Saturn is named after the Roman god of wealth and agriculture; its astronomical symbol represents the god's sickle. Saturn's interior is most likely composed of a core of iron–nickel and rock. The planet's most famous feature is its prominent ring system that is composed mostly of ice particles, with a smaller amount of rocky debris and dust. At least 82 moons are known to orbit Saturn, of which 53 are officially named. Titan, Saturn's largest moon, and the second-largest in the Solar System, is larger than the planet Mercury and is the only moon in the Solar System to have a substantial atmosphere.