Neptune has 13 moons, Triton, Nereid, Naiad, Thalassa, Despina, Larissa, Proteus, and Galatea, plus five smaller, unnamed moons. Triton and Proteus orbit close to Neptune; Nereid is in a distant orbit. Triton is the only moon in our Solar System with a retrograde orbit (orbiting in the opposite direction than its primary, Neptune, is rotating). The moon Triton is the coldest measured object in our Solar System, and Nereid is the Solar System object with the most eccentric orbit. The moons of Neptune in order of distance from Neptune.
The first four moons of Neptune, Naiad, Thalassa, Despina, and Galatea, are so close to Neptune that they orbit within its ring system. Little is known about them. The next one out, Larissa, was actually discovered in 1981, when it blocked a star. This was attributed to the ring arcs, but later was found to be the moon, being re-discovered by Voyager 2 in 1989. Proteus is the second-largest moon in orbit around Neptune. It is so close to the planet that Earth-bound telescopes cannot see it. Triton is next (right), and is one of the strangest moons in the solar system. First, it is one of only three moons in the solar system that has an atmosphere (Jupiter's Io and Saturn's Titan are the other two). It is thicker than Io's, yet much thinner than Titan's. Its pressure is 1/100,000 of Earth's. Second, Triton has a retrograde orbit, which means that it orbits the opposite way the planet spins. This is a very strong indication that Triton was captured. This in itself is not strange; both of Mars' moons were captured. What is strange is that Triton is two-thirds the size of our moon. When two bodies have a close encounter, one does not automatically capture the other, especially if it is so big. One theory is that Triton must have actually hit Neptune, bounced off the atmosphere, and gone into orbit because it lost all of its momentum. Another way this could have happened is that Triton collided with one of Neptune's...
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