triton

Triton is the largest of Neptune's 13 moons. 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.

Scientists think Triton is a Kuiper Belt Object captured by Neptune's gravity millions of years ago. It shares many similarities with Pluto, the best known world of the Kuiper Belt.

Like our own moon, Triton is locked in synchronous rotation with Neptune―one side faces the planet at all times. But because of its unusual orbital inclination both polar regions take turns facing the Sun.