Antique illustration showing how Saturn would float in water if there were a ocean big enough to hold it. 

Saturn, the sixth planet from the Sun, has beautiful rings omposed of ice particles. It is the second largest planet in the Solar System, yet it is the least dense (water has a density of 1.0 grams per cm cubed, while Saturn has a density of 0.69 grams per cm cubed), which means it would float in water if there were a bathtub large enough to hold it. 

Saturn is mainly composed of hydrogen and helium and does not have a solid surface. It has 25 satellites that measure at least 10km in diameter – the largest, Titan, is the only moon in the Solar System with a substantial atmosphere. 

Saturn’s interior is thought to contain fluid metallic hydrogen – a substance that cannot be studied directly because it is not possible to recreate the very high temperatures and pressures at which it is predicted to form.