Largest moon of Neptune, modestly larger than Pluto and Eris. In an irregular orbit, possibly a captured Kuiper Belt object. A capture method involving a binary moon of Triton has been proposed. Currently has a high inclination to Neptune, high axial tilt, and retrograde orbit, but tidal forces have given it a synchronous rotation and circular orbit, and it is nearer to its planet and much larger than other irregular satellites in the Solar System. Observed by Voyager 2. Found to have ice geysers and a thin but significant atmosphere.