What is the largest moon of Saturn?

Titan, bigger than Mercury, and the only moon in the Solar System with a substantial atmosphere - nitrogen, at about one and a half times Earth's surface pressure. It is also the only place other than Earth known to have standing liquid on its surface: lakes and seas, with rivers, deltas and rain, all made of methane and ethane, because at minus 180 degrees methane does what water does here.

The Huygens probe landed there in 2005, the most distant landing ever made, and returned pictures of a shoreline covered in rounded pebbles of water ice - rounded, which means something has been tumbling them in a flow. It also recorded a soft landing into something with the consistency of wet sand.

It is a serious candidate for life, though not the familiar kind. Beneath the surface there is thought to be a water ocean, and on the surface there is a rich organic chemistry with no liquid water at all - so Titan offers two independent experiments in the same place. The Dragonfly mission, a nuclear-powered rotorcraft that will fly between sites rather than drive, is due to arrive in the 2030s.