Animation of the rings of Saturn, pulling back to show its system of moons. Saturn is the second-largest planet in the Solar System, with an equatorial diameter of some 120, 000 kilometres. The planet is known for its spectacular rings, which extend roughly the planet's width again either side of it. The rings are very thin, no more than a few metres in depth in places, and are made up of billions of small icy bodies. Saturn has the most extensive system of moons of any planet, with 53 named moons and many smaller ones. Its largest moon, Titan, is larger than the planet Mercury, and has a thick atmosphere with hydrocarbon lakes on its surface.