A billion and a half miles beyond Uranus was Neptune, and Voyager 2's last encounter with a planet. Neptune has a gaseous hydrogen and helium upper layer over a liquid interior. Like Uranus, Neptune's blue appearance is due to methane in the atmosphere.
Since Neptune receives so little sunlight, It was expected to be less active than the other giant planets. But Neptune's atmosphere proved to be surprisingly active, with winds blowing westward, opposite the direction of rotation, at more than 1,500 miles per hour -- faster winds than on any other planet.
A giant storm the size of Earth was spotted in Neptune's atmosphere. Called the Great Dark Spot, it is reminiscent of Jupiter's Great Red Spot. It has winds that blow counter-clockwise and move westward at almost 745 miles per hour. A small, irregularly shaped, eastward-moving cloud, called a "scooter", was seen darting around Neptune about every 16 hours.
Like all of the other giant planets, Neptune was found to be completely encircled by rings rather than the partial rings or ring-arcs that could be detected from Earth. Some of its rings are diffuse, dusty sheets, while others have unevenly spaced clumps of dense material. Two moons, Nereid and Triton, were known to orbit Neptune, but six more were found. The new moons are all very dark and small, ranging from 30 to 250 miles in diameter.
