Our Solar System - Neptune
Neptune is the eighth and furthest planet from the Sun in the Solar System. It is the fourth largest planet by diameter, and the third largest by mass. Neptune is 17 times the mass of
Earth and is slightly more massive than its near twin Uranus. Neptune's atmosphere is primarily composed of hydrogen and helium along with traces of methane. The methane in the atmosphere, in part, accounts for the planet's blue appearance, but because Neptune's colour is much more vivid than that of Uranus, which has a similar amount of methane, another component is presumed to contribute to Neptune's intense colour. Neptune also has the strongest winds of any planet in the solar system, measured as high as 2,100 km/h. At the time of the 1989 Voyager 2 flyby, it had in its southern hemisphere a Great Dark Spot comparable to the Great Red Spot on Jupiter. Neptune's temperature at its cloud tops is usually close to -218 degrees C, one of the coldest in the solar system, due to its great distance from the sun. The temperature in Neptune's center is about 7,000 degrees C, which is comparable to the Sun's surface and similar to most other known planets. Discovered on September 23, 1846, Neptune was the first planet discovered by mathematical prediction rather than regular observation. It has been visited by only one spacecraft, Voyager 2, which flew by the planet on August 25, 1989.
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