Introductory Astronomy: The Planet NEPTUNE

Basic Facts:
Average distance from Sun: 30.1 AU
Period of revolution about Sun: 164.8 years
Period of rotation: 17.3 hours
Radius: 3.9 Earth radii
Mass: 17.1 Earth masses
Average Density: 1.7 g/cm^3
Magnetic Field: 100 times Earth's, highly inclined
Surface features: great dark spot, circulation and smaller spots visible, rings, moons
Atmosphere: 84% H2, 14% He, 3% methane
Temperature: -353 degrees Fahrenheit

Like Uranus, Neptune's color is due to the presence of methane in its atmosphere. Neptune has only 1% more methane than Uranus, but this is enough to make it a much deeper blue color. Atmospheric circulation is visible on Neptune; in fact, it even has a , like the Great Red Spot on Jupiter. This Spot is due to rising currents of gas. (However, the Hubble Space Telescope didn't see the Great Dark Spot when it last looked at Neptune; it could be that the storm is over!) The cloud patterns on Neptune are driven by heat flowing from the interior and the planet's rapid rotation.

Neptune has a ring system, like all giant planets. Its narrowest rings appear to have lots of dust while the broader rings do not. The rings are made of rocky material (as opposed to ices) so they do not reflect light as well.

Neptune has at least 8 moons. Six are small, dark, rocky moons which orbit within the rings themselves. The other two, Triton and Nereid, have peculiar orbits, which suggests that the system was disturbed at one time by an interaction with another celestial object. Nereid has a highly elliptical orbit, and Triton actually orbits Neptune backwards (in the direction opposite to the rotation of Neptune). Triton is cold enough to retain an atmosphere of nitrogen and methane which is hundreds of thousands of times less dense than the Earth's. Astronomers have found faults and evidence of past volcanic activity on Triton. There is also evidence of vents of methane which spew up into Triton's atmosphere when the crust is warmed by the Sun.

To learn more about Neptune, its rings, and moons, click here.