Source: https://science.nasa.gov/neptune/moons/triton

Selected source excerpts (not the complete document).

It is unusual because it is the only large moon in our solar system that orbits in the opposite direction of its planet's rotation―a retrograde orbit.

It is so cold that most of Triton's nitrogen is condensed as frost, giving its surface an icy sheen that reflects 70 percent of the sunlight that hits it.
