This is an image of Triton.
Click on image for full size
NASA
Triton Composition
Not only ice but several different kinds of snow (crushed ice) have been found on the surface of Triton.
An idea of what the inside of Triton is made of can only be guessed because the Voyager spacecraft could not measure the inside of the moon when it flew by in 1989.
A good guess is that Triton is made of ice, except for a small core of rocky material at the center. There may be a small layer of water inside Triton too, however this depends on whether the inside of Triton is warm. A small layer of water could make an environment where life could be found. Only more exploration will help us know for sure if these things are possible.
The fact that this moon is made primarily of ice suggests a certain path for it's history.
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