Triton At 1,680 miles (2,700 km) across, Triton is the largest of the 13 moons orbiting Neptune. Unlike most large moons in our solar system, Triton orbits in the opposite direction of Neptune, called a retrograde orbit. This backward orbit leads scientists to believe that Triton formed in an area past Neptune, called the Kuiper Belt, and was pulled into its orbit around Neptune by gravity. The Voyager 2 spacecraft flew past Neptune and Triton in 1989 and found that Triton’s atmosphere is made up of mostly nitrogen…but it has not been studied in nearly 16 years!
