What are the distinguishing characteristics of Neptune?

It’s blue.
Neptune like its twin Uranus has an atmosphere composed of hydrogen helium methane and ammonia. The methane creates the blue color. Neptune’s internal structure is also the same as that of Uranus.
The core of Neptune is probably composed of liquid rock. Then farther up the liquid rock slowly gives way to an ocean primarily containing hydrogen helium and water but also ammonia and methane. This ocean accounts for most of Neptune’s bulk. The ocean slowly thins out into .
This atmosphere contains much more detail than Uranus’. It has swirls of clouds and high-altitude cirrus clouds as well as gigantic .
Neptune also has a faint system of rings. The rings are made of pieces of material the size of a car or truck. There is about one thousandth of the in Neptune’s rings as in Uranus.
In the outermost ring of Neptune there are three anomalies called the Three Arcs of Neptune. They are areas where the rings are relatively dense. Over the millions of years the particles in the arcs should have spread out until the ring was a uniform density. However this has not happened. Scientists now believe that these arcs are shepherded by small moons.
Unique Characteristics:
Neptune is the last non-controversial planet in the solar system yet discovered (Pluto is still under debate in some circles).
Neptune’s Great Dark Spot. The next feature that is unique to Neptune is the Great Dark Spot (left). The Dark Spot is a depression in the atmosphere surrounded by high cirrus clouds. Neptune’s Great Dark Spot does not appear to be stable though. A few years after the Voyagers found it it had disappeared. Then in 1995 it reappeared in Neptune’s northern hemisphere.
When the Great Dark Spot was first discovered it was thought to be moving very slowly. However when Neptune’s rotation rate was finally determined it showed that the Great Dark Spot wasn’t moving slowly with the planet but was actually moving in a direction opposite the planet’s spin at almost supersonic speeds. These are ten times hurricane speeds on Earth.