An overview of Neptuen and its moons
Neptune is the outermost planet of the gas giants. It has an equatorial diameter of 49,500 kilometers (30,760 miles) and is the eighth planet from the sun. If Neptune were hollow, it could contain nearly 60 Earth's. Neptune orbits the Sun every 165 years. It has eight moons, six of which were found by Voyager 2. A day on Neptune is 16 hours and 6.7 minutes. Neptune was discovered on September 23, 1846 by Johann Gottfried Galle, of the Berlin Observatory. Neptune got its named from the Roman God of the Sea.
Much of what is know today about Neptune was discovered in 1989 by the U.S Voyager 2 spacecraft during its 1989 flyby f Neptune. Neptune as compared to Earth is 3.9 times the diameter, 30 times the distance from the sun, 17 times as massive, and 0.3 times the density.
Neptune travels around the Sun in an elliptical orbit at an average distance of 4.504 billion km (2.799 billion miles). Neptune consists largely of hydrogen and helium, and it has no apparent solid surface. The first two thirds of Neptune is composed of a mixture of molten rock, water, liquid ammonia and methane. The outer third is a mixture of heated gases comprised of hydrogen, helium, water and methane. The atmospheric composition is 85% Hydrogen, 13% Helium, and 2% methane. The planet's atmosphere, particularly the outer layers, contains substantial amounts of methane gas. Absorption of red light by the atmospheric methane is responsible for Neptune's deep blue color.
Neptune is a dynamic planet with several large, dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot, known as the Great Dark Spot, is about the size of the earth and is similar to the Great Red Spot on Jupiter.
Neptune receives less than half as much sunlight as Uranus, but heat escaping from its interior makes Neptune slightly warmer than Uranus. The heat liberated may also be responsible for Neptune's stormier atmosphere, which exhibits the fastest winds seen on any planet in the solar system. Most of the winds there blow westward, opposite to the rotation of the planet. Near the Great Dark Spot, winds blow up to 2,000 kilometers (1,200 miles) an hour. Voyager 2 found that the winds averaged about 300 meters per second (700 miles/hour) in the planet's atmosphere.
Long bright clouds, similar to cirrus clouds on Earth, were seen high in Neptune's atmosphere. At low northern latitudes, Voyager captured images of cloud streaks casting their shadows on cloud decks below.
Feathery white clouds fill the boundary between the dark and light blue regions on the Great Dark Spot. The pinwheel shape of both the dark boundary and the white cirrus suggests that the storm system rotates counterclockwise. Periodic small scale patterns in the white cloud, possibly waves, are short lived and do not persist from one Neptunian rotation to the next. (Courtesy NASA/JPL)
Until the Voyager 2...