Triton

"Discovered in 1846 but not named for decades later, Triton draws its name from the son of Poseidon (Neptune to the Romans), the god of the sea in Greek mythology.Consisting mainly of water ice and frozen nitrogen with a rocky core, Triton counts for 99.5% of the mass of all of Neptune's 14 moons. It is also one of the few moons in the solar system to be geologically active, meaning its surface is relatively young with sparse impact craters, and a complex geological history revealed in intricate cryovolcanic and tectonic terrains."