At 2.8 billion miles from the sun, Neptune is the most outer, and the smallest, of the gas planets in our solar system. It is the eighth planet in line, however due to its unusual elliptical orbit, it actually moves outside of Pluto for 20 years out of 248, making it temporarily the furthest planet away.
Rather than Neptune being discovered through observations, it was located through mathematical predictions on September 23rd 1846. However, until Voyager 2 travelled near to it in 1989, very little was known about it.
Since the planet was discovered, it hasn't completed a full cycle around the Sun yet, as its orbit is some 165 years. Neptune's rotation on its own axis is a lot quicker than here on Earth, it spins once in every 16.7 hours. Seasons on Neptune are extremely long at 40 years, which is the result of its orbit, rotation and tilt. Therefore, during a southern hemisphere summer, for example, the south pole is in constant sunlight for about 40 years. In a northern summer, it is a similar picture for the north pole.
Neptune's atmosphere is made up principally of hydrogen (74%) and helium (25%). The additional 1% is methane, which gives the planet its blue colour as it absorbs red light. The planet has clouds and storms which move around the planet, similar to what we have on Earth. The first two thirds of Neptune is believed to be a combination of molten rock, water, liquid ammonia and methane. The outer third is made up of the hydrogen, helium and methane mix as mentioned. However, it is also though there are some high-altitude clouds above this layer. Pictures have shown clouds which look like the cirrus clouds we experience on Earth.
Winds on Neptune are very significant and are the fastest winds every noted on a planet. They have been measured to reach over 1,500 mph. There has also been evidence of large storm systems. For example, Voyager 2 located a large dark spot in the southern hemisphere which spun in an anti-clockwise direction at speeds of up to 800 mph. Since then, there has been no observations of it, so it is thought to have disappeared, however a similar one was spotted in 1997 in the northern hemisphere.
Similarly to some of the other gas planets, Neptune has rings around it. There are four known rings, although they are thought to be quite young and short-lived and are of varying widths. The planet also has eight moons (six of which were discovered on Voyager 2's trip), the largest of which is Triton, which appears to have some significant activity on it itself.
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