Neptune
Neptune is the eighth planet from the Sun. It appears in a telescope as a small greenish disk with no markings. Because of its greater distance, Earth-based study is even more difficult than for Uranus. In August 1989 Voyager 2 passed through the Neptune system.
Statistics
Distance from Sun 4,497 million km 2,795 million miles
Orbital eccentricity 0.009
Orbital inclination 1.77°
Orbital period 164.8 years
Rotation period 0.75 days
Axial tilt 29.6°
Diameter 49,528 km 30,782 miles
Surface gravity (Earth = 1) 1.14
Surface material ?
Atmosphere hydrogen, helium methane
Moons 8
Orbit
Neptune lies in a nearly circular orbit averaging 30.1 AU from the Sun. The orbit makes an angle of 1.8° to the ecliptic. Neptune orbits the Sun once in 164.8 years.
Morphology
Like Uranus, Neptune probably has a small, dense core of rock and metals. The core seems to be wrapped in a layer of water and liquid methane.
The magnetic field of Neptune is highly tilted, like the field at Uranus. It is tilted about 47° from the planet's spin axis.
Atmosphere
The atmosphere of Neptune is primarily hydrogen and helium. Small amounts of methane, and ethane have also been detected. The atmosphere of Neptune seems to be quite dynamic, like that of Jupiter's. In the southern hemisphere of the planet a large, dark, hurricane-like storm similar to the Jovian Red Spot was observed. It was named the Great Dark Spot. Several bright cirrus clouds of frozen methane are also visible. Pushed around by Neptune's strong winds, these clouds may originate from deeper in Neptune's atmosphere.
Rings
Neptune has a very faint, diffuse system of rings. The existence of partial rings had been suspected since 1984. It wasn't known until Voyager 2 visited the planet that the rings are actually complete.
Moons
Naiad, Thalassa, Despoina, Galetea, Larissa, Proteus, Triton, NereidData © Galen Raben