Triton is Neptune's seventh closest known moon. Triton's orbit is about 220,000 miles from Neptune and has a diameter of 1677 miles. The name Triton comes from a god of the sea, the son of Poseidon. Triton was discovered by Lassell in 1846 only a few weeks after the discovery of Neptune. The only spacecraft to visit Triton was Voyager 2 on August 25 1989.