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Voyager 2 was Earth's first visitor to Neptune and its Great Dark Spot.
Triton is the largest moon orbiting Neptune. According to readings from Voyager, the moon most likely did not originate from Neptune but was a lost mass that was captured by the huge planet's gravitational force. It's moving in a retrograde orbit which means it spins in the opposite direction of the planet's rotation.
Triton is about three-fourths the size of the Earth's moon. It also has about the same size, density, temperature and chemical composition as Pluto.
The most interesting discovery on Triton's surface was the presence of geyser-like volcanic vents (the black spots) that were apparently spewing nitrogen gas along with fine, dark particles. The Triton dust rose up to five miles high before descending back to the moon's surface. Triton also has a very thin atmosphere.