Whatever the case, Voyager 2 will hopefully enlighten us. Neptune's big attraction, however, is the moon Triton, first seen a few weeks after the discovery of Neptune. Orbiting at a distance of 353,000 km from Neptune, very little is known about Triton. Given its orbital and axial inclination, Triton is presented with a changing cycle of mild and very extreme season. Of some certainty, however, is the presence of methane in some state on Triton.
Some doubt does exist about the actual physical state of the methane.
Frozen methane on the surface could explain the spectral features, as could an atmosphere of methane gas. However, as methane ice is quite volatile, methane ice on the surface means that there must be methane gas in the atmosphere. Methane ice is colourless, and yet Triton is definitely orange. As such, it may be that there are complex organic compounds on Triton's surface, like the organic compounds that colour Titan's atmosphere. At present, it is also thought that nitrogen may exist.