saturn moon quartet.jpg  - Four of Saturn’s sixty-plus moons, Epimetheus, Janus, Prometheus and Atlas, strung out along the planet’s ring system.

Saturn Daphnis and rings.jpg - Tiny moon Daphnis sweeps out a gap in the rings in which it is embedded, leaving tidal eddies behind in the ring material.

Saturn Enceladus geysers 2.jpg - The geysers of Enceladus, pressurised water erupting through cracks in its icy surface.

Saturn Rhea above rings and shadow.jpg - Large moon Rhea in the foreground, set against the rings seen edge-on and their shadow below on the curved body of Saturn.

Saturn Iapetus.jpg - Large moon Iapetus is almost jet black on one side and snow white on the other. As if this is not strange enough, a circular ridge or mountain chain over 10 km high runs right around its equator.

Saturn titan huygens shoreline.jpg - Extensive river valley network on Titan. In the foreground is the shoreline of the methane sea into which it flows.

Saturn whole planet and rings.jpg - Saturn, lord of the rings.

Saturn Titan River rox 3.jpg - The Huygens descent probe landed in a dry river valley on Titan, surrounded by eerily familiar rocks, eroded smooth by flowing methane.

Saturn moonshadow on rings.jpg - Small moon Epimetheus throws a long shadow across the ring system.

Saturn Prometheus and Ring Tides.jpg - Prometheus clears out a gap in the rings, drawing tidal streamers of ring matter after it