Saturn is the least dense planet in the Solar System. It is even less dense than water, so it could float. The planet is famous for its enormous ring system, the diameter of which is more than half the Earth-Moon distance. The rings may have been formed by a collision between two moons, or a comet and a moon. Saturn, like Jupiter, is composed mainly of hydrogen and a small amount of helium. There are also traces of ammonia, water vapour and methane.

Animation of the oppositions of Saturn throughout its orbit. Images by NASA

Both Saturn and Jupiter generate more internal heat than they receive from the Sun. This heating could be due to gravitational compression, or it may be caused by the friction of helium raining down deep inside the planets. Saturn has been visited by the Pioneer space probe, Voyager (probes one and two, not the Federation Starship). It has also been visited by the Cassini probe, which is still in orbit around Saturn.

Titan as seen from the Cassini probe. Note the haze caused by the thick atmosphere.

Titan, one of Saturn’s many moons, has an unusually thick atmosphere full of organic compounds, such as methane. Cassini dispatched the Huygens probe which landed on the moon’s surface, revealing formations very similar to those found on Earth. It found rivers and lakes of liquid hydrocarbons and sent back images of a boulder covered surface.

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