Of to 10% of its mass and extends

Of the many planets in our solar system, Neptune is not the most widely discussed. Neptune is the eighth and farthest planet from the Sun in our Solar System.  Neptune is an ice giant, which means it is smaller and has higher concentrations of volatiles than Jupiter or say Saturn. Much like Jupiter and Saturn, the atmosphere of Neptune is mostly made up of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, but it contains a higher proportion of “ices” such as water, ammonia, and methane. However, its interior, like that of Uranus, is primarily composed of ices and rock, which is why Uranus and Neptune are normally considered “ice giants” to emphasize this distinction. Traces of methane in the outermost regions in part account for the planet’s blue appearance. The mantle of the planet is equivalent to about 10 to 15 Earth masses and is rich in water. As is customary in planetary science, this mixture is referred to as icy even though it is a hot, dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water-ammonia ocean. The mantle may consist of a layer of ionic water where the water molecules break down into hydrogen and oxygen ions and deeper down superionic water in which the oxygen crystallizes. At a depth of 7,000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones. Neptune’s internal structure resembles that of Uranus. Its atmosphere forms about 5% to 10% of its mass and extends to maybe 10% to 20% of the way towards the core. Increasing concentrations of methane, ammonia, and water are found in the lower regions of the atmosphere. Neptune’s weather is characterized by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s, nearly reaching supersonic flow. More typically, by tracking the motion of persistent clouds, wind speeds have been shown to vary from 20 m/s in the easterly direction to 325 m/s westward. At the cloud tops, the prevailing winds range in speed from 400 m/s along the equator to 250 m/s at the poles. Most of the winds on Neptune move in a direction opposite the planet’s rotation. The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is thought to be a “skin effect” and not due to any deeper atmospheric processes. The relative “hot spot” is due to Neptune’s axial tilt, which has exposed the south pole to the Sun for the last quarter of Neptune’s year, or roughly 40 Earth years. As Neptune slowly moves towards the opposite side of the Sun, the south pole will be darkened and the north pole illuminated, causing the methane release to shift to the north pole. Neptune has a planetary ring system, though one much less substantial than that of Saturn. The rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue. The three main rings are the narrow Adams Ring, 63,000 km from the center of Neptune, the Le Verrier Ring, at 53,000 km, and the broader, fainter Galle Ring, at 42,000 km. A faint outward extension to the Le Verrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km. The existence of arcs was difficult to explain because the laws of motion would predict that arcs would spread out into a uniform ring over short timescales. Astronomers now estimate that the arcs are corralled into their current form by the gravitational effects of Galatea, a moon just inward from the ring. The first of these planetary rings was detected in 1968 by a team led by Edward Guinan. In the early 1980s, analysis of this data along with newer observations led to the hypothesis that this ring might be incomplete. Evidence that the rings might have gaps first arose during a stellar occultation in 1984 when the rings obscured a star on immersion but not on emersion. Images from Voyager 2 in 1989 settled the issue by showing several faint rings.