Triton

Triton is the largest moon of planet Neptune and the only large moon in the solar system with a retrograde orbit in the opposite direction from Neptune's rotation. Triton is thought to have been a dwarf planet captured by Neptune from the Kuiper belt.
Its surface is covered in nitrogen ice and water ice, with active nitrogen cryogeysers and water ice cryvolcanoes. Triton has a thin nitrogen atmosphere and a subsurface water ocean.

Type

Planetoid / Moon

Location under

Neptune