A Dark Spot and Twisted Rings

Neptune appears bluer than Uranus because there is more methane in Neptune's atmosphere. Methane absorbs red light better than blue, and thus the more methane, the bluer the atmosphere. Actually, methane is only 5 percent of the atmosphere, with molecular hydrogen and helium making up the rest. Neptune's atmosphere is also far more active and shows features.

Jupiter can have its Great Red Spot, Neptune has its Great Dark Spot. About the size of Earth, this spot appears to be rising currents of gas. Smaller spots, named Scooter and D2 are found in the southern latitudes. Wispy clouds of frozen methane ice crystals in the upper atmosphere are also visible.

Since the atmosphere changes over time, something has to be driving it. Astronomers believe that the atmosphere is being driven by heat flowing from the interior. This rising heat causes convection in the atmosphere which, along with the rapid rotation of Neptune, causes high speed winds to develope.

. We know there is heat from internal sources because Neptune's temperature is about 60K, if it were heated by the Sun alone the temperature would be closer to 44K. In fact, Neptune gives off three times more energy than it receives from the Sun! The only logical explanation for this internal heat is leftover heat from Neptune's formation.

With a density of 1.2 g/cm3, Neptune is more dense than Uranus and probably has a slightly larger rocky core. The current model for Neptune is a a rocky core surrounded by a slushy mix of molecular hydrogen, ammonia and methane with thick layers of water clouds.

Rings have turned out to be a common thing in the outer solar system, and Neptune is no exception, though they are strange rings indeed. The best description of Neptune's rings are that they are lumpy and twisted! The reason for this strange appearance is directly connected with the moons of Neptune.

Neptune is surrounded by four dark rings. Three are narrow like the rings around Uranus, but one is fairly broad, but more diffuse. The dark coloring is no doubt due to chemical reactions of highly charged particles striking the material in the rings.

Small moons "shepherd" the narrow rings and keep them from expanding and being more diffuse. Because these rings are brightest when backlit, they must have a great deal of small particles and dust in them.

The outermost ring is the one that is quite "lumpy" and "twisted." Astronomers were at a loss to explain this until in 1991 a planetary astronomer constructed a model to explain interaction between the ring and Neptune's moon Galatea. According to the model, there is gravitational interaction between Galatea and the outer ring. This model is now widely accepted.