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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.
Voyager 2 revealed storms raging in Neptune's atmosphere. The largest one was named the "Great Dark Spot" which is a storm that's similar to Jupiter's Great Red Spot--including its geographic location on the planet. It has winds up to 1,000 miles an hour.
Astronomers could not locate this storm with the Hubble telescope after it was re-calibrated in 1994.